Physics Archives - Noon Academy

An electron microscope uses electrons accelerated by a voltage of $50 \mathrm{kV}$ . Determine the de B roglie wavelength associated with the electrons. If other factors (such as numerical aperture, etc.) are taken to be roughly the same, how does the resolving power of an electron microscope compare with that of an optical microscope which uses yellow light?

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

Electrons are accelerated by a voltage of $50 \mathrm{kV}$ Charge on an electron, $e=1.6 \times 10^{-19} \mathrm{C}$ Mass of the electron, $m_{e}=9.11 \times 10^{-31} \mathrm{~kg}$ Wavelength of the...

(a) Obtain the de Broglie wavelength of a neutron of kinetic energy $150 \mathrm{eV}$ . As you have seen in question 11.31, an electron beam of this energy is suitable for crystal diffraction experiments. Would a neutron beam of the same energy be equally suitable? Explain. $\left(m_{n}=1.675 \times 10^{-27} \mathrm{~kg}\right)$ .
(b) Obtain the de B roglie wavelength associated with thermal neutrons at room temperature (27 °C). Hence explain why a fast neutron beam needs to be thermalised with the environment before it can be used for neutron diffraction experiments.

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

(a) Kinetic energy of the neutron is given as $=150 \mathrm{eV}$ $=150 \times 1.6 \times 10^{-19}$ $=2.4 \times 10^{-17} \mathrm{~J}$ Mass of the neutron, $m_{n}=1.675 \times 10^{-27} \mathrm{~kg}$...

Crystal diffraction experiments can be performed using $X$ -rays, or electrons accelerated through appropriate voltage. Which probe has greater energy? (For quantitative comparison, take the wavelength of the probe equal to $1 \AA$ , which is of the order of interatomic spacing in the lattice) $\left(m_{e}=9.11 \times 10^{-31} \mathrm{~kg}\right)$

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

For Electrons, we have the relation for kinetic energy as,$\mathrm{K} . \mathrm{E}=(1 / 2) \mathrm{m}_{\mathrm{e}} \mathrm{V}^{2}$ $=\left(\mathrm{m}_{\mathrm{e}} \mathrm{V}\right)^{2} / 2...

Light of intensity $10^{-5} \mathrm{~W} \mathrm{~m}^{-2}$ falls on a sodium photo-cell of surface area $2 \mathrm{~cm}^{2}$ . Assuming that the top 5 layers of sodium absorb the incident energy, estimate the time required for
photoelectric emission in the wave-picture of radiation. The work function for the metal is given to be about $2 \mathrm{eV} .$ What is the implication of your answer?

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

Intensity of the light is given as $=10^{-5} \mathrm{~W} \mathrm{~m}^{-2}$ Surface area of the sodium photocell is given as $A=2 \mathrm{~cm}^{2}$ Incident power of the light is given by the...

The work function for the following metals is given: Na: $2.75$ eV; K: $2.30$ eV; Mo: $4.17$ eV; Ni: $5.15 \mathrm{eV} .$ Which of these metals will not give photoelectric emission for radiation of wavelength 3300 \AA from a He-Cd laser placed 1 m away from the photocell? What happens if the laser is brought nearer and placed $50 \mathrm{~cm}$ away?

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

Wavelength is given as $\lambda=3300 \AA$ Speed of light $=3 \times 10^{8} \mathrm{~m} / \mathrm{s}$ Planck's constant $=6.63 \times 10^{-34} \mathrm{~J} \mathrm{~s}$ Energy of the photon of the...

A mercury lamp is a convenient source for studying the frequency dependence of photoelectric emission since it gives a number of spectral lines ranging from the UV to the red end of the visible spectrum. In our experiment with rubidium photo-cell, the following lines from a mercury source were used:
$\lambda_{1}=3650 \AA$ $\lambda_{2}=4047 \AA$ $\lambda_{3}=4358 \AA$ $\lambda_{4}=5461 \AA$ , $\lambda_{5}=6907 \AA$ . The stopping voltages, respectively, were measured to be: $\mathbf{V}_{01}=1.28 \mathrm{~V}, \mathrm{~V}_{02}=0.95 \mathrm{~V}, \mathrm{~V}_{03}=0.74 \mathrm{~V}$ , $\mathrm{V}_{04}=0.16 \mathrm{~V}, \mathrm{~V}_{05}=0 \mathrm{~V}$ .Determine the value of Planck’s constant $\mathrm{h}$ , the threshold frequency and work function for the material.

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

The following relation can be derived from photoelectric effect,$eV_{o}=hv-\phi_{o}$ Work function of the metal, $\Phi_{0}=\mathrm{hv}-\mathrm{eV}_{0}$ $\Phi_{0}=(h c / \lambda)-e V_{0}$...

Monochromatic radiation of wavelength $640.2 \mathrm{~nm}\left(1 \mathrm{~nm}=10^{-9} \mathrm{~m}\right)$ from a neon lamp irradiates photosensitive material made of caesium on tungsten. The stopping voltage is measured to be $0.54 \mathrm{~V} .$ The source is replaced by an iron source and its $427.2 \mathrm{~nm}$ line irradiates the same photocell. Predict the new stopping voltage.

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

Wavelength of the monochromatic radiation is given as $\lambda=640.2 \mathrm{~nm}=640.2 \times 10^{-9} \mathrm{~m}$ Stopping potential of the neon lamp is also given as $V_{0}=0.54 \mathrm{~V}$...

Ultraviolet light of wavelength $2271 \AA$ from a $100 \mathrm{~W}$ mercury source irradiates a photo-cell made of molybdenum metal. If the stopping potential is $-1.3 \mathrm{~V}$ , estimate the work function of the metal. How would the photo-cell respond to high intensity $\left(\sim 10^{5} \mathrm{~W} \mathrm{~m}^{-2}\right)$ red light of wavelength $6328 \AA$ produced by a He-Ne laser?

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

Wavelength of ultraviolet light is given as $\lambda=2271 \AA{A}=2271 \times 10^{-10} \mathrm{~m}$ Stopping potential of the metal is given as $\mathrm{V}_{0}=1.3 \mathrm{~V}$ Planck's constant,...

Estimating the following two numbers should be interesting. The first number will tell you why radio engineers do not need to worry much about photons! The second number tells you why our eye can never ‘count photons’, even in barely detectable light. (a) The number of photons emitted per second by a Medium wave transmitter of $10 \mathrm{~kW}$ power, emitting radio waves of wavelength $\mathbf{5 0 0} \mathbf{~ m}$ .
(b) The number of photons entering the pupil of our eye per second corresponding to the minimum intensity of white light that we humans can perceive $\left(\sim 10^{-10} \mathrm{~W} \mathrm{~m}^{-2}\right) .$ Take the area of the pupil to be about $0.4 \mathrm{~cm}^{2}$ , and the average frequency of white light to be about $6 \times 10^{14} \mathrm{~Hz}$

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

(a) Power of the medium wave transmitter is given as $\mathrm{P}=10 \mathrm{~kW}=10^{4} \mathrm{~W}$ Energy emitted by the transmitter per secon is $E=10^{4}$ Wavelength of the radio waves is given...

In an accelerator experiment on high-energy collisions of electrons with positrons, a certain event is interpreted as the annihilation of an electron-positron pair of total energy $10.2$ BeV into two y-rays of equal energy. What is the wavelength associated with each y-ray? $\left(1 \mathrm{BeV}=10^{9} \mathrm{eV}\right)$

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

Total energy of the electron-positron pair is given as $\mathrm{E}=10.2 \mathrm{BeV}=10.2 \times 10^{9} \mathrm{eV}=10.2 \times 10^{9} \times 1.6 \times 10^{-19} \mathrm{~J}$ Hence the energy of...

(a) An $X$ -ray tube produces a continuous spectrum of radiation with its short wavelength end at $0.45 \AA$ . What is the maximum energy of a photon in the radiation?
(b) From your answer to (a), guess what order of accelerating voltage (for electrons) is required in such a tube?

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

(a) Wavelength produced by the $X$-ray tube is given to us as $\lambda=0.45 \AA=0.45 \times 10^{-10} \mathrm{~m}$ Speed of light, $c=3 \times 10^{8} \mathrm{~m} / \mathrm{s}$ Planck's constant,...

An electron gun with its collector at a potential of $100 \mathrm{~V}$ fires out electrons in a spherical bulb containing hydrogen gas at low pressure $\left(\sim 10^{-2} \mathrm{~mm}\right.$ of $\mathrm{Hg}$ ). A magnetic field of $2.83 \times 10^{-4} \mathrm{~T}$ curves the path of the electrons in a circular orbit of radius $12.0 \mathrm{~cm}$ . (The path can be viewed because the gas ions in the path focus the beam by attracting electrons, and emitting light by electron capture; this method is known as the ‘fine beam tube’ method.) Determine e/m from the data.

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

Potential of the collector is given as $V=100 \mathrm{~V}$ Magnetic field experienced by the electron is given as $\mathrm{B}=2.83 \times 10^{-4} \mathrm{~T}$ Radius of the circular orbit is given...

(a) A monoenergetic electron beam with an electron speed of $5.20 \times 10^{6} \mathrm{~m} \mathrm{~s}^{-1}$ is subject to a magnetic field of $1.30 \times 10^{-4} \mathrm{~T}$ normal to the beam velocity. What is the radius of the circle traced by the beam, given e/m for electron equals $1.76 \times 10^{11} \mathrm{C} \mathrm{kg}^{-1}$ .

(b) Is the formula you employ in (a) valid for calculating the radius of the path of a $20 \mathrm{MeV}$ electron beam? If not, in what way is it modified?

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

Magnetic field experienced by the electron, $B=1.30 \times 10^{-4} \mathrm{~T}$ Specific charge, e/m is given by $=1.76 \times 10^{11} \mathrm{Ckg}^{-1}$ Here, $e=$ charge on the electron $=1.6...

(a) Estimate the speed with which electrons emitted from a heated emitter of an evacuated tube impinge on the collector maintained at a potential difference of $500 \mathrm{~V}$ with respect to the emitter. Ignore the small initial speeds of the electrons. The specific charge of the electron, i.e., its e/m is given to be $1.76 \times 10^{11} \mathrm{C} \mathrm{kg}^{-1}$ .
(b) Use the same formula you employ in (a) to obtain electron speed for a collector potential of $10 \mathrm{MV}$ . Do you see what is wrong? In what way is the formula to be modified?

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

(a) Potential difference of the evacuated tube is given as $500 \mathrm{~V}$ Specific charge of the electron is given as $\mathrm{e} / \mathrm{m}=1.76 \times 10^{11} \mathrm{C} \mathrm{kg}^{-1}$...

What is the de Broglie wavelength of a nitrogen molecule in air at $300 \mathrm{~K} ?$ Assume that the molecule is moving with the root-mean-square speed of molecules at this temperature. (Atomic mass of nitrogen $=14.0076 \mathrm{u}$ )

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

Temperature of the nitrogen molecule is given as $\mathbf{T}=\mathbf{3 0 0} \mathbf{K}$ Atomic mass of nitrogen is $14.0076 \mathbf{u}$ Hence, mass of the nitrogen molecule will be,$\mathrm{m}=2...

Show that the wavelength of electromagnetic radiation is equal to the de Broglie wavelength of its quantum (photon).

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

The momentum of a photon having energy (hv) is given by the elation: $p=\frac{h v}{c}=\frac{h}{\lambda}$ $\lambda=\frac{h}{p} \ldots \ldots \ldots$ (i) Where, $\lambda=$ wavelength of the...

(a) For what kinetic energy of a neutron will the associated de Broglie wavelength be 1.40 x 10-10 m?
(b) Also find the de Broglie wavelength of a neutron, in thermal equilibrium with matter, having an average kinetic energy of $(3 / 2) \mathrm{kT}$ at $300 \mathrm{~K}$ .

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

(a) de Broglie wavelength of the neutron is given as $\lambda=1.40 \times 10^{-10} \mathrm{~m}$ Mass of a neutron, $m_{n}=1.66 \times 10^{-27} \mathrm{Kg}$ Planck's constant, $h=6.63 \times 10^{-34}...

An electron and a photon each have a wavelength of $1.00$ nm. Find the kinetic energy of the electron.

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

Wavelength of an electron is represented by $\lambda_{e}$ and that of a photon by $\lambda_{p}$, So, $\lambda_{e}=\lambda_{p}=\lambda=1 \mathrm{~nm}=1 \times 10^{-9} \mathrm{~m}$ Planck's constant,...

An electron and a photon each have a wavelength of $1.00$ nm. Find: (a) Their momenta, (b) The energy of the photon

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

Wavelength of an electron is represented by $\lambda_{e}$ and that of a photon by $\lambda_{p}$, So, $\lambda_{e}=\lambda_{p}=\lambda=1 \mathrm{~nm}=1 \times 10^{-9} \mathrm{~m}$ Planck's constant,...

What is the de Broglie wavelength of a dust particle of mass $1.0 \times 10^{-9} \mathrm{~kg}$ drifting with a speed of $2.2 \mathrm{~m} / \mathbf{s} ?$

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

Mass of the dust particle is given as $\mathbf{m}=\mathbf{1} \mathbf{x} \mathbf{1 0}^{-9} \mathbf{K g}$ speed of the dust particle, $\mathbf{v}=\mathbf{2 . 2} \mathbf{~ m} / \mathbf{s}$ de Broglie...

What is the de Broglie wavelength of: (a) a bullet of mass $0.040 \mathrm{~kg}$ travelling at the speed of $1.0 \mathrm{~km} / \mathrm{s}$ , (b) a ball of mass $0.060 \mathrm{~kg}$ moving at a speed of $1.0 \mathrm{~m} / \mathrm{s}$

Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

(a) Mass of the bullet is given as$\mathbf{m}=\mathbf{0 . 0 4 0} \mathrm{Kg}$ Speed of the bullet is given as $v=1.0 \mathrm{~km} / \mathrm{s}=\mathbf{1 0 0 0} \mathbf{~ m} / \mathbf{s}$ Planck's...

c) Explain how sun is considered to be the ultimate source of fossil fuels.

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

d) Which fossil fuels were formed by the buried remains of small plants and animals? e) Which fossil fuel was formed by the buried remains of large land plants? Answer – c) The sun is regarded...

a) What are fossil fuels? Give three examples of fossil fuels.

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

b) Describe how fossil fuels were formed. Answer – a) Fossil fuels are natural fuels that are created deep beneath the earth's surface from prehistoric species' remains. Fossil fuels include coal,...

Why is the leakage of LPG detected easily although it is odourless? State the steps to be taken in case its leakage is detected in the kitchen.

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: LPG is an odourless material that can nonetheless be detected by its odour due to the addition of mercaptan to the LPG. The actions to take in the event of an LPG leak in the kitchen are as...

Why is LPG considered a better fuel than coal?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: LPG is a better fuel than coal because when coal is burned, dangerous gases are released, however when LPG is burned, no harmful gases are generated..

Why is LPG considered a good fuel?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: Because of its calorific value and lack of hazardous gas production, LPG is considered a good fuel. LPG also has a high calorific value.

If you could use any source of energy for heating your food, which one would you use and why?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: LPG is utilised as a source of energy for heating food since it has a high calorific value and produces smokeless flames.

What are the various steps which can be taken to control pollution caused by burning fossil fuels?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: Increasing the efficiency of the combustion process and developing strategies to decrease the discharge of toxic gases and ashes into nature are two steps that can be taken to control...

What are the various steps which can be taken to control pollution caused by burning fossil fuels?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: Increasing the efficiency of the combustion process and, developing strategies to decrease the discharge of toxic gases and ashes into nature are two steps that can be taken to control...

Write a short note on the pollution caused by burning fossil fuels.

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: When fossil fuels are burned, acidic gases such as sulphur dioxide and nitrogen dioxide are released. Acid rain is caused by these chemicals, which harm trees, buildings, and plants while...

What are the disadvantages of burning fossil fuels?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: The following are some of the disadvantages of burning fossil fuels: a) Acidic gases are produced when fossil fuels are burned. b) The amount of smoke produced is higher, as is the amount of...

Explain the principle of working of a thermal power plant. Draw a labelled diagram to illustrate your answer.

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: Heat is generated in thermal power plants by burning coal, which is then used to boil water and create steam. When high-temperature, high-pressure steam is introduced to turbines, it causes...

What is meant by conventional sources of energy? Write the names of two conventional sources of energy.

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: Traditional sources of energy are the traditional sources of energy that a great number of people are familiar with. Wood and coal are examples of traditional energy sources.

Explain why natural gas is considered to be a good fuel.

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: Natural gas is regarded as an excellent fuel since it has a high calorific value and burns with a smokeless flame, producing no hazardous fumes.

Complete the following sentence:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Domestic gas cylinders like Indane contain mainly …… Answer: Butane

State one important use of CNG these days.

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: CNG these days is being used as a fuel in transport vehicles which results in lesser air pollution.

State two important uses of natural gas.

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: The two most important uses of natural gas are as follows: It is utilised as a fuel in thermal power plants and transportation vehicles.

Name the component which is found in natural gas as well as in biogas.

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: Butane is the component which is found in natural gas as well as in biogas.

What is the main constituent of:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) petroleum gas? b) natural gas? Answer: a) The main constituent of petroleum gas is butane b) The main constituent of natural gas is methane

Write the full form of: a) LPG b) CNG

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: a) Full form of LPG is Liquefied Petroleum Gas b) Full form of CNG is Compressed Natural Gas

Which gaseous fuel is being used increasingly in transport vehicles like cars and buses these days?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: Compressed Natural Gas is used in transport vehicles such as cars and buses.

What is the composition of liquefied petroleum gas?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: Liquefied petroleum gas is composed of butane with smaller amounts of propane and ethane.

Name any four fractions obtained from petroleum which are used as fuels.

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: Petroleum gas, diesel, kerosene, and petrol are the fractions derived from petroleum that are used as fuels.

What are the various fuels which are used to generate electricity in a thermal power plant?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: Coal, gas, and oil are the different fuels utilised in the generation of electricity in a thermal power station.

Name any one hydrocarbon fraction obtained during the fractional distillation of petroleum which is used as a domestic fuel.

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: Kerosene is a hydrocarbon fraction derived by fractional distillation of petroleum and used as a household fuel.

Give one example of a good domestic fuel.

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: Liquified Petroleum Gas is an example of a good domestic fuel.

Name the product of petroleum that is used to drive heavy vehicles.

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: The product of petroleum that is used to drive heavy vehicles is Diesel.

Which of the following is not a fossil fuel?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) coal b) petroleum gas c) biogas d) natural gas Answer: c) biogas Biogas is a renewable source while rest are non-renewable

One of the following is not a characteristics of a good fuel. This is:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) high calorific value b) no emission of smoke c) smooth burning d) high ignition temperature Answer: d) high ignition temperature High ignition temperature leads to system instability and...

There are four fuels which all contain only carbon and hydrogen. The fuel having highest calorific value will be one which has:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) more of carbon but less of hydrogen b) less of carbon but more of hydrogen c) equal proportions of carbon and hydrogen d) less of carbon as well as less of hydrogen Answer: b) less of...

The fuel having the lowest calorific value is:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) coal b) wood c) charcoal d) kerosene Answer: b) wood

Which of the following fuels has the highest calorific value?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) natural gas b) methane gas c) hydrogen gas d) biogas Answer: c) hydrogen gas

A newly planted sapling usually grows and mature into a tree in more than:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) 50 years b) 25 years c) 45 years d) 15 years Answer: d) 15 years

The fuel having a calorific value of 55kJ/g is likely to be:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) biogas b) methane gas c) hydrogen gas d) natural gas Answer: b) methane gas

A good fuel is one which possesses:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) high calorific value and low ignition temperature b) high calorific value and high ignition temperature c) high calorific value and moderate ignition temperature d) low calorific value and...

Which of the following is not a renewable source of energy?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) wind b) flowing water c) fossil fuels d) fuel wood Answer: c) fossil fuels Fossil fuels once exhausted can not be replenished.

A non-renewable source of energy is:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) wood b) alcohol c) hydrogen gas d) natural gas Answer: d) Natural gas Natural Gas once exhausted can not be replenished.

An example of a renewable source of energy is:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) petrol b) natural gas c) biogas d) kerosene Answer: c) biogas Only biogas is replenishable.

The calorific value and ignition temperature of fuel A are 55kJ/g and 80 degree Celsius respectively. These values for fuel B are 80kJ/g and 10 degree Celsius respectively. On burning, the fuel A produces CO₂ and H₂O while the fuel B produces CO₂, CO, and SO₂. Give three points of relative advantages and disadvantages of these two fuels.

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: Fuel-A i) It has a low calorific value of 55kJ/g, which is a drawback. ii) The ignition temperature is 80°C, which is moderate and advantageous. iii) No hazardous gases are created, which is...

a) What is a fuel? Give five examples of fuels.

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

b) What are the characteristics of an ideal fuel or good fuel? Answer: a) A fuel is a material that is burned to generate heat energy. The five types of fuels are wood, LPG, coal, kerosene, and...

Coal is said to be formed from the wood of trees. Why then is coal considered to be a non-renewable source of energy whereas wood is a renewable source of energy?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: Because coal takes longer to accumulate than growing trees, it is regarded a non-renewable source of energy. Whereas wood is considered a renewable source of energy. As a result, utilising...

a) Classify the following into renewable and non-renewable sources of energy:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Coal, wind, tides, petroleum, wood , natural gas b) What is the basis of above classification? Answer: Wind, tides, and wood are examples of renewable energy sources. Coal, petroleum, and natural...

Name two sources of energy which you consider to be non-renewable. Give reason for your choice.

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: Petroleum and coal are the only non-renewable sources of energy. This is due to the fact that they cannot be reclaimed once they have been fully utilised.

Name two sources of energy that you think are renewable. Give reason for your choice.

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: Air and water are renewable energy sources since they are abundant in nature and may be used repeatedly.

Why are fossil fuels classified as non-renewable source of energy?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: Fossil fuels are classified as non-renewable source of energy since once these are used completely these cannot be replenished.

What is the difference between a renewable and a non-renewable source of energy? Explain with examples.

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: The difference between a renewable and a non-renewable energy source is that a renewable energy source is abundant in nature, but a non-renewable energy source is finite. Overuse of...

What is meant by a renewable source of energy? Give two examples of renewable sources of energy.

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: A renewable energy source is described as a source of energy that is abundant in nature and may be used for an indefinite amount of time; it never runs out. Solar and wind energy are two...

What is meant by a non-renewable source of energy? Give two examples of non-renewable sources of energy.

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: A non-renewable energy source is described as one that will deplete rapidly if used for an extended length of time. These energy sources are only found in small amounts in nature. Coal and...

State any four characteristics of a good source of energy.

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: The following four properties will characterise a good source of energy: a) It's simple to store and move. b) The energy is simple to handle and secure. d) There is a lot of energy...

What is a source of energy? What are the two main categories of the sources of energy?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: A source of energy is one from which a sufficient amount of energy can be obtained over an extended period of time. The two primary categories of energy sources are as follows: a) Renewable...

Fill in the blanks with a suitable word:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

The amount of heat produced by burning a unit mass of a fuel completely is known as its ………. value. Answer: Calorific value.

“The ignition temperature of a fuel is 80 degree Celsius”. What does this mean?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: When a fuel's ignition temperature is 80 degrees Celsius, it signifies that the fuel's lowest temperature for catching fire and burning is 80 degrees Celsius.

Define ignition temperature of a fuel.

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: A fuel's ignition temperature is defined as The minimal temperature at which it must be heated in order to catch fire and begin burning.

Define ignition temperature of a fuel.

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: A fuel's ignition temperature is defined as the minimal temperature at which it must be heated in order to catch fire and begin burning.

Which of the following produces more heat per unit mass on burning?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Coal or LPG Answer: Because LPG has a larger calorific value than coal, it will create more heat per unit mass when burned.

“The calorific value of cooking gas is 50kJ/g”. What does it mean?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: Cooking gas has a calorific value of 50kJ/g, which indicates that if 1 gramme of LPG is totally burned,...

Define calorific value of a fuel.

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: The quantity of heat produced by totally burning 1 gramme of fuel is referred to as the calorific value of the fuel.

Name a non-renewable source of energy other than fossil fuels.

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

Answer: Other than fossil fuels, nuclear fuels such as uranium are a non-renewable source of energy.

The main constituent of petroleum gas is:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) methane b) ethane c) butane d) propane Answer: The correct answer is c) butane

The natural gas consists of mainly of:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) methane b) ethane c) propane d) butane Answer: The correct answer is a) methane

Which of the following is not produced by the burning of fossil fuels?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) nitrogen oxides b) sulphur oxides c) sodium oxides d) carbon oxides Answer: The correct answer is c) sodium oxides

The product of petroleum used to drive heavy vehicles like trucks is:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) petrol b) kerosene c) petrol d) CNG Answer: The correct answer is c) petrol

The aviation fuel which is used in the engines of jet aeroplanes is:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) diesel b) kerosene c) petrol d) CNG Answer: The correct answer is b) kerosene

The ultimate source of energy stored in fossil fuels is:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) moon b) earth c) sun d) sea Answer: The correct answer is c) sun

Which of the following is not a fossil source of energy?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) kerosene oil b) cow-dung cakes c) CNG d) coal Answer: The correct answer is b) cow-dung cake

The fuel which is not used at thermal plants is:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) coal b) uranium c) natural gas d) fuel oil Answer: The correct answer is b) uranium

LPG consists mainly of:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) butane b) ethane c) butanone d) methane Answer: The correct answer is a) butane

Coke is more valuable when used:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) as a fuel for industrial boilers b) as an oxidizing agent c) as a reducing agent d) as a fuel in domestic ovens Answer: The correct answer is c) as a reducing agent

Coal cannot be converted into one of the following forms of energy. This is:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) coal gas b) electricity c) oil d) charcoal Answer: The correct answer is d) charcoal

One of the following does not contribute to acid rain. That is:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) nitrogen monoxide b) sulphur dioxide c) carbon monoxide d) carbon dioxide Answer: The correct answer is c) carbon monoxide

A solar water heater cannot be used to get hot water on:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) a sunny day b) a cloudy day c) a hot day d) a windy day Answer: The correct option is b) a cloudy day

At a hydro power plant:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) kinetic energy possessed by stored water is converted into electrical energy b) electricity is extracted from water c) water is converted into steam to turn turbines and produce electricity d)...

The part of box-type solar cooker which is responsible for producing greenhouse effect is:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) plane mirror reflector b) black coating inside the box c) glass sheet cover d) utensils placed in the cooker box Answer: The correct option is c) glass sheet cover

Solar cells are made of:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) conductors b) insulators c) semiconductors d) superconductors Answer: The correct option is c) semiconductors

The value of solar constant is:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) 1.4kWh b) 1.4kW/m c) 1.4kW/m2 d) 1.4kW/m3 Answer: The correct option is c) 1.4kW/m2

The radiations present in sunlight which make a solar cooker work are:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) visible light rays b) ultraviolet rays c) cosmic rays d) infrared rays Answer: The correct option is d) infrared rays

In order to make an efficient solar cooker, the cover of cooker box should be made of:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) transparent plastic sheet b) shining aluminum sheet c) butter paper sheet d) transparent glass sheet Answer: The correct option is d) transparent glass sheet

The minimum speed of wind necessary for the satisfactory working of a wind generator to produce electricity is about:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) 15km/h b) 25km/h c) 35km/h d) 45km/h Answer: The correct option is a) 15km/h

If the solar constant is 1.4 kW/m2 then solar energy received by 1 m2 area in one hour is: (a) 5040 J (b) 504.0 kJ (c) 5040 kJ (d) 5.04 kJ

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

The correct option is c) 5040kJ Given that $\begin{array}{l}\text { Solar constant }=1.4 \mathrm{~kW} / \mathrm{m}^{2}=1.4 \mathrm{~kJ} / \mathrm{s} / \mathrm{m}^{2} \quad\left(\text { converted }...

A solar cooker may not cook food if:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) the solar cooker is not placed in the shade b) the glass sheet cover of solar cooker is not closed c) a convex mirror reflector is not used d) the food containers of insulating material are not...

Which of the following is not an example of a biomass energy source?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) wood b) biogas c) atomic energy d) cow-dung Answer: The correct option is c) atomic energy

most of the sources of energy that we use represent stored solar energy. Which of the following is not ultimately derived from the sun’s energy?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) wind energy b) geothermal energy c) fossil fuels d) ethane Answer: The correct option is b) geothermal energy

The constituent of biogas which makes it an excellent fuel is:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) butane b) methane c) propane d) ethane Answer: The correct option is b) methane

The major component of biogas is:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) hydrogen b) butane c) hydrogen sulphide d) methane Answer: The correct option is d) methane

Which of the following is more environmentally friendly?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) burning of diesel b) burning of coal c) burning of charcoal d) burning of wood Answer: The correct option is c) burning of charcoal

Which of the following is not renewable energy technology?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) solar cells b) windmills c) nuclear power d) tidal power Answer: The correct option is c) nuclear power

The rise of sea-water during high tide is caused by the gravitational pull of the:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) sun b) earth c) moon d) mars Answer: The correct option is c) moon

One of the following is not required in the formation of biogas plant. This is:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) cow-dung b) water c) oxygen d) anaerobic bacteria Answer: The correct option is c) oxygen

The fuel which is not obtained from biomass is:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) firewood b) cow-dung cakes c) coke d) charcoal Answer: The correct option is c) coke

The non-renewable source of energy among the following is:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) hydroelectricity b) sewage gas c) natural gas d) gobar gas Answer: The correct option is c) natural gas\

Geothermal energy is produced by the:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) fission of radioactive materials b) burning of coal inside the coal mines c) combustion of natural gas deep inside the earth d) fusion of radioactive substance Answer: The correct option is a)...

The harnessing of which of the following leads to the destruction of large eco-systems?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) thermal power b) tidal power c) hydro power d) geothermal power Answer: The correct option is c) hydro power

Which of the following is not a consequence of establishing hydroelectric power plants?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) displacement of people b) production of methane c) occurrence of floods d) ecological disturbance Answer: The correct option is c) occurrence of floods

Which of the following is used as a moderator in the reactor of a nuclear power station?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) liquid sodium b) boron c) graphite d) carbon dioxide Answer: The correct option is c) graphite

The control rods used in the reactor of a nuclear power plant are made of:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) steel b) graphite c) uranium d) boron Answer: The correct option is d) boron

The ‘coolants’ which can be used in the reactor of a nuclear power station are:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) liquid mercury and nitrogen dioxide b) liquid sodium and carbon dioxide c) liquid ammonia and carbon monoxide d) liquid boron and uranium oxide Answer: The correct option is b) liquid sodium and...

In a nuclear power plant, coolant is a substance:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) which cools the hot, spent steam to condense it back to water b) which transfers heat from reactor to water in heat exchanger c) which is boiled to make steam to turn the turbine d) which cools...

Which of the following is ultimately not derived from the sun’s energy?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) wind energy b) nuclear energy c) biomass energy d) ocean thermal energy Answer: The correct option is b) nuclear energy

One atomic mass unit is equivalent to an energy of:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) 931 eV b) 9.31 MeV c) 1 MeV d) 931 MeV Answer: The correct option is d) 931 MeV

The energy in the reactor of a nuclear power station is produced by the process of:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) nuclear diffusion b) nuclear fission c) nuclear fusion d) nuclear fermentation Answer: The correct option is b) nuclear fission

One eV of nuclear energy is equivalent to:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) 1.6 × 10-14 J b) 1.6 × 10-12 J c) 1.6 × 10-19 J d) 1.6 × 10-13 J Answer: The correct option is c) 1.6 × 10-19 J

Which of the following can be produced during the nuclear fission as well as nuclear fusion reactions?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) protons b) deuterons c) electrons d) neutrons Answer: The correct option is d) neutrons

Nuclear fission reactions are not a source of energy for one of the following. This is:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) atom bomb b) power plants c) sun d) pacemaker Answer: The correct option is c) sun

The energy produced by converting 1 gram mass of a nuclear fuel into energy completely is:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) 9 × 1016 J b) 9 × 1014 J c) 9 × 1015 J d) 9 × 1013 J Answer: The correct option is d) 9 × 1013 J

The source of energy of the sun is:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) conversion of hydrogen gas into helium b) conversion of carbon fuel into carbon dioxide c) burning of hydrogen gas present in the sun d) disintegration of uranium into barium and krypton Answer:...

An uncontrolled nuclear chain reaction forms the basis of:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) nuclear power plant b) hydrogen bomb c) thermal power station d) atom bomb Answer: The correct answer is d) atom bomb

One MeV of nuclear energy is equivalent to:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) 1.6 × 10-13 J b) 1.6 × 10-19 J c) 1.6 × 10-16 J d) 1.6 × 10-15 J Answer: The correct option is a) 1.6 × 10-13 J Explanation: When an electron with a charge of 1.6 × 10-19 J Coulomb is accelerated...

One type of energy which has not been controlled so far is

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) ocean thermal energy b) nuclear fusion energy c) geothermal energy d) nuclear fission energy Answer: The correct option is b) nuclear fusion energy

The disposal of wastes produced in a nuclear power plant poses a big problem because it is:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) too heavy b) highly inflammable c) extremely foul smelling d) highly radioactive Answer: The correct option is d) highly radioactive

The heat energy released during nuclear fission and fusion is due to the:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) conversion of stored chemicals into energy b) conversion of momentum into energy c) conversion of mass into energy d) conversion of magnetism into energy Answer: The correct option is c)...

Which of the following can undergo nuclear fusion reaction?

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) uranium b) deuterium c) barium d) krypton Answer: The correct option is b) deuterium Deuterium is formed by the fusion of two Hydrogen atoms.

108 The major cause of environmental pollution is the use of:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) hydrogen as fuel b) biomass energy c) ocean energy d) fossil fuels Answer: The correct option is d) fossil fuels. Burning of fossil fuels results in the release of many harmful...

The world’s known coal reserves are expected to last for about:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) 200 years b) 400 years c) 500 years d) 100 years Answer: The correct option is a) 200 years

The fossil fuel whose known reserves in the earth are expected to last for the minimum period is:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) coal b) uranium c) petroleum d) natural gas Answer: The correct answer is c) petroleum because petroleum is a non renewable resource and it can't be replenished once exhausted...

An energy efficient device for producing light is:

CBSE, Class 10, Lakhmir Singh, Physics, Sources of Energy

a) DLF b) CFL c) FCL d) LPG Answer: The correct option b)...

Light of frequency 7.21 x $10^{14}$ Hz is incident in a metal surface. Electrons with a maximum speed of 6.0 x $10^{5}$ m/s are ejected from the surface. What is the threshold frequency for photoemission of electrons?

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

Frequency of the incident photon is given as $\mathbf{v}=488 \mathrm{~nm}=488 \times 10^{-9} \mathrm{~m}$Maximum speed of the electrons is given as $\mathbf{v}=6.0 \times 10^{5} \mathrm{~m} /...

The work function for a certain metal is 4.2 eV. Will this metal give photoelectric emission for incident radiation of wavelength 330 nm?

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

Work function of the metal is given as $\Phi_{o}=4.2 \mathrm{eV}$Charge on an electron, $\mathrm{e}=1.6 \times 10^{-19} \mathrm{C}$Planck's constant, $\mathrm{h}=\mathbf{6} .626 \times 10^{-34}...

A 100W sodium lamp radiates energy uniformly in all directions. The lamp is located at the centre of a large sphere that absorbs all the sodium light which is incident on it. The wavelength of the sodium light is 589 nm. (a) What is the energy per photon associated with the sodium light? (b) At what rate are the photons delivered to the sphere?

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

Power of the sodium lamp is given as $\mathbf{P}=\mathbf{1 0 0 W}$Wavelength of the emitted sodium light is given as $\lambda=589 \mathrm{~nm}$$$=589 \times 10^{-9} \mathrm{~m}$$Planck's constant,...

A uniform magnetic field of $1.5 \mathrm{~T}$ exists in a cylindrical region of a radius of $10.0 \mathrm{~cm}$ , its direction parallel to the axis along east to west. A wire carrying a current of $7.0$ A in the north to south direction passes through this region. What is the magnitude and direction of the force on the wire if, the wire in the N-S direction is lowered from the axis by a distance of $6.0 \mathrm{~cm} ?$

CBSE, Class 12, Moving Charges and Magnetism, NCERT, Physics

When the wire is lowered by $6 \mathrm{~cm}$, then Then, $x=\sqrt{(10)^{2}-\left(6^{2}\right)}=\sqrt{64}=8 \mathrm{~cm}$ $2 \mathrm{x}=\mathrm{I}_{2}=16 \mathrm{~cm}$ $F_{2}=BII_{2}$=$1.5 \times 7...

Answer the following question:
An electron travelling west to east enters a chamber having a uniform electrostatic field in the north to south direction. Specify the direction in which a uniform magnetic field should be set up to prevent the electron from deflecting from its straight-line path.

CBSE, Class 12, Moving Charges and Magnetism, NCERT, Physics

Because of the electric field, the negatively charged electron tends to go towards the north. The electron will not be deflected if an equal magnetic force acts in the other direction. We derive the...

A toroid has a core (non-ferromagnetic) of inner radius $25 \mathrm{~cm}$ and outer radius $26 \mathrm{~cm}$ , around which 3500 turns of a wire are wound. If the current in the wire is $11 \mathrm{~A}$ , what is the magnetic field in the empty space surrounded by the toroid.

CBSE, Class 12, Moving Charges and Magnetism, NCERT, Physics

The magnetic field in the empty space surrounded by the toroid is zero as it is non-ferromagnetic.

The wavelength of light from the spectral emission line of sodium is $589 \mathrm{~nm}$ . Find the kinetic energy at which (a) an electron, and (b) a neutron, would have the same de Broglie wavelength.

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

Wavelength of light of a sodium line is given as $\lambda=589 \mathrm{~nm}=589 \times 10^{-9} \mathrm{~m}$ Mass of an electron, $\mathrm{m}_{\mathrm{e}}=9.1 \times 10^{-31} \mathrm{Kg}$ Mass of a...

What is the De Broglie wavelength of an electron with a kinetic energy of $120 \mathrm{eV} .$

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

de Broglie wavelength of an electron having a momentum $p$, is given by the relation: $\lambda=\frac{h}{p}$ $=\frac{6.6 \times 10^{-34}}{5.91 \times 10^{-24}}=1.116 \times 10^{-10} \mathrm{~m}=0.112...

What is the: (a) Momentum, (b) Speed of an electron with a kinetic energy of $120 \mathrm{eV} .$

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

Kinetic energy of the electron is given as $\mathbf{E}_{\mathrm{K}}=\mathbf{1 2 0} \mathrm{eV}$ Planck's constant, $\mathbf{h}=\mathbf{6 . 6} \times \mathbf{1 0}^{-34} \mathrm{~J} \mathrm{~s}$ Mass...

Calculate the (a) momentum, and (b) the de Broglie wavelength of the electrons accelerated through a potential difference of $56 \mathrm{~V}$ .

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

Potential difference is given in the question as $\mathbf{V}=\mathbf{5 6 V}$ Planck's constant, $\mathbf{h}=6.6 \times 10^{-34} \mathrm{~J} \mathrm{~s}$ Mass of an electron, $\mathbf{m}=\mathbf{9 ....

Light of wavelength $488 \mathrm{~nm}$ is produced by an argon laser which is used in the photoelectric effect. When light from this spectral line is incident on the emitter, the stopping (cut-off) potential of photoelectrons is $0.38 \mathrm{~V}$ . Find the work function of the material from which the emitter is made.

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

Wavelength of light produced by the argon laser is given as $\lambda=488 \mathrm{~nm}=488 \times 10^{-9} \mathrm{~m}$ Stopping potential of the photoelectrons is given as...

Light of frequency $7.21 \times 10^{14} \mathrm{~Hz}$ is incident in a metal surface. Electrons with a maximum speed of $6.0 \times 10^{5} \mathrm{~m} / \mathrm{s}$ are ejected from the surface. What is the threshold frequency for photoemission of electrons?

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

Frequency of the incident photon is provided as $v=488 \mathrm{~nm}=488 \times 10^{-9} \mathrm{~m}$ Maximum speed of the electrons is $\mathbf{v}=\mathbf{6 . 0} \times \mathbf{1 0}^{5} \mathrm{~m} /...

The work function for a certain metal is $4.2 \mathrm{eV} .$ Will this metal give photoelectric emission for incident radiation of wavelength 330 nm?

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

Work function of the metal is given as $\Phi_{o}=4.2 \mathrm{eV}$ Charge on an electron is $\mathbf{e}=\mathbf{1 . 6} \times \mathbf{1 0}^{-19} \mathbf{C}$ Planck's constant, $\mathbf{h}=\mathbf{6 ....

The threshold frequency for a certain metal is $3.3 \times 10^{14} \mathrm{~Hz}$ . If the light of frequency $8.2 \times 10^{14} \mathrm{~Hz}$ is incident on the metal, predict the cut-off voltage for the photoelectric emission.

Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

Threshold frequency of the metal given to us is $\mathbf{v}_{\mathbf{0}}=\mathbf{3 . 3} \times \mathbf{1 0}^{\mathbf{1 4}} \mathrm{Hz}$. Frequency of light incident on the metal is given as...

A $100 \mathrm{~W}$ sodium lamp radiates energy uniformly in all directions. The lamp is located at the centre of a large sphere that absorbs all the sodium light which is incident on it. The wavelength
of the sodium light is $589 \mathrm{~nm} .$ (a) What is the energy per photon associated with the sodium light? (b) At what rate are the photons delivered to the sphere?

CBSE, Class 12, Dual Nature of Radiation and Matter, Guides, NCERT, Physics

Power of the sodium lamp is given as $\mathbf{P}=\mathbf{1 0 0 W}$ Wavelength of the emitted sodium light is given as $\lambda=589 \mathrm{~nm}$ $=589 \times 10^{-9} \mathrm{~m}$ Planck's constant,...

In an experiment on the photoelectric effect, the slope of the cut-off voltage versus frequency of incident light is found to be $4.12 \times 10^{-15} \mathrm{~V} \mathrm{~s} .$ Calculate the value of Planck’s constant.

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

The slope of cut-off voltage (V) versus frequency (v) is given as, $\frac{V}{v}=4.12 \times 10^{-15} \mathrm{Vs}$ $\mathrm{V}$ and frequency is related by the equation: $\mathrm{Hv}=\mathrm{eV}$...

The energy flux of sunlight reaching the surface of the earth is $1.388 \times 10^{3} \mathrm{~W} / \mathrm{m}^{2}$ . How many photons are incident on the Earth per second/square meter? Assume an average wavelength of $550 \mathrm{~nm}$

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

Energy flux of sunlight reaching the surface of the earth: $\phi=1.388 \times 10^{3} \mathrm{~W} / \mathrm{m}^{2}$ Hence, power of sunlight per square metre, $\mathbf{P}=\mathbf{1 . 3 8 8} \times...

Why is there a need to harness non-conventional sources of energy? Give two main reasons.

Biology, CBSE, Class 10, Exercise 1, NCERT, Science, Sources of Energy

Reasons for the need to harness non-conventional sources of energy: 1. The conventional sources are the source of energy which is depleted and will soon wear out. 2. The non-conventional energy...

Choose the correct statement

Biology, CBSE, Class 10, NCERT, Science, Sources of Energy

(a) Sun can be taken as an inexhaustible source of energy (b) There is infinite storage of fossil fuel inside the earth (c) Hydro and wind energy plants are non-polluting sources of energy (d) Waste...

Acid rain happens because

Biology, CBSE, Class 10, NCERT, Science, Sources of Energy

(a) sun leads to heating of the upper layer of the atmosphere (b) burning of fossil fuels release oxides of carbon, nitrogen and sulphur in the atmosphere (c) electrical charges are produced due to...

A student-focussed the image of a candle flame on a white screen using a convex lens. He noted down the position of the candle screen and the lens as under

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

Position of candle = 12.0 cm Position of convex lens = 50.0 cm Position of the screen = 88.0 cm What is the focal length of the convex lens?Where will the image be formed if he shifts the candle...

Define power of a lens. What is its unit? One student uses a lens of focal length 50 cm and another of –50 cm. What is the nature of the lens and its power used by each of them?

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

Power of lens Is the degree of convergence and divergence provided by a lens and its unit is Diopter (D). The focal length of the lens used by the first student is in positive so it is a convex...

Size of the image of an object by a mirror having a focal length of 20 cm is observed to be reduced to 1/3rd of its size. At what distance the object has been placed from the mirror? What is the nature of the image and the mirror?

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

Given, m = 1/3 Using = 1/v+1/u=1/f Calculating u, u = – 80 cm. The image is real and inverted so the mirror is concave.

The image of a candle flame formed by a lens is obtained on a screen placed on the other side of the lens. If the image is three times the size of the flame and the distance between the lens and image is 80 cm, at what distance should the candle be placed from the lens? What is the nature of the image at a distance of 80 cm and the lens?

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

Ray Diagram The image in the screen is real and so, the magnification is, m = –3 v = 80 cm u = ? m = v/u –3 = 80/u u = –80/3 cm As we know, 1/f = 1/v – 1/u =1/80 + 3/80 = 4/80 =...

Draw ray diagrams showing the image formation by a convex mirror when an object is placed

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

(a) at infinity (b) at a finite distance from the mirror (a) (b)

Draw ray diagrams showing the image formation by a concave lens when an object is placed

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

(a) at the focus of the lens (b) between focus and twice the focal length of the lens (c) beyond twice the focal length of the lens (a) (b) (c)

Write laws of refraction. Explain the same with the help of a ray diagram, when a ray of light passes through a rectangular glass slab.

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

The Laws of refraction: The Incident ray, refracted ray and the normal at the point of incidence lies in the same plane. The ratio of the sine of incidence and sine of refraction is same for the...

Draw ray diagrams showing the image formation by a convex lens when an object is placed

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

(a) between optical centre and focus of the lens (b) between focus and twice the focal length of the lens (c) at twice the focal length of the lens (d) at infinity (e) at the focus of the lens (a)...

Draw ray diagrams showing the image formation by a concave mirror when an object is placed

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

(a) between pole and focus of the mirror (b) between focus and centre of curvature of the mirror (c) at the centre of curvature of the mirror (d) a little beyond the centre of curvature of the...

Draw a ray diagram showing the path of rays of light when it enters with oblique incidence

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

1. From air into water; 2. From water into air. 1. 2.

Under what condition in an arrangement of two plane mirrors, incident ray and reflected ray will always be parallel to each other, whatever may be the angle of incidence. Show the same with the help of a diagram.

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

When two plane mirrors are placed perpendicular to each other, then the Incident ray and the reflected ray will always be parallel to each other.

How are power and focal length of a lens related? You are provided with two lenses of focal length 20 cm and 40 cm respectively. Which lens will you use to obtain more convergent light?

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

The power of lens is inversely proportional to the focal length of the lens and the lens with focal length 20 has more power when compared to a lens with a focal length of 40 cm. The lens having...

Refractive index of diamond with respect to glass is 1.6 and the absolute refractive index of glass is 1.5. Find out the absolute refractive index of diamond.

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

Given, Absolute RI of diamond= 1.6 Absolute RI of glass= 1.5 Thus, Absolute refractive index of diamond = 2.4

Sudha finds out that the sharp image of the window pane of her science laboratory is formed at a distance of 15 cm from the lens. She now tries to focus the building visible to her outside the window instead of the window pane without disturbing the lens. In which direction will she move the screen to obtain a sharp image of the building? What is the approximate focal length of this lens?

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

To get a clear picture of the structure, Sudha has to move the screen and remove the lens. The length of the area will be about 15 cm. The light rays from a distant object such as a tree or a...

A convex lens of focal length 20 cm can produce a magnified virtual as well as real image. Is this a correct statement? If yes, where shall the object be placed in each case for obtaining these images?

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

When an object is in F and F2 of a convex lens. So, we need to place the object between 20 and 40 cm of the lens. When an object is placed between F and 0 of a convex lens, its magnified, vertical...

How is the refractive index of a medium related to the speed of light? Obtain an expression for the refractive index of a medium with respect to another in terms of speed of light in these two media?

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

The Refractive Index can be seen as a factor in reducing the speed and length of radiation in relation to vacuum values. w = civ where, n- Refractive index c – Speed of light v- Velocity The ratio...

A pencil, when dipped in water in a glass tumbler, appears to be bent at the interface of air and water. Will the pencil appear to be bent to the same extent, if instead of water we use liquids like, kerosene or turpentine. Support your answer with reason.

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

The bending of light here is a reversal function. Reversal is based on refractive indices. The opposing indices of paraffin or turpentine will not be the same as water. So the degree of bending will...

Why does a light ray incident on a rectangular glass slab immersed in any medium emerges parallel to itself? Explain using a diagram.

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

When light ray penetrates into the denser medium from the abnormal bend to the normal In this case the magnitude of the curvature of the parallel radiation is the same. Thus, the emergent ray is...

Identify the device used as a spherical mirror or lens in the following cases, when the image formed is virtual and erect in each case.

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

1. Object is placed between the device and its focus, an image formed is enlarged and behind it. 2. Object is placed between the focus and device, an image formed is enlarged and on the same side as...

In which of the following, the image of an object placed at infinity will be highly diminished and point sized?

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

(a) Concave mirror only (b) Convex mirror only (c) Convex lens only (d) Concave mirror, convex mirror, concave lens and convex lens Answer: (d) Concave mirror, convex mirror, concave lens and convex...

A child is standing in front of a magic mirror. She finds the image of her head bigger, the middle portion of her body of the same size and that of the legs smaller. The following is the order of combinations for the magic mirror from the top.

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

(a) Plane, convex and concave (b) Convex, concave and plane (c) Concave, plane and convex (d) Convex, plane and concave Answer: (c) Concave, plane and convex Explanation: Concave mirror showed her...

Which of the following ray diagrams is correct for the ray of light incident on a lens shown in the figure?

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

(a) Fig. A. (b) Fig. B. (c) Fig. C. (d) Fig. D. Answer: (a) Fig. A. Explanation: The ray diagram in figure A is correct for the light ray incident on a lens as the incident ray travels through the...

You are given water, mustard oil, glycerine and kerosene. In which of these media a ray of light incident obliquely at same angle would bend the most?

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

(a) Kerosene (b) Water (c) Mustard oil (d) Glycerine Answer: (d) Glycerine Explanation: A ray of light incident obliquely at same angle would bend the most in glycerine media.

Which of the following ray diagrams is correct for the ray of light incident on a concave mirror as shown in the figure?

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

LRR PIC 6----- (a) Fig. A (b) Fig. B (c) Fig. C (d) Fig. D Answer: (d) Fig. D Explanation: The ray diagram in Figure D is correct for the ray of light incident on a concave mirror as the incident is...

The path of a ray of light coming from air passing through a rectangular glass slab traced by four students are shown as A, B, C and D in the Figure. Which one of them is correct?

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

(a) A (b) B (c) C (d) D Answer: b) B Explanation: The path of a ray of light coming from air passing through a rectangular glass slab traced by the student B is correct.

The laws of reflection hold good for

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

(a) plane mirror only (b) concave mirror only (c) convex mirror only (d) all mirrors irrespective of their shape Answer: (d) all mirrors irrespective of their shape Explanation: The laws of...

In torches, searchlights and headlights of vehicles the bulb is placed

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

(a) between the pole and the focus of the reflector (b) very near to the focus of the reflector (c) between the focus and centre of curvature of the reflector (d) at the centre of curvature of the...

A full-length image of a distant tall building can definitely be seen by using

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

(a) a concave mirror (b) a convex mirror (c) a plane mirror (d) both concave as well as plane mirror Answer: (b) a convex mirror Explanation: A full-length image of a distant tall building can...

Rays from Sun converge at a point 15 cm in front of a concave mirror. Where an object should be placed so that size of its image is equal to the size of the object?

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

(a) 15 cm in front of the mirror (b) 30 cm in front of the mirror (c) between 15 cm and 30 cm in front of the mirror (d) more than 30 cm in front of the mirror Answer: (d) more than 30 cm in front...

Magnification produced by a rearview mirror fitted in vehicles

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

(a) is less than one (b) is more than one (c) is equal to one (d) can be more than or less than one depending upon the position of the object in front of it Answer: (a) is less than one Explanation:...

Which of the following statements is true?

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

(a) A convex lens has 4 dioptre power having a focal length 0.25 m (b) A convex lens has –4 dioptre power having a focal length 0.25 m (c) A concave lens has 4 dioptre power having a focal length...

A beam of light is incident through the holes on side A and emerges out of the holes on the other face of the box as shown in the figure. Which of the following could be inside the box?

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

(a) Concave lens (b) Rectangular glass slab (c) Prism (d) Convex lens Answer: (d) Convex lens Explanation: When a beam of light is incident through the holes on side A and emerges out of the holes...

Beams of light are incident through the holes A and B and emerge out of the box through the holes C and D respectively as shown in the Figure. Which of the following could be inside the box?

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

(a) A rectangular glass slab (b) A convex lens (c) A concave lens (d) A prism Answer: (a) A rectangular glass slab Explanation: When the beams of light are incident through the holes A and B and...

A light ray enters from medium A to medium B as shown in the Figure. The refractive

CBSE, Class 10, Light Reflection and Refraction, Light Reflection and Refraction, NCERT, Physics

index of medium B relative to A will be (a) greater than unity (b) less than unity (c) equal to unity (d) zero Answer: (a) greater than unity Explanation: The refractive index is the bending of a...

The figure shows a ray of light as it travels from medium A to medium B. Refractive index of the

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

medium B relative to medium A is (a) √3 / √2 (b) 2 / 3 (c) 1/ 2 (d) 2 Answer: (a) √3 / √2 Explanation: According to the Snell’s law, the refractive index of the medium B relative to the medium A is...

Under which of the following conditions a concave mirror can form an image larger than the actual object?

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

(a) When the object is kept at a distance equal to its radius of curvature (b) When an object is kept at a distance less than its focal length (c) When an object is placed between the focus and...

A 10 mm long awl pin is placed vertically in front of a concave mirror. A 5 mm long image of the awl pin is formed at 30 cm in front of the mirror. The focal length of this mirror is

CBSE, Class 10, Light Reflection and Refraction, NCERT, Physics

(a) – 30 cm (b) – 20 cm (c) – 40 cm (d) – 60 cm Answer: (b) – 20 cm Explanation: In this case, the focal length of the concave mirror is – 20 cm.

Which of the following can make a parallel beam of light when light from a point source is incident on it?

CBSE, Class 10, Guides, Light Reflection and Refraction, NCERT, Physics

(a) Concave mirror as well as convex lens (b) Convex mirror as well as a concave lens (c) Two plane mirrors placed at 90° to each other (d) Concave mirror as well as a concave lens Answer: (d)...

Monochromatic light of wavelength $632.8 \mathrm{~nm}$ is produced by a helium-neon laser. The power emitted is $9.42 \mathrm{~mW}$ . How fast does a hydrogen atom have to travel in order to have the same momentum as that of the photon?

Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

We are provided that the momentum of the hydrogen atom is equal to the momentum of the photon, $\mathrm{P}=1.047 \times 10^{-27} \mathrm{~kg} \mathrm{~m} / \mathrm{s}$ Momentum's expression is: $P=m...

Monochromatic light of wavelength $632.8 \mathrm{~nm}$ is produced by a helium-neon laser. The power emitted is $9.42 \mathrm{~mW}$ (a) Find the energy and momentum of each photon in the light beam
(b) How many photons per second, on the average, arrive at a target irradiated by this beam? (Assume the beam to have a uniform cross-section which is less than the target area)

Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

Wavelength of a monochromatic light is given as $\lambda=632.8 \mathrm{~nm}=632.8 \times 10^{-9} \mathrm{~m}$ Power emitted by the laser is, $P=9.42 \mathrm{~mW}=9.42 \times 10^{-3} \mathrm{~W}$...

The photoelectric cut-off voltage in a certain experiment is $1.5 \mathrm{~V} .$ What is the maximum kinetic energy of photoelectrons emitted?

CBSE, Class 12, Dual Nature of Radiation and Matter, Physics

Photoelectric cut-off voltage is given as $\mathbf{V}_{\mathbf{0}}=\mathbf{1 . 5} \mathbf{V}$ The maximum kinetic energy for emitted photoelectrons, $K_{e}=eV$ Where, $e=$ charge on an electron...

The work function of caesium metal is $2.14 \mathrm{eV} .$ When light of frequency $6 \times 10^{14} \mathrm{~Hz}$ is incident on the metal surface, photoemission of electrons occurs. What is the maximum speed of the emitted photoelectrons?

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

$\mathbf{v}$ is the maximum speed of photoelectrons emittedThe kinetic energy relation can be written as:$$\mathrm{K}=\frac{1}{2} m v^{2}$$Where,$$\mathrm{m}=\text { mass of electron }=9.1 \times...

The work function of caesium metal is $2.14 \mathrm{eV} .$ When light of frequency $6 \times 10^{14} \mathrm{~Hz}$ is incident on the metal surface, photoemission of electrons occurs. What is the (a) maximum kinetic energy of the emitted electrons (b) Stopping potential

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

Work function of caesium is given as $\Phi_{o}=2.14 \mathrm{eV}$ Frequency of light is given as $\mathbf{v}=6.0 \times 10^{14} \mathrm{~Hz}$ (a) The maximum energy (kinetic) by the photoelectric...

Find the: (a) Maximum frequency, and (b) The minimum wavelength of X-rays produced by $30 \mathrm{kV}$ electrons.

CBSE, Class 12, Dual Nature of Radiation and Matter, NCERT, Physics

Electron potential is given as $\mathrm{V}=30 \mathrm{kV}=\mathbf{3} \times \mathbf{1 0}^{4} \mathrm{~V}$ Hence, electron energy will be $\mathbf{E}=\mathbf{3} \times \mathbf{1 0}^{4} \mathrm{eV}$...

A galvanometer coil has a resistance of $15 \Omega$ and the metre shows full-scale deflection for a current of 4 mA. How will you convert the metre into an ammeter of range 0 to 6 A?

CBSE, Class 12, Moving Charges and Magnetism, Physics

Resistance of the galvanometer is given as $\mathrm{G}=15 \Omega$ Current flowing through the galvanometer is given as $\mathrm{lg}=4 \mathrm{~mA}=4 \times 10^{-3} \mathrm{~A}$ Ammeter range is $0$...