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 $9 q$

### What is the Brewster angle for air to glass transition? (Refractive index of glass )

Ans: We are given the refractive index of glass to be, $\mu=1.5$ BreWster angle $=\theta$ Brewster angle is known to be related to refractive index as: $$ \begin{array}{l} \tan \theta=\mu \\...

### At a certain location in Africa, a compass points west of the geographic north. The north tip of the magnetic needle of a dip circle placed in the plane of magnetic meridian points above the horizontal. The horizontal component of the earth’s field is measured to be Specify the direction and magnitude of the earth’s field at the location.At a certain location in Africa, a compass points west of the geographic north. The north tip of the magnetic needle of a dip circle placed in the plane of magnetic meridian points above the horizontal. The horizontal component of the earth’s field is measured to be Specify the direction and magnitude of the earth’s field at the location.

Ans: In the above question it is given that: Angle of declination, $\theta=12^{\circ}$ Angle of dip, $\delta=60^{\circ}$ Horizontal component of earth's magnetic field, $B_{H}=0.16 \mathrm{G}$...

### Two long and parallel straight wires and carrying currents of and in the same direction are separated by a distance of . Estimate the force on a section of wire A.

Ans: We are given the following: Current flowing in wire $A_{1} I_{A}=8.0 \mathrm{~A}$ Current flowing in wire $B, I_{B}=5.0 \mathrm{~A}$ Distance between the two wires, $r=4.0 \mathrm{~cm}=0.04...

### A wire carrying a current of is placed inside a solenoid perpendicular to its axis. The magnetic field inside the solenoid is given to be . What is the magnetic force on the wire?

Ans: We are given the following: Length of the wire, $I=3 \mathrm{~cm}=0.03 \mathrm{~m}$ Current flowing in the wire, $1=10 \mathrm{~A}$. Magnetic field, $B=0.27 \mathrm{~T}$ Angle between the...

### What is the magnitude of magnetic force per unit length on a wire carrying a current of and making an angle of with the direction of a uniform magnetic field of

Ans: We are given the following: Current in the wire, $I=8 \mathrm{~A}$ Magnitude of the uniform magnetic field, $B=0.15 \mathrm{~T}$ Angle between the wire and magnetic field, $\theta=30^{\circ}$...

### A long straight wire carries a current of . What is the magnitude of the field at a point from the wire?

Ans: We are given the following: Current in the wire, $\mathrm{I}=35 \mathrm{~A}$ Distance of a point from the wire, $r=20 \mathrm{~cm}=0.2 \mathrm{~m}$ Magnitude of the magnetic field at this point...

### State Biot-Savarts law. Derive an expression for magnetic field at the center of a circular coil of -turns carrying current .

Ans: Biot - Savart law states that the magnetic field $\mathrm{dB}$ due to a current element dI at any point would be as following: $$ \begin{array}{l} \mathrm{dB} \propto \mathrm{dl} \\ \mathrm{dB}...

### 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.

### Two heated wires of the same dimensions are first connected in series and then it’s parallel to a source of supply. What will be the ratio of heat produced in the two cases?

Ans: It is known that, $$ \begin{array}{l} H=I^{2} R t \quad\left(I=\frac{V}{R}\right) \\ \Rightarrow H=\frac{V^{2}}{R^{2}} \times R \times t \\ \Rightarrow H=\frac{V^{2}}{R} t \\ \Rightarrow H...

### Resistivities of copper, silver and manganin are and respectively which of these is the best conductor?

Ans: The resistance is directly proportional to specific resistance (resistivity), when length and area of cross-section is made constant. $R=\frac{\rho I}{A}$ Hence, silver is the best conductor as...

### 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...

### State Gauss’s Theorem in electrostatics? Using this theorem define an expression for the field intensity due to an infinite plane sheet of change of charge density .

Ans: Gauss's Theorem has a statement that electric flux through a closed surface enclosing a charge $q$ in vacuum is $\frac{1}{\epsilon_{0}}$ times the magnitude of the charge enclosed $\mathrm{is}...

### Prove that the energy stored in a parallel plate capacitor is given by

Ans: Let us suppose a capacitor is connected to a battery and it supplies a small amount of change dq at constant potential $V$, then a small amount of work done by the battery is given by $$...

### Two dielectric slabs of dielectric constant and are filled in between the two plates, each of area A of the parallel plate capacitor as shown in the figure. Find the net capacitance of the capacitor? Area of each plate

Ans: In the question, the two capacitors are in parallel Net Capacitance, $C=C_{1}+C_{2}$ $$ \begin{array}{l} \mathrm{C}_{1}=\frac{\mathrm{K}_{1}...

### Describe schematically the equipotential surfaces corresponding to a) a constant electric field in the z-direction,

Ans: Equidistant planes which are parallel to the $x-y$ plane are the equipotential surfaces. b) a field that uniformly increases in magnitude but remains in a constant (say, z) direction, Ans:...

### In a Van de Graaff type generator a spherical metal shell is to be a electrode. The dielectric strength of the gas surrounding the electrode is . What is the minimum radius of the spherical shell required? (You will learn from this exercise why one cannot build an electrostatic generator using a very small shell which requires a small charge to acquire a high potential.)

Ans: Given that, Potential difference is given as, $V=15 \times 10^{6} \mathrm{~V}$ Dielectric strength of the surrounding gas $=5 \times 10^{\top} \mathrm{Vm}^{-1}$ Electric field intensity is...

### Two charges and are placed at points and apart. a) Identify an equipotential surface of the system.

Ans: The situation is represented in the adjoining figure. An equipotential surface is the plane on which the total potential is zero everywhere. This plane is normal to line AB. The plane is...

### The distance between the plates of a parallel plate capacitor is d. A metal plate of thickness is placed between the plates. What will be the effect on the capacitance?

Ans: For air $C_{0}=\frac{A \in_{0}}{d}$ Thickness $t=\frac{d}{2}$ only when $k=\infty$ $$ \begin{array}{l} C_{0}=\frac{A \in_{0}}{d} \\ C_{\text {mat }}=\frac{A \in_{0}}{(d-t)} \end{array} $$ $$...

### 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 $\mathrm{~ ( 2 c ) r o m}$

### A parallel plate capacitor with air between the plates has a capacitance of 8pF . What will be the capacitance if the distance between the plates is reduced by half and the space between them is filled with a substance of dielectric constant 6 ?

Ans: For air, capacitance can be expressed as, $C_{0}=\frac{A \in_{0}}{d}$ $$ C_{0}=8 \times p F=8 \times 10^{-12} F $$ Now $d^{\prime}=\frac{d}{2}$ and $K=6$ $$ \begin{array}{l} \Rightarrow...

### Show mathematically that the potential at a point on the equatorial line of an electric dipole is Zero?

Ans: Electric potential at point on the equatorial line of an electric dipole can be expressed mathematically as: $$ \begin{array}{l} V=V_{P A}+V_{P B} \\ \Rightarrow...

### 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...

### Electric charge is uniformly distributed on the surface of a spherical balloon. Show how electric intensity and electric potential vary

a) on the surface Ans: Electric field intensity on the surface of the balloon would be, $$ E=\frac{\sigma}{\varepsilon_{0}} $$ Electric potential on the surface of the balloon would be, $$ V=\frac{K...

### A sphere of radius encloses a charge If there is another concentric sphere of radius and there is no additional change between and , then find the ratio of electric flux through and .

Ans: We may recall that the expression for electric flux through a surface enclosing charge q by Gauss's law is given by, $$ \phi=\frac{q}{E_{0}} $$ Where, $\varepsilon_{0}$ is the permittivity of...

### A sphere of radius encloses a charge If there is another concentric sphere of radius and there is no additional change between and , then find the ratio of electric flux through and .

Ans: We may recall that the expression for electric flux through a surface enclosing charge q by Gauss's law is given by, $$ \phi=\frac{q}{E_{0}} $$ Where, $\varepsilon_{0}$ is the permittivity of...

### Two charges and are separated by a distance of . Find the point on the line joining the two charges where electric field is zero.

Ans: Let $p$ be the point (at $x$ distance from charge $+q$ ) on the line joining the given two charges where the electric field is zero. We know that the electric field at a point at r distance...

### A particle of mass and charge a is released from rest in a uniform electric field of intensity E. Calculate the kinetic energy attained by this particle after moving a distance between the plates.

Ans: We have the electrostatic force on a charge a in electric field E given by. $\mathrm{F}=\mathrm{q} \mathrm{E} \quad \ldots \ldots(1)$ Also, we have Newton's second law of motion given by, $$...

### 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...

### Explain the meaning of the statement ‘electric charge of a body is quantized”.

Ans: The statement 'electric charge of a body is quantized' suggests that only integral $(1,2,3,4, \ldots, \mathrm{n})$ number of electrons can be transferred from one body to another. This further...

### 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...

### The graph shows the variation of voltage across the plates of two capacitors and versus increase of charge stored on them. Which of the two capacitors have higher capacitance? Give reason for your answer.

Ans: It is known that $c=\frac{Q}{V}$ Clearly, for a given charge $\mathrm{Q}$. $c \propto \frac{1}{V}$ Now, from the given graph, it is seen that $\mathrm{V}_{\mathrm{A}}

### No two electric lines of force can intersect each other. Why?

Ans: Two electric lines of force can never intersect each other. Suppose if they intersect, then at the point of intersection, there can be two tangents drawn. These two tangents are supposed to...

### A free proton and a free electron are placed in a uniform field. Which of the two experiences greater force and greater acceleration?

Ans: Force on both the electron as well as the proton in the uniform field would be equal because $\mathrm{F}=\mathrm{kq}$ and it is known that charge on both electron and proton are the same. On...

### Define one coulomb.

Ans: Charge on a body is said to be 1 coulomb if it experiences a force of repulsion or attraction of $9 \times 10^{9} \mathrm{~N}$ from another equal charge when they are separated by a distance of...

### Which physical quantity has its S.I. unit

1. ?

2. ?

Ans: 1.The S.I. unit of electric dipole moment is $\mathrm{Cm}$. 2. The S.I. unit of electric field intensity is N/C.

### A charged rod P attracts a rod R whereas P repels another charged rod Q. What type of force is developed between and ?

Ans: Suppose that the rod $\mathrm{P}$ is negatively charged. As it attracts rod $\mathrm{R}$, it can be said that $\mathrm{R}$ is positively charged. Also, since $P$ repels rod $Q$, it can be said...

### Does the force between two point charges change if the dielectric constant of the medium in which they are kept is increased?

Ans: Dielectric constant of a medium is given by $$ \begin{array}{l} k=\frac{F_{y}}{F_{M}}=\frac{\text { force between the charges in vaccum }}{\text { force between two charges in medium }} \\...

### Unit of electric potential is i) joule/coulomb ii) joule-coulomb iii) volt/metre iv) joule/coulomb-metre.

Correct option is (i)

### Distinguish between electric potential and electric potential energy.

Electric potential at a place in an electric field is the amount of effort done to bring the unit positive charge from infinity to that point, whereas electric potential energy is the energy...

### The ratio of electric force between two electrons to two protons separated by the same distance in the air is: A B C D None of these

Correct option is (A) $10^{\circ}$ $\frac{\mathrm{F}_{\mathrm{e}}}{\mathrm{F}_{\mathrm{p}}}=10^{0}=1$, because force depends only on charges, distance and nature of medium and not type of charge. As...

### Two particles each of mass and carrying charge are separated by some distance. If they are in equilibrium under mutual gravitational and electrostatic forces, then (in ) is of the order of:

A

B

(C)

D

Correct option is (B) $10^{-10}$ Given : Gravitational force $=$ Electrostatics force Let the distance between the rwo charges be r. $$ \begin{array}{l} \Rightarrow \frac{\mathrm{G}(\mathrm{m})...

### Electrostatic force and gravitational force differ in which respect?

In electrostatic force, the force of medium depends on charges while the force of the medium due to gravity does not depend on masses. There is no concept of induced mass.

### Electrostatic force and gravitational force differ in which respect?

A Conservative force,

B Central force

c Principle of superposition

D Dependence on the intervening medium

Correct option is (D) Dependence on the intervening medium In electrostatic force, the force of the medium depends on charges while the force of the medium due to gravity does not depend on masses....

### The excess (equal in number) number of electrons that must be placed on each of the two small spheres spaced 3cm apart with a force of repulsion between them to be is :

A 25

B 225

C 625

D 1250

Correct option is (C) 625 We need force of repulsion $=10^{-19} \mathrm{~N}$ Let $n$ no. of increase electrons be placed on each sphere $$ \begin{array}{l} \Rightarrow...

### In comparison to the electrostatic force between two electrons, the electrostatic force between two protons is : A zero B smaller c same D greater

Correct option is(c) same Since the magnitude of the charge of electron and proton is the same, e, the electrostatic force between two protons is the same compared to the electrostatic force between...

### In an A.C. circuit having resistance and capacitance :

A emf leads ahead of the current

B current lags behind the emf

c both the current and emf are in phase

D current leads ahead of the emf

Correct option is D current leads ahead of the emf $\mathrm{D}$ In circuits with primary capacitive loads, currently leads to the voltage. This is because the current must flow first to the two...

### A parallel-plate air condenser of plate area A and separation d is charged to potential V and then the battery is removed. Now a slab of dielectric constant k is introduced between the plates. If Q, E, and W denote respectively the magnitude of the charge on each plate, the electric field between the plates (after the introduction of the dielectric slab) and work done on the system in the process of introducing the slab, then

A

B

c

Correct option is A $\mathrm{W}=\frac{\varepsilon_{0} \mathrm{~A} \mathrm{~V} \mathrm{~h}^{2}}{2 \mathrm{~d}}(1-1 / \mathrm{k})$ C $Q=\frac{\varepsilon_{0} A V}{d}$ D $\quad E=\frac{V}{k d}$ As...

### A parallel plate capacitor with a dielectric slab of dielectric constant 3, filling the space between the plates, is charged to a potential V. The battery is then disconnected and the dielectric slab is withdrawn. It is then replaced by another dielectric slab of dielectric constant 2. If the energies stored in the capacitor before and after the dielectric slab is changed are and , then is:

A

B

c

D

Correct option is B $\frac{2}{3}$ Let the charge stored by a capacitor with dielectric constant 3 be $Q$. Thus energy stored be $\frac{\mathrm{Q}^{2}}{2 \mathrm{C}_{1}}$ Since the charge remains the...

### A parallel plate capacitor is first charged and then isolated, and a dielectric slab is introduced between the plates. The quantity that remains unchanged is:

A charge Q

B potential V

C capacity C

D energy U

The correct option is (A) charge Q When the capacitor is kept at a voltage, it gains charge. Now when the system is isolated, the charge present on the capacitor cannot change because of the law of...

### When a dielectric slab is introduced between the two plates of the condenser then it’s capacity

A remains constant

B increases

C decreases

D may increase or decrease depending on the material of the dielectric slab

$\mathrm{~ O ~ W e i s c o d i s ~ T o p}$ Correct option is B increases As the dielectric slab is introduced there is some charge distribution in the slab and because of this, the electric field...

### In the LCR circuit if resistance increases, then the quality factor

A) increases finitely

B decreases finitely

C remains constant

D None of these

The correct option is B decreases finitely Quality factor $Q$ is given by: $$ \mathrm{Q}=\frac{\omega_{0} \mathrm{~L}}{\mathrm{R}} $$ Thus, as $\mathrm{R}$ increases Q definitely decreases.

### The magnitude of force between two plates of a capacitor is Transformer works on.

A

B DC only

C Both and DC

D AC more effectively than DC

The correct option is A AC only Transformer works on the principle of Electromagnetic induction i.e an emf is induced in the coil if the magnetic flux linked with the coil changes. Magnetic flux in...

### Force between two plates of a capacitor is :

A

B

C

D none of these

Correct option is B $\frac{\mathrm{Q}^{2}}{2 \mathrm{\varepsilon}_{0} \mathrm{~A}}$ The magnitude of electric field by any one plate is $\mathrm{E}=\frac{\sigma}{2...

### Quality factor of series resonance circuit is given by

A

B

c)

D

Correct option is D $\frac{\mathrm{f}_{0}}{\mathrm{f}_{2}-\mathrm{f}_{1}}$ Quality factor is a relation between stored energy and energy dissipation in a device or system. As per definition of...

### What is Q-factor? Write its expression and write the conditions for its maximum value.

Q-factor: In LCR Circuit, the ratio of resonance frequency to the difference of its neighboring frequencies so that their corresponding current is $1 / \sqrt{2}$ times of the peak value, is called...

### Using Biot-Savart’s law, obtain an expression for the magnetic field at a distance r meter from an infinitely long wire carrying a current of i ampere.

Biot savart law is the base of all magnetism and the effects of current. It states that the magnetic field intensity due to an element of a current-carrying wire at a point near the element is...

### The principle on which transformer works is?

A Mutual induction

B Self induction

C Electromagnetic induction

D None of these

The correct option is A Mutual induction Mutual inductance is where the magnetic field generated by a coil of wire induces a voltage in an adjacent coil of wire. A transformer is a device...

### A transformer is

A) A device for stepping up D.C.

B )A generator of current

C) Device for converting direct current into alternating current

D) A device for stepping up or down the voltage of . supply

The correct option is D) A device for stepping up or down the voltage of $A C$. supply A transformer is a device that is used to either raise or lower voltages and currents in an electrical circuit....

### Explain the construction of the transformer.

For the construction of the transformer, you must have two coils having mutual inductance and a laminated steel core. The two coils are insulated from each other and from the steel core. The device...

### Write the principle and explain the construction and working of a transformer. Define its efficiency.

Principle: The transformer is based on the principle of electromagnetic induction. The phenomenon of producing an induced emf due to the changes in the magnetic flux associated with a closed circuit...

### The phase difference between the applied emf and the line current in an anti-resonant circuit at resonance is

A radian

B radian

c radian

D zero

The correct option is D zero We know that phase difference is given by: $$ \phi=\arctan \left(\frac{\left(\mathrm{X}_{\mathrm{L}}-\mathrm{X}_{\mathrm{C}}\right)}{\mathrm{R}}\right) $$ at resonance...

### The frequency at which the impedance of the circuit boorens mavimum is

a

b

c

D

Correct option is c $\frac{1}{2 \pi} \sqrt{\frac{1}{L C}-\frac{R^{2}}{L^{2}}}$ Megritude of admittanos $Y=\frac{1}{Z}$ is given by: $$ |\mathrm{Y}|=\frac{\mid \mathrm{H}^{2}...

### The resonent froquengy in an anti resonant circuitis:

a

b

c

D

Correct option is a $\frac{1}{2 \pi \sqrt{L C}}$ For rescnance $$ \mathrm{X}_{\mathrm{L}}=\mathrm{X}_{\mathrm{E}} $$ $$ \begin{aligned} \mathrm{kL} &=\frac{1}{\mathrm{wC}} \\ \mathrm{w}...

### The study of the earth’s magnetic field is called

A Terrestrial Magnetism

B Magneto Therapy

C Special Magnetism

D None of these

The correct option is A Terrestrial Magnetism

### Power consumed in an AC circuit becomes zero if

A Inductance and resistance are both high.

B inductance and resistance are both low.

C inductance is very high and resistance is negligible.

D inductance is low and resistance is high.

The correct option is C inductance is very high and resistance is negligible. The power consumption in an AC circuit is zero when the circuit contains only inductance or capacitance since the...

### The terminal potential difference of a cell is equal to the emf of the cell when:

The terminal potential difference of a cell is equal to the emf of the cell when: → The cell is an open circuit. → The internal resistance of the cell is zero. → The load resistance much greater...

### What do you understand by angle of dip?

The angle of dip is the angle between the direction of the earth's magnetic field and the plane of the horizon

### State true and false, mass is not conserved during a chemical reaction.

True

False

The correct option is False In a chemical reaction, the total mass of the reactants is equal to the total mass of the product hence the mass remains conserved in a chemical reaction.

### A circular coil a carrying current produces a magnetic field at its centre. This coil is made itself to 10 turns and the same current is set up in it. The magnetic field at its centre would be

A

B

C

D

Correct option is B $\mathrm{B}=10 \mathrm{~B}_{0}$ Electric current in a circular loop creates a magnetic field which is more concentrated in the center of the loop than outside the loop....

### An electric current i is flowing in a circular coil of radius a. At what distance from the center of the axis of the coil will the magnetic field be of its value at the centre?

A

в

c

D

Correct option is B $\sqrt{3} \mathrm{a}$ Magnetic field due to the circular current (I) carrying coil of radius $\mathrm{a}$, at a distance $r$ from the center of the coil is given by: $$...

### (a) Determine the value of phase difference between the current and the voltage in the given series LCR circuit. (b) Calculate the value of the additional capacitor which may be joined suitably to the capacitor C that would make the power factor of the circuit unity

(a)The phase difference between current and voltage $\phi$ is given by $$ \begin{array}{l} \tan \phi=\frac{\mathrm{X}_{\mathrm{C}}-\mathrm{X}_{\mathrm{L}}}{\mathrm{R}} \\...

### An ammeter of resistance and range is to be used to read potential difference upto 1 volt. It will have to be connected to A resistance in series B resistance in parallel C resistance in parallel D resistance in series

Correct option is A $99.8 \Omega$ resistance in series $$ \begin{array}{l} \mathrm{V}=\mathrm{I}_{g}\left(\mathrm{R}+\mathrm{R}_{g}\right) \\ \therefore 1=10 \times 10^{-3} \times(\mathrm{R}+0.2) \\...

### A circular current carrying coil has a radius r. Find the distance from the centre of coil, on its axis, where the magnetic induction will be 1/8 th of its value at the centre of coil.

$$ \begin{array}{l} B_{A}=\frac{\mu_{1} I}{2} \times \frac{r^{2}}{\left(x^{2}+r^{2}\right) \frac{3}{2}}\\ \mathrm{B}_{0}=\frac{\mu_{1} \mathrm{I}}{2} \times \frac{\mathrm{r}^{2}}{\mathrm{r}^{3}}\\...

### Explain the term ‘drift velocity’ of electrons in a conductor. Hence obtain the expression for the current through a conductor in terms of ‘drift velocity’.

The average velocity of all the free electrons in the conductor is called the drift velocity of free electrons of the conductor. When a conductor is connected to a source of emf an electric field is...

### Given below are some fomous numbers associated with electromagnetic radiation in different contexts in physics .State the part of the electromagnetic spectrum to which each belongs . 21 cm (wavelength emitted by atomic hydrogen in interstellar space ).

Radiation of wavelength of 21 cm : It corresponding to radio waves of short wavelength.

### The resistance required to be connected in parallel to an ammeter in order to increase its range 10 times, will be

A one-tenth the resistance of ammeter

B nine times the resistance of ammeter

C ten times the resistance of ammeter

D one-ninth the resistance of ammeter

Correct option is D one-ninth the resistance of ammeter Full scale deflection voltage be V Now initiall range is I $$ \mathrm{V}=\mathrm{IR} $$ Now, Range is made $10 \mathrm{I}$ $$ \begin{array}{l}...

### Which part of the electromagnetic spectrum is used in operating a RADAR?

Microwaves are used in operating a RADAR.

### Which part of electromagnetic spectrum does the wavelength correspond to?

$\mathrm{X}$-rays part of electromagnetic spectrum does the wavelength $10^{-10} \mathrm{~m}$ correspond to.

### In the order of increasing frequency, the electromagnetic spectrum may be arranged as

A Gamma rays, -rays, visible light, radio waves

B -rays gamma rays, visible light, radio waves

C Radio waves, visible light, -rays, gamma rays

D Radio waves, visible light, gamma rays, -rays

Correct option is C Radio waves, visible light, $\mathrm{X}$-rays, gamma rays The electromagnetic spectrum is a continuum of all electromagnetic waves arranged according to frequency and wavelength....

### Find the expression of magnetic, field produced at the centre of current carrying circular coil.

Consider a circular coil of radius a and carrying current I in the direction shown in Figure. Suppose the loop lies in the plane of paper. It is desired to find the magnetic field at the centre...

### The magnetic field in a plane electromagnetic wave is given by

Find the maximum electric field and the average energy density corresponding to the electric field.

Given: The magnetic field in a plane electromagnetic wave is given by $$ \mathrm{B}=(200 \mu \mathrm{T}) \sin \left[\left(4.0 \times 10^{1} 5_{\mathrm{s}}^{-1}\right)(\mathrm{t}-\mathrm{x} /...

### Use Gauss’s theorem to find the electric field due to a uniformly charged infinitely large plane thin sheet with surface charge density

Consider an infinite plane which carries the uniform charge per unit area $\sigma$ Let the plane coincides with the $y-z$ plane. Let us draw a cylindrical gaussian surface, whose axis is normal to...

### Derive an expression for electric potential at a point due to an electric dipole. Discuss the special cases.

Let an electric dipole consist of two equal and opposite point charges $-\mathrm{q}$ at $A$ and $+\mathrm{q}$ at $\mathrm{B}$,separated by a small distance $\mathrm{AB}=2 \mathrm{a}$, with centre at...

### Two charges and are located apart. At what point on the line joining the two charges is the electric potential zero? Take the potential at infinity to be zero.

Let $\mathrm{p}$ be the point of zero potential be $\mathrm{p}$ at distance $\mathrm{r}$ from the charge $1 .$ $\mathrm{d}=16 \mathrm{~cm}$ Electric potential, $\mathrm{v}=\mathrm{q}_{1} / 4 \pi...

### An electric dipole has the magnitude of its charge as q and its dipole moment is p. It is placed in uniform electric field E. If its dipole moment is along the direction of the field, the force on it and its potential energy are respectively

A q.E and max

B and .

C q.E and

D zero and min.

Correct option is D zero and min. When the dipole is in the direction of field then net force is $\mathrm{q} \mathrm{E}+(-\mathrm{q} \mathrm{E})=0$ and its potential energy is minimum $=-$ p.E...

### What is the angle between the electric dipole moment and the electric field due to it on the axial line?

A

VB

C

D none of these

Correct option is A $0^{\circ}$ Electric field $\overrightarrow{\mathrm{E}}$ is along the dipole axis $\therefore \theta=0^{\circ}$

### Why do magnetic field lines not intersect each other?

If magnetic field lines cross, there will be two directions of the same field at the crossing point, which is not conceivable. As a result, the field lines do not cross or intersect

### Explain the working of P-N junction diode in forward and reverse biased mode

When the positive terminal of a cell or battery is connected to the p-side of the junction and the negative terminal to the n side, the diode is said to be forward biassed. The depletion region...

### State Bohr’s Model.

The Bohr Atomic Model's Postulates Electrons orbit the nucleus in a predetermined circular path known as "orbits," "shells," or "energy levels." Each circular orbit has a given quantity of energy,...

### 1) The Bohr atomic model hypothesis made correct predictions for lower sized atoms like hydrogen, but poor spectrum predictions were achieved when larger atoms were taken into account. 2) When the spectral line is split into numerous components in the presence of a magnetic field, it fails to explain the Zeeman phenomenon.

1) The Bohr atomic model hypothesis made correct predictions for lower sized atoms like hydrogen, but poor spectrum predictions were achieved when larger atoms were taken into account. 2) When the...

### What is displacement current?

Current passes through the circuit while a capacitor is charging (or draining). However, no actual charge transfer occurs in the insulated region between the capacitors, which is incompatible with...

### List the properties of electromagnetic waves

The oscillating electric and magnetic fields at right angles to one other make up electromagnetic waves. Properties Electric fields and magnetic fields oscillate at right angles to one other to...

### What is displacement current? Obtain an expression of displacement current for a charged capacitor. Write Ampere-Maxwell’s law.

Current passes through the circuit while a capacitor is charging (or draining). However, no actual charge transfer occurs in the insulated region between the capacitors, which is incompatible with...

### The electromagnetic waves travel in free space with the velocity of

A Sound

B Light

c Greater than that of light

D Greater than that of sound

Correct option is B Light Electromagnetic waves travel in free space or vacuum with the velocity of light, $\mathrm{c}=3 \times 10^{8} \mathrm{~m} / \mathrm{s}$

### What is the wavelength of the wave whose frequency is ?

A

B

C ,

D

Correct option is A $0.3$ $$ \mathrm{C}=\mathrm{v} \lambda $$ $$ \lambda=\frac{\mathrm{c}}{\mathrm{v}}=\frac{3 \times 10^{8}}{10^{12}} $$ $$ \begin{array}{l} =3 \times 10^{-4} \mathrm{~m} \\ =0.3...

### If the instantaneous magnetic flux and induced emf produced in a coil is and respectively, then according to Faraday’s law of electro magnetic induction:

A E must be zero if and changing

B if

C if is changing.

D then must be zero

Correct option is c $E \neq 0$ if $\phi$ is changing. Farady's law states that time varying magnetic flux can induce an e.m.f. $\mathrm{E}=$ Electric field, Induced $$ \mathrm{E}=-\frac{\mathrm{d}...

### How electromagnetic waves are produced

Moving charges produce electromagnetic waves, which are a mix of electric and magnetic field waves. A charged particle is the starting point for all electromagnetic waves. An electric field is...

### Write Faraday’s laws of electro magnetic induction.

There are two Faraday's laws of Electromagnetic induction, 1) First Law: Whenever magnetic flux linked with the circuit changes, an emf is induced in it. 2)Second Law: The magnitude of emf is...

### If the instantaneous magnetic flux and induced emf produced in a coil is and respectively, then according to Faraday’s law of electro magnetic induction:

A E must be zero if and changing

B if

c if is changing.

D then must be zero

Correct option is c $E \neq 0$ if $\phi$ is changing. Farady's law states that time varying magnetic flux can induce an e.m.f. $\mathrm{E}=$ Electric field, Induced $$ \mathrm{E}=-\frac{\mathrm{d}...

### The induced emf produced when a magnet is inserted into a coil does not depend upon:

A The number of turns in the coil

B The resistance of the coil

C The speed of approach of the magnet

D All the above

Correct option is B The resistance of the coil The induced emf produced when a magnet is inserted into a coil does not depend upon the resistance of the coil.

### When current changes from to in in an inductor the induced emf is found to be , then find the value of self-inductance is :

A

B

C

D

Correct option is C $2.5 \mathrm{H}$ $$ \begin{array}{l} \Delta \mathrm{I}=(4-0)=4 \mathrm{~A} \\ \mathrm{t}=0.1 \mathrm{~s} \\ \mathrm{e}=100 \mathrm{~V} \\...

### State whether true or false : Soft iron is used in electromagnets because soft iron does not retain magnetism permanently.

A True

B False

Correct option is A True Soft iron core is used in electromagnets because soft iron does not retain magnetism permanently, that is, it loses the magnetism as soon as magnetic field is removed. Hence...

### The unit of inductance is

A Volt /Ampere

B Joule/ampere

C Volt-sec/ampere

D Volt-ampere

Correct option is (C) Volt-sec/ampere $$ \begin{aligned} e &=L \frac{d i}{d t} \\ \Rightarrow & L=\frac{V \text { olt }-\text { sec }}{\text { Ampere }} \end{aligned} $$

### Consider the following statements :

(i) Soft iron conducts electricity

(ii) Soft iron is magnetic material

(iii) Soft iron is used for magnetic permanent magnets

(iv) Soft iron is used as electro magnet

A (i) and (ii) are correct

B (i) and (iii) are correct

C (ii) and (iv) are correct

D (i), (ii) and (iv) are correct

Correct option is D (i), (ii) and (iv) are correct Soft iron conducts electricity It is a magnetic material It is not used for magnetic permanent magnets It is used as electro magnet

### Alnico is used for making permanent magnets because it has

A High coercivity and high retentivity

B high coercivity and low retentivity

C low coercivity and low retentivity

D low coercivity and high retentivity

The correct option is A High coercivity and high retentivity Since of its high coercivity and low retentivity, Alnico is used to make permanent magnets because it can be quickly magnetised in an...

### For making an electro-magnet, substance should be of

i) high retentivity and high coercivity

ii) low retentivity and high cocrcivity

iii) high retentivity and low coercivity

iv) low retentivity and low coercivity

CORRECT OPTION IS iii) high retentivity and low coercivity The capacity of a substance to remain magnetised after the external magnetising field has vanished is known as retentivity. A material with...

### Electrical resistivity of a given metallic wire depends upon:

A its length

B its thickness

C its shape

D nature of the material

Correct option is D nature of the material Hint: Resistivity is an intrinsic property of a metal. Step 1: Explanation of Resistivity Resistivity of a metallic wire does not depend on its geometry...

### The resistivity of a wire depends on its

A length

B area of cross-section

c material

D all of the above three factors

Correct option is (C) material The resistivity or specific resistance of a material is an intensive property (property which does not depend on the system size or the amount of material in the...

### What are the factors on which resistance of a conductor depends

Resistance can be defined as $$ \begin{array}{l} \mathrm{R} \propto \frac{1}{\mathrm{~A}} \\ \Rightarrow \mathrm{R}=\rho \frac{1}{\mathrm{~A}} \end{array} $$ where $\rho=$ specific resistance or...

### The product of resistivity and specific conductivity of a cylindrical conductor depends on

i) temperature

ii) material

iii) area of cross-section

iv) none of these

Correct option is (iv) None of the above The product of resistivity and conductivity of a cylindrical conductor is constant The product becomes $\rho \times \sigma$, where pis resistivity and...

### An infinite plane sheet of charge in vacuum has a uniform surface charge density . The electric field intensity near it is

A

B

C

D

Correct option is A $\frac{\sigma}{\varepsilon_{0}}$ Charge density $=\sigma$ Electric field intensity near it is - Using gauss law, $\lambda=\frac{\sigma}{\varepsilon_{0}}$

### Which of the following is not a unit of electric field intensity?

A

B

c

D None of these

Correct option is D None of these $$ \begin{array}{l} \mathrm{F}=\mathrm{q} \mathrm{E} \\ \mathrm{E}=\frac{\mathrm{F}}{\mathrm{q}}=\frac{\mathrm{N}}{\text { Coulomb }}=\mathrm{NC}^{-1}=\text { SI...

### A current i ampere flows along an infinitely long straight thin walled tube, then the magnetic induction at any point inside the tube is

A infinite

B zero

C tesla

D tesla

Correct option is B zero Using ampers law, there is no current enclosed in the pipe $\int \overline{\mathrm{B}} \cdot \overline{\mathrm{dl}}=\mu_{0}$ Ienclosed

### A current i amp flows along an infinitely long straight thin conductor. Then the magnetic induction at any point on the axis of the conductor is

A infinity

B zero

C

D

Correct option is B zero $\operatorname{Sin} \theta=0$ on any pt, on the axis of conductor carrying current $$ \mathrm{B}=\frac{\mu_{0}}{4 \Pi} \mathrm{i} \frac{\mathrm{d}] \operatorname{Sin}...

### Two thin, long, parallel wires, separated by a distance ‘ ‘ carry a current of ‘ ‘ in the same direction. They will

A repel each other with a force of

B attract each other with a force of

C repel each other with a force of

D attract each other with a force of

Correct option is B attract each other with a force of $y_{0} i^{2} /(2 \pi \mathrm{d})$ $$ \frac{\mathrm{F}}{\mathrm{l}}=\frac{\mu_{0} \mathrm{i}_{1} \mathrm{i}_{2}}{2 \pi \mathrm{d}} $$ $$...

### Two very long straight parallel wires carry steady currents i and in opposite directions. The distance between the wires is . at a certain instant of time, a point charge is at a point equidistant from the two wires in the plane of the wires. Its instantaneous velocity is perpendicular to this plane. The magnitude of the force, due to the magnetic field acting on the charge at this instant is:

A

B

C

D zero

Correct option is (D) zero Magnetic field at P is perpendicu;ar to paper inward due to both the wires. Charged particle is also projected in the same direction. So, force on the charged particle is...

### A charge is moving with a velocity v parallel to a magnetic field . Force on the charge due to magnetic field is

A quB

B

C zero

D

Correct option is C zero $$ \begin{array}{l} \mathrm{F}_{\mathrm{n}}=\mathrm{q}(\overrightarrow{\mathrm{v}} \times \overrightarrow{\mathrm{B}}) \\ =\mathrm{qvB} \sin \theta \\ =0 \text { (because }...

### The force acting on charge moving with velocity perpendicular to magnetic field is

i)

ii)

iii)

iv)

Correct option is (I) $F=q v B$ Magnetic force $\mathrm{F}=\mathrm{q}(\mathrm{v} \times \mathrm{B})=\mathrm{qvB} \sin \theta$ where $\theta$ is the angle between $v$ and $B$. Given:...

### The length of a metallic wire of resistance is stretched two times its initial length. Its new resistance is

i)

ii)

iii)

iv)

Correct option is (iv) $200 \Omega$ Resistance of wire $\mathrm{R}=\rho \frac{\mathrm{L}}{\mathrm{A}}=\rho \frac{\mathrm{L}^{2}}{\mathrm{AL}}=\rho \frac{\mathrm{L}^{2}}{\mathrm{~V}}$...

### The unit of electric field intensity is

i) newton/metre

ii) coulomb/newton

iii) newton/coulomb

iv) joule/newton

iii) newton/coulomb The amount of force experienced by a unit charged particle when it is placed in the electric field is known as Electric field intensity. The S.I unit of electric field intensity...

### A Carnot engine, having an efficiency of as heat engine, is used as a. refrigerator. If the work done on the system is , the amount of energy absorbed from the reservoir at lower temperature is:

A

B

c

D

Correct option is A $90 \mathrm{~J}$ efficiency of carnot cycle is given as $$ \eta=\frac{W}{Q_{H}} $$ where $W$ is work done and $Q_{H}$ is amount of heat added to system. $$ \begin{array}{l}...

### Two identical sonometer wires have a fundamental frequency of , when kept under the same tension. What fractional increase in the tension of one wire would cause an occurrence of 5 beats , when both wires vibrate together?

A 2

B 3

C 4

D 5

Solution (A) 2 $\mathrm{n} \propto \mathrm{V}$ and $\mathrm{V} \propto \sqrt{T}$ $$ \Rightarrow \mathrm{n} \propto \sqrt{\mathrm{T}} . .(1) $$ 5 beats/sec are obtained when the frequency of one...

### The amplitude, frequency and velocity of the component waves producing a stationary wave are and second respectively. Write the equation of stationary wave

Since the waVe equation of a travelling wave:- $y=a \sin 2 \pi(t / T-x / \pi)$ $\mathrm{a}=$ Amplitude $t=$ time $\mathrm{T}=$ Time Period $x=$ Path difference $\pi=$ wavelength Let...

### The equation of simple harmonic wave is given by , where and are in and is in seconds . The phase difference between two particles apart at any instant is

A

B

C

D

Correct option is D $72^{\circ}$ Given equation can be written as $y=6 \sin (4 \pi t-0.2 \pi x)$ $\therefore$ Phase $\phi=-0.2 \pi x$ $\Rightarrow \phi_{1}=-0.2 \pi \mathrm{x}_{1}$ and...

### Derive expression for the ratio of specific heats if the gas has degrees of freedom.

$\mathrm{~ O ~ W e i r i s o s t y ~ T o p p r}$ The molar specific heats of a gas having $\mathrm{f}$ degrees of freedom is given by : $$ \mathrm{C}_{\mathrm{r}}=\frac{1}{2} \mathrm{f} \mathrm{R}...

### At what temperature the average translational of the molecules of a gas will become equal to the of an electron accelerated from rest through potential difference?

A

B

c

D none of these

Correct option is C $7.73 \times 10^{3} \mathrm{~K}$ $$ \frac{3}{2} \mathrm{KT}=1 \mathrm{eV}=1.6 \times 10^{-19} \mathrm{~J} $$ Or" $$ \mathrm{T}=\frac{2 \times 1.6 \times 10^{-19}}{3 \times 1.38...

### What is surface energy? Establish the relation between surface tension and surface energy

$S=$ surface tension of soap Liquid $1=$ length of $\mathrm{PQ}$ Total Inward Force on the wire P Q $$ F=S \times 21 $$ To increase surface area we have to pull wire $\mathrm{P} \mathrm{Q}$ outwards...

### The elastic energy stored per unit volume in a stretched wire is

A

B ,br>C

D

Correct option is B $\frac{1(\text { stress })^{2}}{2}$ The elastic energy stored per unit volume in a stretched wire is $$ \mathrm{u}=\frac{1}{2} \times \text { stress } \times...

### . The linear density of a vibrating string is transverse wave is propagating on the string and is described by the equation where and are measured in meter and t in second. Ten sion in the string is

A

B

C

D

Correct option is A $0.12 \mathrm{~N}$ Linear density $\mu=1.3 \times 10^{4} \mathrm{Kg} / \mathrm{m}$ Wave equation $y=0.021 \sin (x+30 t)$ Velocity of wave...

### 5 mole of oxygen are heated at constant volume from to What will be the change in the internal energy of gas? The molar heat of oxygen at constant pressure, and mol

$\mathrm{R}=8.31 \mathrm{~J} \quad \mathrm{~mol}^{-1} \mathrm{deg}^{-1}=\frac{8.31}{4.18} \mathrm{cal} \mathrm{mol}^{-1} \mathrm{deg}^{-1}$ $=1.99 \mathrm{cal} \mathrm{mol}^{-1} \mathrm{deg}^{-1}$...

### State and explain the law of conservation of angular momentum. Give two examples to illustrare the law

Law of conservation of angular momentum states that in the absence of an external torque, the total angular momentum is conserved or the total angular momentum of an isolated system remains constant...

### Write the law of conservation of angular momentum. Write two examples based on this

When there is no net torque applied to a system, such as a rotating item or objects, the law of conservation of angular momentum asserts that angular momentum is conserved. An ice skater performing...

### The surface area of a black body is and temperature is . How much heat is radiated per minute by it

Stefan's constant = $5 \cdot 67 \times 10^{-8}$ joule $/\left(\mathrm{m}^{2}-\sec -\mathrm{K}^{4}\right)$ The power radiated is given by Stefan's law: $$ \mathrm{P}=\sigma \mathrm{AeT}^{4} $$...

### The angular acceleration of particle moving along a circular path with uniform speed

A uniform but non zero

B zero

C variable

D such as can not be predicted from given information

The correct option is B zero The velocity of the particle is constant i.e $\mathrm{v}=$ constant Using $\mathrm{v}=\mathrm{rw} \quad \Longrightarrow \mathrm{w}=$ constant $\therefore$ Angular...

### What do you mean by centripetal acceleration ? Deduce the formula for centripetal acceleration of a body executing circular motion with uniform velocity in terms of angular velocity

rate of change of tangential velocity is called as the centripetal acceleration. $$ \mathrm{F}=\frac{\mathrm{mv}^{2}}{\mathrm{r}} $$ centripetal acceleration is given by, $$...

### Write Bernoulli’s theorem

Bernoulli's principle asserts that the entire mechanical energy of a moving fluid, which includes gravitational potential energy of elevation, fluid pressure energy, and fluid motion kinetic energy,...

### What is Hooke’s law ?

In the year 1660, an English scientist named Robert Hooke discovered Hooke's law, commonly known as the law of elasticity. "When an object has a relatively minor deformation, the magnitude of the...

### Write down the theorem of perpendicular axes of moment of inertia

The perpendicular axis theorem asserts that the moment of inertia of a planar lamina (i.e. 2-D body) at an axis perpendicular to the plane of the lamina is equal to the sum of the moments of inertia...

### The earth revolves around the sun in a circular path with a speed of . What is the radial acceleration directed towards the sun?

$$ \begin{array}{c} \text { Speed of revolution }=30 \mathrm{Km} / \mathrm{s} \\ =3 \times 10^{4} \mathrm{~m} / \mathrm{s} \end{array} $$ Time of revolution $=$ One year $=356$ days (convert into...

### A wave represented by an equation superimposes with another wave and produces stationary wave. At node is formed. The equation of the second wave is

i)

ii)

iii)

iv)

Correct option is D $-\mathrm{a} \cos (\mathrm{kx}+\omega \mathrm{t})$ To form a stationary wave with $y=a \cos (k x-w t)$ the wave should be in the opposite direction of this wave and amplitude...

### 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

### For total internal reflection to take place, the angle of incidence and the refractive index of the medium must satisfy the inequality

A

B

c

D

Correct option is A $\frac{1}{\sin i}\frac{1}{\mu}$ $$ \Rightarrow \frac{1}{\sin i}

### Total internal reflection can take place only if ?

Total internal reflection can take place only if (1) Light goes from optically denser medium to rarer medium (2) Angle of incidence is greater than the critical angle

### Assertion (A): Propagation of light through an optical fibre is due to total internal reflection taking place at the core-cladding interface. Reason (R) : Refractive index of the material of the core of the optical fibre is greater than that of air.

Both (A) and (R) are true but (R) is not the correct explanation of Propagation of light through an optical fibre is due to total internal reflection taking place at the interface of cable and air....

### In optical fibres, propagation of light is due to which phenomenon ?

Optical fibre is a device which transmits light introduced at one end to the opposite end, with little loss of the light through the sides of the fibre. It is possible with the help of total...

### Name the principle on the basis of which optical fibres work.

Optical fibres works on the principle of total internal reflection. When light ray strikes at the internal surface of optical fibre cable called such that incidence angle is greater than critical...

### Name the physical principle on which the working of optical fibres is based.

The physical principle on which the working of optical fibres is based is, repeated total internal reflection of light.

### Optical fiber communication is based on which of the phenomena:-

Total internal reflection

### The danger signals installed at the top of tall buildings are red in colour. These can be easily seen from a distance because among all other colours, the red light:

The amount of scattering is inversely proportional to the fourth power of wavelength. And since the wavelength of red has the longest wavelength, the amount of scattering becomes smaller. Danger...

### Why Red Signals are used as danger sign? Explain.

Red light is used as danger signal because it is having high wavelength, less scattering ,hence can travel larger distances.

### Derive an expression for energy stored in a charged condenser. Obtain its different forms.

Let 'C' is the capacitance of the capacitor. Let 'Q' and 'V' be the charge and potential difference respectively. Let 'q' be the charge on the capacitor at some stage during charging and 'v' is the...

### Derive an expression for energy stored in a capacitor. In which form energy is stored?

Let us consider a capacitor of capacitance C and potential difference V between the plates. Let the charge on one plate be +q and -q on the other. Suppose the capacitor is being charged gradually....

### State the laws of refraction of light.

Incident ray, reflected ray, refracted ray and the normal of the system lie in the same plane.

### What is meant by refraction of light? State the laws of refraction.

Refraction: The phenomenon of change in the direction of light when it passes from one transparent medium to another is called refraction. Laws of refraction: (i) The incident ray, the refracted ray...

### Describe the reflection of light on the basis of Huygen’s wave theory.

Reflection at plane surface As shown in figure, consider a plane wavefront $A B$ incident on the plane reflecting surface AY, both the wavefront and the reflecting surface being perpendicular to the...

### Explain the problem of refraction of light the basis of Huygen’s secondary wavelets theory and verify Snell’s law of refraction .

Refraction at plane Surface We will now use Huygens principle to device the laws of refraction. Let PP' represent the surface separating medium 1 and medium 2 as shown in figure 12.4. Let...

### Where is the near point of a person suffering from hypermetropia (or long-sightedness)?

Hypermetropia or Long Sightedness is an eye defect. A person suffering from it can see distant objects clearly but is not able to see nearby objects clearly. The near point of a person suffering...

### Complete the following sentence : (I). A short-sighted person cannot see …………… object clearly. Short-sightedness can be correct by using ……….. lenses. (II). A long-sighted person cannot see ………….. object clearly. Long-sightedness can be corrected by using ………… lenses.

(a) A short-sighted person cannot see close objects clearly. Short-sightedness can be corrected by using the concave lens in front of the eyes. (b) A long-sighted person cannot see far objects...

### Write true or false for the following statements : For a person suffering from myopia, the image of the object is formed in front of the retina.

True In myopia person is not able to see far away objects due to elongation of the eyeball . The image is formed in front of the retina as shown in the figure below.

### What is the far point of a person suffering from myopia (or short-sightedness)?

The far point of a person suffering from myopia or short- sightedness is less than infinity. In myopia the person is able to see close by objects clearly but they are not able to see distant objects

### A person having short-sightedness cannot see objects clearly beyond a distance of 1.5 m. What would be the nature and power of the corrective lens used to restore proper vision?

Concave lens should be used to restore proper vision. Calculation of power: Object distance, $u=-\infty$ Image distance, $\mathrm{v}=-1.5 \mathrm{~m}$ $$ \begin{array}{l}...

### What is short-sightedness? State the two causes of short-sightedness (or myopia)

Short Sightedness is that defect of vision due to which a person can see nearby objects clearly but cannot see distant objects clearly. Causes: 1. Excessive curvature of the eye lens 2. Elongation...

### Does short-sightedness (myopia) or long-sightedness (hypermetropia) imply necessarily that the eye has partially lost its ability of accommodation? If not, what might cause these defects of vision?

The ability of the eye lens to adjust its focal length is called accommodation. No, short-sightedness (myopia) or long-sightedness (hypermetropia) does not imply necessarily that the eye has...

### Long-sightedness is to hypermetropia as short-sightedness is to :

Long-sightedness is also called hypermetropia short-sightedness is also called myopia

### What is a long-sighted eye ? State one cause of long-sightedness. Name the lens used for correcting long-sightedness.

An eye is said to be long-sighted if the image of a nearby object is formed behind the retina. It is caused because the eye lens cannot widen enough to reduce the focal length i.e. it is too thin or...

### A man can see objects clearly up to 3m. What type of lens he should use in order to see clearly up to 12m?

Clearly, the lens used should be the concave lens. Actual far point $$ \mathrm{u}=-12 \mathrm{~m} $$ Far point of the person, $$ \mathrm{v}=-3 \mathrm{~m} $$ We have lens formula, $$...

### A person suffering from myopia cannot see beyond . What should be the focal length of the concave lens that will correct his vision?

So when the object is placed at infinity a image should be formed at $1 \mathrm{~m}$ away from eyes. So, $u=\infty$ $$ \mathrm{v}=-1 \mathrm{~m}=-100 \mathrm{~cm} $$ we know that...

### Give reasons: A concave lens is used to correct myopia.

In a myopic eye, the image of a distant object is formed in front of the retina and not at the retina itself. A concave(diverging) lens causes light rays to diverge before they strike the lens of...

### Which of the following lens is used to minimise myopia?

A Convex lens

B Concave lens

c Cylindrical lens

D Planar lens

Correct option is (B) Concave lens Near-sightedness, also known as short-sightedness and myopia, is a condition of the eye where light focuses in front of, instead of on, the retina. This causes...

### Which of the following lens is used to correct myopia?

A Convex lens

B Concave lens

C Cylindrical lens

D None of these

Correct option is B Concave lens In Myopia, the image of a nearby object is formed ahead of the retina. By placing a concave (negative powered) lens in front of a myopic eye, the image is moved...

### To remove hypermetropia lens used is –

(A) Convex

(B) Concave

(C) Cylindrical

(D) Plano-convex

Correct option is (A)Convex lens In Hypermetropia, the image of a nearby object is formed behind the retina. By placing a convex (plus powered) lens in front of a hypermetropic eye, the image is...

### Establish the laws of reflection of light on the basis of wave theory.

The reflected wave front must be built in the following manner, as shown in Figure: - I Draw an arc of a circle with a radius equal to DE from B as the centre. (ii) Draw the tangent EF to the arc...

### What do you mean by -type and -type semiconductors ? Explain the working of a junction diode.

Extrinsic P-Type Semiconductors are made when a small amount of a trivalent impurity is added to a pure semiconductor, resulting in a significant number of holes. The addition of trivalent...

### What is the use of a step-up transformer?

In generating stations and other power transmission applications, step up transformers are commonly utilised. The lower voltage is provided to the primary windings of power transformers at power...

### What do you mean by intensity of electric field ?

The electric field is the area around an electric charge where its impact can be felt. The field of electricity The force experienced by a unit positive charge put at a certain point is called...

### Explain end-on position and broad side-on position of a bar magnet.

Consider a bar magnet of length 2l and pole strength m. Suppose a point P on the axis of the magnet at a distance d from its center. (d –l) is the distance of P form the N-pole of the magnet.

### What do you mean by magnetic elements of the earth ?

The magnetic declination, magnetic dip, and magnetic intensity or one of its components at any location on the earth's surface are all magnetic elements.

### What is the principle of conservation of charge?

The overall quantity of electric charge in a system does not change over time, according to the conservation of charge principle. Charged particles can be generated at the subatomic level, but only...

### What is light year ?

A light-year is the distance light travels in one Earth year.