Question Pool Electromagnetic Induction

# Electromagnetic Induction - SAMAGRA Question Pool & Answers | Class 12

Kerala Syllabus SAMAGRA SCERT SAMAGRA Question Pool for Class 12 Physics Electromagnetic Induction

Qn 1.

Inertia of the circuit is the cause of self inductance of a coil

1. What happens to the value of L of the coil when the no. of turns is doubled keeping all other parameters constant ?

2. An induced emf of 4V is generated when the current in the circuit changes from 3 A to 4A in one millisecond. What is the self inductance of the coil

3. A bar magnet is allowed to fall freely through a solenoid whose ends are connected to each other. Does its acceleration is less than g ? Justify your answer

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Qn 2.

A boy is riding a bicycle with its dynamo on. when he increases the speed, the brightness of the bulb connected to the dynamo increases

1. State the law used to explain the above phenomenon.

2. Which law helps you to find the direction of current induced in the loop ?

3. The magnetic flux through a coil is E = (5t2+6t+9) Wb. Find the ratio of emf at t = 3 s

to t = 0 s

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Qn 3.

Self inductance of a coil plays the role of inertia in a circuit

(a)The SI unit of self inductance is ......................

(b)Current in a circuit falls from 5A to 1A in 0.1s.If an average EMF of 200V is induced. Find the self inductance of the coil.

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Qn 4.

An a.c. generator consists of a coil of 10,000 turns and of area 100 cm2. The coil rotates at an angular speed of 140 rpm in a uniform magnetic field of 3.6 × 10−2 T. Find the maximum value of the emf induced.

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Qn 5.

Lenz’s law is in accordance with the law of

(a) conservation of charges

(b) conservation of flux

(c) conservation of momentum

(d) conservation of energy

(d) conservation of energy

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Qn 6.

The inductance coils are made of copper. Why?

The induced current will be large in copper since its resistance is very

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Qn 7.

An iron bar falling vertically through the hollow region of a thick cylindrical shell made of copper, experiences a retarding force. What will be the nature of the iron bar.Explain.

The iron bar will be a magnet. When the bar magnet falls eddy current produced in the shell .By Lenz's law, this currents oppose the fall of the magnet

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Qn 8.

A rectangular loop and circular loop are moving out of a uniform magnetic field region to a field free region, with a constant velocity. In which loop do you expect the induced e.m.f to be constant during the passage out of the field region? The field is normal to the loops?

The induced e.m.f. will be constant in the rectangular loop.Because he rate of change of area is  constant in this

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Qn 9.

A closed conducting loop moves normal to the electric field between the plates of a large capacitor. Is a current induced in the loop when it is

(i) wholly inside the capacitor,

(ii) partially outside the plates of the capacitor?

(iii)The electric field is normal to the plane of the loop.

In all the three cases current will not be induced since the coil is moving through the  electric

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Qn 10.

A conducting loop is held stationary, normal to the field, between the N-S poles of a fixed permanent magnet. By choosing a magnet sufficiently strong, can we  generate current in the loop ?.Explain

No. Current will be produced only when the magnetic flux associated with the circuit

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Qn 11.

Match the following

 A B a Lenz’s law Blv b Energy stored in an inductor c Motional emf Electrical Inertia d Inductance ½ LI2 ½ cv2

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Qn 12.

AC generator is a device based on electromagnetic induction used to convert mechanical energy in to electrical energy

a] Draw a graph showing variation of induced emf over a cycle. Also indicate peak value of emf ?

b] How peak value of emf is related to its rms value ?

c] A rectangular wire loop of side 4cmX6cm has 50 turns uniformly from 0.1 Tesla to 0.3 Tesla in 6x10-2 second. Calculate induced emf in the coil

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Qn 13.

Inertia of the circuit is the cause of self inductance of a coil

a] SI unit of self inductance is

(i) Hentry (ii) Farad (iii) Volt (iv) Volt/ meter

b] What happens to the value of L of the coil when the no of turns is doubled keeping all other parameters constant ?

c] An induced emf of 4V is generated when the current in the circuit changes from 3 A to 4A in one millisecond. What is the self inductance of the coil

d] A bar magnet is allowed to fall freely through a solenoid whose ends are connected to each other. Does its acceleration is less than g ? Justify your answer

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Qn 14.

Eddy current produced in rails causes smooth breaking of magnetic breaking system in trains

a] How eddy current is produced ?

b] Explain the following with reason

(i) Laminated cores are used in transformers

(ii) Fixed core made of non- magnetic material is used in galvanometers

c] The bob of a simple pendulum is replaced by a magnet and is allowed to oscillate along its length. If a short circuited coil is added so that one pole o/f the magnet passes in and out of it. What happens to the osculation of magnet ? Explain

A] Whenever the magnetic flux linked with the rails (metal piece) changes eddy current is produced

b]

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Qn 15.

A conductor XY is moving through a uniform magnetic field of intensity B as shown in figure

a] Name the emf ?

b] The motion of XY towards right side causes an anticlockwise induced current. What will be the direction of magnetic induction in the region A?

c] The length of the conductor XY is 20cm. It is moving with a velocity 50m/s. perpendicular to the magnetic field. If the induced emf in the conductor is 2V. Find the magnitudes of magnetic field ?

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Qn 16.

A boy is riding a bicycle with its dynamo on. When he increases the speed, the brightness of the bulb connected to the dynamo increases

a] State the law used to explain the above phenomenon.

b] Which law helps you to find the direction of current induced in the loop ?

c] The magnetic flux through a coil is φ = (5t2+6t+9) Wb. Find the ratio of emf at t = 3 s to t = 0 s

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Qn 17.

a] What is Eddy Current? Mention one application on it.

b] An AC source is connected to a coil with negligible resistance and a bub in series as shown in figure. If an iron rod is gradually inserted in the coil, what happens to the brightness of the bulb? Explain

a] Definition of Eddy Current. Anyone Application

b] Bulb becomes less bright. Inductive Reactance (XL = ωL)

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Qn 18.

Motion of a conductor in a magnetic field induces an emf across its ends

a] Write an expression for the emf induced across the ends of a conductor moving right angles to a uniform magnetic field

b] An aeroplane is flying horizontally from west to east with a velocity of 720 km/h. Calculate the e.m.f induced between the ends of its wings having a span of 25 rn. The vertical component of earth's magnetic field at the place is 2.19 x l0-5T

a] ɛ = Blv

b] v = 720 x 5/18 = 200 m/s

ɛ = Blv = 2.19 x l0-5 x 25 x 200 =

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Qn 19.

A transformer is used to change the alternating voltage to a higher or lower value.

a] What is the principle of a transformer?

B] A power transmission line feeds input power of 2300V to a step down transformer with its primary windings having 4000 turns. What should be the number of turns in the secondary in order to get output power at 230V?

a] Mutual Induction

b] vs/vp = Ns/Np

Ns = 400

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Qn 20.

The generation of emf when the magnetic flux associated with a coil changes is known as Electromagnetic Induction.

a] Mention the factors on which the self inductance of a solenoid depends.

b] Calculate the energy stored in an inductor of inductance 50 mH when a current of 2A is passing through it.

a] L = μ0n2AL

Inductance depends on L, A, n and μr

b] U = 1/2 LI2

= 1/2 x 50 x 10

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Qn 21.

a] Choose the wrong option

i. volt = weber/second

ii. weber = henry x ampere

iii. joule = henry x ampere2

iv. volt = weber x second

b] The current in a coil of self inductance 0.1H varies from 2A to 5A in a time of 1 ms. Find the induced emf across the coil.

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Qn 22.

a] Derive an expression for self inductance of a solenoid

b] What do you mean by Eddy Current? Write any two applications of it

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Qn 23.

Motion of a conductor in a magnetic field induces an emf across its ends.

a] Write an expression for the emf induced across the ends of a conductor moving right angles to a uniform magnetic field

b] An aeroplane is flying horizontally from west to east with a velocity of 720 km/h. Calculate the emf induced between the ends of its wings having a span of 25m. The vertical component of earth’s magnetic field at the place is 2.19 x 10 -5 T.

a] ε = Blv

b] v = 720 x 5/18 = 200 ms-1

ε = Blv = 2.19 x 10 -5 x 25 x 200 =

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Qn 24.

a] Which of the following galvanometer shows larger deflection when tapping key is pressed suddenly?

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Qn 25.

For many purposes, it is necessary to change an alternating voltage from one value to another. This is done with a transformer.

a] The basic principle behind a transformer is ..............................

b] Give an expression for the voltage and current in a transformer