Previous Year Question Papers

### Calculate the threshold frequency of photon for photoelectric emission from a metal of work function .

Ans: Given is the work function $0.1 \mathrm{eV}$, $$\phi_{o}=h v_{0}$$ Class 12 Physics $\underline{\text { wuw. vedantu.com }}$ 1 $10 a-x=10 a-2.5 a=7.5 a$ from charge $9 q$

### A straight wire carries a current of . An electron moving at is at distance from the wire. Find the force acting on the electron if its velocity is directed towards the wire.

Ans: We are given the current through the straight wire to be, $I=10 \mathrm{~A}$ Speed of the electron, $\mathrm{v}=10^{7} \mathrm{~m} / \mathrm{s}$ Distance of electron from the wire,...

### Give one difference each between diamagnetic and ferromagnetic substances. Give one example of each.

Ans: Diamagnetic substances are the ones that are weakly repelled by a magnet. For example, gold. Ferromagnetic materials are the ones that are strongly attracted by a magnet. For example, iron.

### A steady current flows in the network What will be the magnetic field at the center of the network?

Ans: The magnetic field at the center of the network is zero. This is because, magnetic field at the center of the loop would just equal and opposite $i . e .$, magnetic field due PQR is equal and...

### A cyclotron is not suitable to accelerate electron. Why?

Ans: A cyclotron is not suitable to accelerate electron as its mass is known to be less due to which they gain speed and step out of the dee immediately,

### Two wires of equal lengths are bent in the form of two loops. One of the loops is square shaped whereas the other loop is circular. These are suspended in a uniform magnetic field and the same current is passed through them. Which loop will experience greater torque? Give reasons.

Ans: We know the expression for torque as, $$\begin{array}{l} \tau=\mathrm{NIAB} \\ \Rightarrow \tau \propto \mathrm{A} \end{array}$$ Since, we know that the area of circular loops is more than...

### What will be the path of a charged particle moving along the direction of a uniform magnetic field?

Ans: The path of a charged particle moving along the direction of a uniform magnetic field would be a straight line path as no force would act on the particle.

### State two properties of the material of the wire used for suspension of the coil in a moving coil galvanometer.

Ans: Two properties of the material of the wire used for suspension of the coil in a moving coil galvanometer are: i. Non-Brittle conductor ii. Restoring Torque per unit twist should be small.

### V.I graph for a metallic wire at two different temperatures Which of these two temperatures is higher and why?

Ans: From the graph: Slope $=\frac{\mathrm{i}}{\mathrm{V}}$ It is known that, $\frac{i}{V}=\frac{1}{R}$ It means that the smaller the slope, the larger the resistance.

### A stream of electrons travelling with speed at right angles to a uniform electric field is deflected in a circular path of radius Prove that

Ans: The path of the electron that is travelling with velocity $\mathrm{vm} / \mathrm{s}$ at right angle of $\bar{E}$ is of circular shape. It requires a centripetal in nature, $F=\frac{m v^{2}}{r}$...

### If the amount of electric flux entering and leaving a closed surface are and respectively. What is the electric charge inside the surface?

Ans: Net flux can be given as $=\phi_{2}-\phi_{1}$ Since $\phi=\frac{q}{\epsilon_{0}}$ $$\Rightarrow \mathrm{Q}=\left(\phi_{2}-\phi_{1}\right) \in_{0}$$ The electric charge inside the surface can...

### Draw one equipotential surfaces (1) Due to uniform electric field (2) For a point charge

Ans: The diagrams are given as: Equipoterhibil Surfaces 3 $\mathrm{~ ( 2 c ) r o m}$

### What happens to the capacitance of a capacitor when a dielectric slab is placed between its plates?

Ans: The introduction of dielectric in a capacitor will reduce the effective charge on plate and therefore will increase the capacitance.

### The plates of a charged capacitor are connected by a voltmeter. If the plates of the capacitor are moved further apart, what will be the effect on the reading of the voltmeter?

Ans: The relation between capacitance, area, distance and dielectric constant is $$C=\frac{A E_{0}}{d} \Rightarrow C \propto \frac{1}{d}$$ Hence, if distance increases, capacitance decreases....

### The distance of the field point on the equatorial plane of a small electric dipole is halved. By what factors will the electric field due to the dipole changes?

Ans: The formula $E x \frac{1}{r^{3}}$ gives the relation between electric field and distance. $$\therefore E \propto \frac{1}{\left(\frac{r}{2}\right)^{3}} \Rightarrow E \propto \frac{8}{r^{3}}$$...

### Force of attraction between two point electric charges placed at a distance d in a medium is . What distance apart should these be kept in the same medium, so that force between them becomes ?

Ans: If two point charges are $q_{1}$ and $q_{2}$ separated by distance $d$, it can be expressed as: $\mathrm{F}=\frac{\mathrm{Kq}_{1} \mathrm{q}_{2}}{\mathrm{~d}^{2}}$ Suppose if force becomes...

### What is the work done in moving a point change from corner to corner of a square when a charge exists at the centre of the square?

Ans: Point $A \& B$ are at the same distance from the point $O$. Hence,

### Why does the electric field inside a dielectric decrease when it is placed in an external electric field?

Ans: The electric field that is present inside a dielectric decreases when it is placed in an external electric field because of polarisation as it creates an internal electric field which is...

### If the net outward flux through the surface of the box were zero, could you conclude that there were no charges inside the box? Why or why not?

Ans: No. The net flux entering out through a body depends on the net charge contained in the body. If the net flux is given to be zero, then it can be inferred that the net charge inside the body is...

### Careful measurement of the electric field at the surface of a black box indicate that the net outward flux through the surface of the box is a) What is the net charge inside the box?

Ans: It is given that: Net outward flux through surface of the box, $\phi=8.0 \times 10^{3} \mathrm{Nr}^{2} / \mathrm{C}$. For a body containing net charge a, flux is given by...

### What is the net flux of the uniform electric field of exercise through a cube of side oriented so that its faces are parallel to the coordinate planes?

Ans: It is given that all the faces of the cube are parallel to the coordinate planes. Clearly, the number of field lines entering the cube is equal to the number of field lines entering out of the...

### When a glass rod is rubbed with a silk cloth, charges appear on both. A similar phenomenon is observed with many other pairs of bodies. Explain how this observation is consistent with the law of conservation of charge. Ans: Rubbing is a phenomenon in which there is production of charges equal in

Ans: Since unlike charges attract and like charges repel each other, the particles 1 and 2 moving towards the positively charged plate are negatively charged whereas the particle 3 that moves...

### Why can one ignore the quantization of electric charge when dealing with macroscopic i.e., large scale charge?

Ans: When dealing with macroscopic or large-scale charges, the charges used are huge in number as compared to the magnitude of electric charge. Hence, the quantization of electric charge is of no...

### An electric dipole when held at with respect to a uniform electric field of experiences a torque of . Calculate dipole moment of the dipole?

Ans: It is given that $$\begin{array}{l} \theta=30^{\circ} \\ \tau=9 \times 10^{-26} \mathrm{Nm} \\ E=10^{4} \mathrm{~N} / \mathrm{C} \end{array}$$ Dipole moment P needs to be calculated. It is...

### How is the rise of liquid affected if the top of the capillary is closed?

If the top of the capillary tube is closed, there will be a little rise in the capillary tube. Because the downward force exerted by compressed air above the liquid in the tube opposes the rise of...

### The liquid rises in capillary tube when the angle of contact is i) obtuse angle ii) acute angle iii) radian iv) radian.

Correct option is ii) acute angle Liquid rises in a capillary tube if the angle of contact is acute, but liquid falls in a capillary tube if the angle of contact is obtuse

### Write chromyl chloride test with equation

Chloride radical is detected by the chromyl chloride test. In this test, chromyl chloride gas (orange red color) is produced. Equation Involved – 4NaCl + K2Cr2O7 + 6H2SO4 → 4NaHSO4 + 2KHSO4 + 3H2O +...

### What do you understand by lanthanide contraction

The lanthanide contraction is the decrease in the atomic or ionic radii with increase in the atomic number of lanthanides

### What are lanthanide elements?

Lanthanide elements resembles a lot in properties with lanthanum. Lanthanide is group of 14 elements from atomic number 58 to 71. In these elements on increasing atomic number electron enters into...

### Explain oxidization properties of potassium permanganate in acidic medium.

2KMnO4 + 8H2SO4 + 10KI → 6K2SO4 + 8H2O + 5I2 2KMnO4 + 5SO2 + 2H2O → 2MnSO4 + 2H2SO4 + K2SO4 2KmO4 + 16HCl → 2KCl + 2MnCl2 + 8H2O + 5Cl2 5COOH – COOH + [5O] → 10CO2 + 5H2O

### Why depletion of ozone layer threat to us ?

The ozone layer's depletion has negative consequences for the environment. Let's look at the key consequences of ozone depletion on humans and the environment. Human Health Effects Due to the ozone...

### How are water and minerals transported in plants?

The Xylem transports water and minerals in plants. - Root hairs are hairs that grow on a plant's roots. Because they are in close touch with the water layer between the soil particles, these root...

### What are the functions of digestive enzymes ?

Enzymes are proteins with specific functions. They're found in all living cells and are required for every chemical reaction that takes place in the body. Each enzyme is responsible for a specific...

### Mention two differences between ‘Artery’ and ‘Vein’.

One of the fundamental differences between arteries and veins is that arteries deliver oxygenated blood to all body areas, whereas veins, with the exception of pulmonary arteries and veins, carry...

### What happens when metals react with water?

When a metal reacts with water, a metal hydroxide is generated, as well as hydrogen gas. The chemical reactivity of a metal determines the degree of its interaction with water. Some metals respond...

### write the valency of magnesium ?

The valency of magnesium is 2.

### Write balanced chemical equations for the reation taking place when – (A) Dilute Sulphuric acid reacts with Zinc

H2SO4(aq)+Zn(s)→ZnSO4(aq)+H2(g)

### What do you mean by a precipitation reaction?

In our daily lives, we see a lot of chemical reactions. Burning, corrosion, food heating, and digestion are all instances of such interactions. Precipitation reactions are a common type of chemical...

### What is electric power? Derive , where is the amount of heat produced by steady curnent I through a resistor in time t.

Electric power is the rate at which electrical energy is transferred by an electric circuit per unit of time. The watt, or one joule per second, is the SI unit of power. Electric generators are the...

### Draw a labelled diagram of an electric motor. Explain its principle and working. What is the function of split ring in an electric motor?

In an electric motor, electrical energy is turned into mechanical energy. Electric motor operation: When a current is fed through the coil PQRS, the coil begins to rotate anticlockwise because a...

### Why two magnetic lines of force do not intersect each other?

The intensity of the magnetic lines is constant throughout and proportional to their proximity. Reason - The two magnetic field lines do not connect because if they did, the compass needle would...

### Why are we looking at alternate sources of energy?

They are long-term. The renewable energy basis in the United States is practically intact, from the sun to wind to biofuels. And, because these alternative energy sources are regenerated organically...

### why does the sun appear reddish during sunrise?

At the time of sunset or sunrise, the Sun and its surroundings appear red because of the scattering of light. At the time of sunset or sunrise, the light rays from the Sun have to travel a long...

### Why is the series arrangement not used for domestic circuit?

The quantity of current in a serial circuit reduces when each component receives a low voltage, causing the gadget to become heated and malfunction. As a result, in home circuits, the series layout...

### State the laws of refraction of light.

According to refraction laws, At the point of incidence, the incident ray, refracted ray, and normal to the interface of two media all lie on the same plane. A constant is the ratio of the sine of...

### With the help of an experiment show that chlorophyll is essential for photosynthesis.

1. We'll start with a potted plant like a croton, which has partially green and partially white leaves. Chlorophyll is present in the green portion of the leaf, but not in the white portion. 2....

### What is the role of decomposers in the ecosystem?

Decomposers have a variety of roles in the ecosystem: they decompose biodegradable substances into usable chemicals; they release nutrients into the soil by dissolving dead and decaying waste,...

### What are the benefits of sexual reproduction in comparison to asexual reproduction?

The benefits of sexual reproduction include the generation of genetic variety in the progeny. Because of their diversity, the species can adapt to different habitats, giving them a survival...

### What do you understand by elevation of boiling point and molal elevation constant, with the help of this constant how can you find the molecular mass of non-volatile solute

The elevation of boiling point on adding one mole solute to 1000 g solvent is called molal boiling point elevation constant. It is denoted by Kb. Its unit is K kg mol-1. The elevation of boiling...

### Define excretion. What are excretory products?

Excretion is a vital life mechanism that is observed in all living organisms. Excretory products are produced as a result of both metabolic and non-metabolic processes. Animal wastes are divided...

### Give the names of active ingredients and their one use of the following medicinal plants. (i) Amla (ii) Haldi (iii) Tulsi

(i) Vitamin C – Cures fever, asthma and diabetes. (ii) Curcumin – Used as an antiseptic and antibiotic. (iii) Cineole and Eugenol – Cures skin diseases, ear pain, cough and cold

### Write any two differences between respiration and combustion.

The process through which nutrients are transformed into useable energy in a cell is known as cellular respiration. It's a biological process in which energy is released in stages as chemical...

### Write short notes on Sushrut

Sushrut was a renowned surgeon of ancient India and author of the book Sushrut Samhita. He was the first physician to advocate what is today known as 'Caesarean operation'. He was also expert in...

### What is photosynthesis ? Wnte its chemical equation.

The following is the photosynthesis equation: C6H12O6 + 6O2 = 6CO2 + 6H20 + (energy) Glucose and oxygen are made from carbon dioxide, water, and light energy.

### What steps are important for forest conservation ?

Other key methods for forest conservation include: Legislation prohibiting the legislature from cutting down trees indiscriminately. Willingness of the government to prevent deforestation by...

### Write the equation for the reaction of Plaster of Paris with water.

CaSO4.1/2H2O + 3/2H2O = CaSO4.2H2O is the chemical equation for the reaction of Plaster of Paris and water. Heat is released when plaster of Paris reacts with water and crystallises. Plaster of...

### Give two names of artificial sweeteners

Aspartame and Saccharin

### Water is liquid while hydrogen sulphide is a gas at normal temperature. Why?

In water, the oxygen is electronegative due to the intermolecular hydrogen bonding which is formed in the water molecules and exists in a liquid state. Whereas, the sulphur is less electronegative...

### Write prevention (two) of corrosion

Prevention of Corrosion: (i) By coating metal surface with oil or grease: A thin layer of oil or grease is coated on the surface of the metal. (ii) By painting the metal surface: A layer of point is...

### Write electrochemical theory of corrosion

Electrochemical theory of corrosion: A number of galvanic cells are formed in impure iron. In rusting of iron pure iron acts as an anode while impure part of iron acts as a cathode. A thin layer...

### What do you understand by corrosion?

Corrosion is defined as the process by which the layers of undesired compounds are formed on the surface of the metal when exposed to the atmospheric conditions

### 10.07 gram of silver is obtained during the circulations of electric of 5 ampere upto 30 minutes in silver nitrate pot (cell). Find out electrochemical equivalent of silver. If chemical equivalent of hydrogen is 0.00001036 then will be equivalent weight of silver

Faraday’s first law of electrolysis states that the amount of any substance deposited or liberated at any electrode is directly proportional to the quantity of electricity passed through the...

### What happens when: (i) Ammonia reacts with formaldehyde (ii) Acetic acid reacts with PCl5

(i) Urotropine is formed when ammonia reacts with formaldehyde. 6HCHO + 4NH3 → (CH2) 6N4 + 6H2O (ii) Acetyl chloride is produced when acetic acid reacts with PCl5. CH3COOH + PCl5 → CH3COCl + POCl3 +...

### What happens when: (i) Acetyl chloride is reduced with hydrogen in presence of barium sulphate associated with palladium. (ii) Benzaldehyde boils with 45% NaOH

(i) Acetaldehyde is obtained when acetyl chloride is reduced with hydrogen in presence of barium sulphate associated with palladium. CH3 – COCl + 2H → CH3CHO + HCl (ii) Sodium benzoate and Benzoyl...