Electromagnetic Induction Physics - Electromagnetic Induction

In the diagram shown if a bar magnet is moved along the common axis of two single turn coils A and B in the direction of arrow then-

The self-inductance of a solenoid is L. Keeping the length and area same, the number of turns in the coil is increased to two times. The self-inductance of the solenoid will now be-

A coil of area 80cm² and number of turns 50 is rotating about an axis perpendicular to a magnetic field of 0.05 Tesla at 2000 rotations per minute. The maximum value of emf induced in it will be.

Two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b ), (c) and (d) as given below.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and Rare true but R is NOT the correct explanation of A.
3. A is true but R is false.
4. A is false and R is also false.

Assertion (A): Tile coil in the resistance boxes are made by doubling the wire.
Reason (R): Thick wire is required in resistance box.

Two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b ), (c) and (d) as given below.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and Rare true but R is NOT the correct explanation of A.
3. A is true but R is false.
4. A is false and R is also false.

Assertion (A): An aircraft flies along the meridian, the potential develops at the ends of its wings.
Reason (R): Whenever there is change in the magnetic flux e.m.f. induces.

Two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b ), (c) and (d) as given below.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and Rare true but R is NOT the correct explanation of A.
3. A is true but R is false.
4. A is false and R is also false.

Assertion (A): When number of turns in a coil doubled, coefficient of self inductance of the coil becomes four times.
Reason (R): Coefficient of self inductance is proportional to the square of number of turns.

Two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b ), (c) and (d) as given below.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and Rare true but R is NOT the correct explanation of A.
3. A is true but R is false.
4. A is false and R is also false.

Assertion (A): An artificial satellite with a metal surface is moving above the earth in a circular orbit. A current will be induced in satellite if the plane of the orbit is inclined to the plane of the equator.
Reason (R): The current will be induced only when the speed of satellite is more than 8km/ sec.

Two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b ), (c) and (d) as given below.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and Rare true but R is NOT the correct explanation of A.
3. A is true but R is false.
4. A is false and R is also false.

Assertion (A): An induced current is developed when the number of magnetic lines of force associated with conductor is changed.
Reason (R): An induced current develop in a conductor moved in a direction parallel to the magnetic field.

A long straight current carrying wire passes normally through the centre of circular loop. If the current through the wire increases, will there be an induced emf in the loop? Justify.

What is the direction of induced currents in metal rings 1 and 2 when current I in the wire is increasing steadily?

A conducting loop is held below a current carrying wire PQ as shown. Predict the direction of the induced current in the loop when the current in the wire is constantly increasing.

Current in a circuit falls from 5.0A to 0.0A in 0.1s. If an average emf of 200V induced, give an estimate of the self-inductance of the circuit.

Use Lenz’s law to determine the direction of induced current in the situations described by Fig.

1. A wire of irregular shape turning into a circular shape;

2. A circular loop being deformed into a narrow straight wire.

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A 1.0m long metallic rod is rotated with an angular frequency of 400 rad s^–1 about an axis normal to the rod passing through its one end. The other end of the rod is in contact with a circular metallic ring. A constant and uniform magnetic field of 0.5T parallel to the axis exists everywhere. Calculate the emf developed between the centre and the ring.

Consider Experiment 6.2. (a) What would you do to obtain a large deflection of the galvanometer? (b) How would you demonstrate the presence of an induced current in the absence of a galvanometer?

State the underlying principle of a transformer.How is the large scale transmission of electric energy over long distances done with the use of transformers?

A horizontal straight wire 10m long extending from east to west is falling with a speed of 5.0ms^–1, at right angles to the horizontal component of the earth’s magnetic field, 0.30 × 10^–4Wbm^–2.

1. What is the instantaneous value of the emf induced in the wire?
2. What is the direction of the emf?
3. Which end of the wire is at the higher electrical potential?

A rectangular wire loop of sides 8cm and 2cm with a small cut is moving out of a region of uniform magnetic field of magnitude 0.3T directed normal to the loop. What is the emf developed across the cut if the velocity of the loop is 1 cms^–1 in a direction normal to the:

1. Longer side,
2. shorter side of the loop?

For how long does the induced voltage last in each case?

An air-cored solenoid with length 30cm, area of cross-section 25cm² and number of turns 500, carries a current of 2.5A. The current is suddenly switched off in a brief time of 10^–3s. How much is the average back emf induced across the ends of the open switch in the circuit? Ignore the variation in magnetic field near the ends of the solenoid.

A circular coil of radius 8.0cm and 20 turns is rotated about its vertical diameter with an angular speed of 50rad s^–1 in a uniform horizontal magnetic field of magnitude 3.0 × 10^–2T. Obtain the maximum and average emf induced in the coil. If the coil forms a closed loop of resistance 10Ω, calculate the maximum value of current in the coil. Calculate the average power loss due to Joule heating. Where does this power come from?

Sunita and her friends visited an exhibition. The policeman asked them to pass through a metal detector. Sunita’s friends were initially scared of it. Sunita, however, explained to them the purpose and working of the metal detector.
Answer the following questions:

1. On what principle does a metal detector work?
2. Why does the detector emit sound when a person carrying any metallic object walks through it?
3. State any two qualities which Sunita displayed while explaining the purpose of walking through the detector.

A conducting loop is held above a current carrying wire ‘PQ’ as shown in the figure. Depict the direction of the current induced in the loop when the current in the wire PQ is constantly increasing.

Ram is a  student of class X in a village school. His uncle gifted him a bicycle with a dynamo fitted in it. He was very excited to get it. While cycling during night, he could light the bulb and see the objects on the road. He however, did not know this device works. He asked this question to his teacher. the teacher considered it an opportunity to explain the working to the whole class.
Answer the following question:

1. State the principle and working of a dynamo.
2. Write two values each displayed by Ram and his school teacher.

A metallic loop is placed in a nonuniform magnetic field. Will an emf be induced in the loop?

1. Obtain an expression for the mutual inductance between a long straight wire and a square loop of side a as shown in Fig.
2. Now assume that the straight wire carries a current of 50A and the loop is moved to the right with a constant velocity, v = 10\m/s. Calculate the induced emf in the loop at the instant when x = 0.2m. Take a = 0.1m and assume that the loop has a large resistance.

Figure shows a metal rod PQ resting on the smooth rails AB and positioned between the poles of a permanent magnet. The rails, the rod, and the magnetic field are in three mutual perpendicular directions. A galvanometer G connects the rails through a switch K. Length of the rod = 15cm, B = 0.50T, resistance of the closed loop containing the rod = 9.0mΩ. Assume the field to be uniform.

1. Suppose K is open and the rod is moved with a speed of 12cms^-1 in the direction shown. Give the polarity and magnitude of the induced emf.

2. Is there an excess charge built up at the ends of the rods when K is open? What if K is closed?
3. With K open and the rod moving uniformly, there is no net force on the electrons in the rod PQ even though they do experience magnetic force due to the motion of the rod. Explain.
4. What is the retarding force on the rod when K is closed?
5. How much power is required (by an external agent) to keep the rod moving at the same speed (= 12cms^–1) when K is closed? How much power is required when K is open?\
6. How much power is dissipated as heat in the closed circuit? What is the source of this power?
7. What is the induced emf in the moving rod if the magnetic field is parallel to the rails instead of being perpendicular?

Suppose the loop in Exercise 6.4 is stationary but the current feeding the electromagnet that produces the magnetic field is gradually reduced so that the field decreases from its initial value of 0.3T at the rate of 0.02T s^–1. If the cut is joined and the loop has a resistance of 1.6Ω, how much power is dissipated by the loop as heat? What is the source of this power?

It is desired to measure the magnitude of field between the poles of a powerful loud speaker magnet. A small flat search coil of area 2cm² with 25 closely wound turns, is positioned normal to the field direction, and then quickly snatched out of the field region. Equivalently, one can give it a quick 90º turn to bring its plane parallel to the field direction). The total charge flown in the coil (measured by a ballistic galvanometer connected to coil) is 7.5mC. The combined resistance of the coil and the galvanometer is 0.50Ω. Estimate the field strength of magnet.

A long solenoid with 15 turns per cm has a small loop of area 2.0 cm² placed inside the solenoid normal to its axis. If the current carried by the solenoid changes steadily from 2.0A to 4.0A in 0.1s, what is the induced emf in the loop while the current is changing?

The ____________ motion between the magnet and the coil is responsible for generation (induction) of electric current in the coil.