Daily Practice Problems

Class 12 Physics

Electromagnetic Induction

Class 12 Physics

Electromagnetic Induction

**Question 1:**

The phenomenon called electromagnetic induction was first investigated by

- Newton
- Kepler
- Faraday
- Galileo

**Question 2:**

The basic requirement for inducing e.m.f in a coil is that

- Flux should link the coil
- There should be change in flux linking with the coil
- Coil should form a closed loop
- None of these

**Question 3:**

A circuit has inductance of 2H. If the circuit current changes at the rate of 10 A/ second, then self-induced e.m.f. is ………..

(a) 5V

(b) 0.2 V

(c) 20 V

(d) 10 V

**Question 4:**

Two identical loops, one of copper and another of constantan are removed from a magnetic field within the same time interval. In which loop will be induced current be greater?

**Question 5:**

Define one Henry.

**Question 6:**

The induced emf is sometimes known as ‘Back emf’ why?

**Question 7:**

How is the mutual inductance of a pair of coil affected when:

- Separation between the coil is increased?
- The number of turns of each coil is increased?

Explain your answer in each case.

**Question 8:**

Two coils have mutual inductance of 1.5 henry. If current in primary circuit is raised to 5 amperes in one ms after closing the circuit. What is the emf induced in the secondary?

**Question 9:**

A wheel with 10 metallic spokes each 0.5 m long is rotated with a speed of 120 rev/min in a plane normal to the horizontal component of earth’s magnetic field H_{E }at a place. If H_{E}= 0.4 G at the place, what is the induced emf between the axle and the rim of the wheel? Note that 1 G = 10^{–4} T.

**Question 10:**

A circular coil of radius 10 cm, 500 turns and resistance 2 Ω is placed with its plane perpendicular to the horizontal component of the earth’s magnetic field. It is rotated about its vertical diameter through 180° in 0.25 s. Estimate the magnitudes of the emf and current induced in the coil. Horizontal component of the earth’s magnetic field at the place is 3.0 × 10–5 T.

**Question 11:**

Two spherical bobs, one metallic and the other of glass, of the same size are allowed to fall freely from the same height above the ground. Which of the two would reach earlier and why?

**Question 12:**

A coil of inductance 0.25 H is connected to 18 V battery. Calculate the rate of growth of current?

**Question 13:**

Self-induction of an air core inductor increases from 0.01 mH to 10 mH on introducing an iron core into it. What is the relative permeability of the core used?

**Question 14:**

State Lenz’s law. A metallic rod held horizontally along east-west direction, is allowed to fall under gravity. Will there be an emf induced at its ends?

**Question 15:**

Two concentric circular coils, one of small radius r_{1} and the other of large radius r_{2}, such that r_{1}<< r_{2}, are placed co-axially with centres coinciding. Obtain the mutual inductance of the arrangement.

**Question 16:**

The motion of copper plate is damped when it is allowed to oscillate between the pole pieces of a magnet. State the cause of this damping.

**Question 17:**

Obtain the expression for the magnetic energy stored in a solenoid in terms of magnetic field B, area A and length l of the solenoid.

**Question 18:**

State Faraday’s Law of electromagnetic induction

Smita peddles a stationary bicycle. The pedals of the bicycle are attached to a 100 turn coil of area 0.10 m^{2}. The coil rotates at half a revolution per second and it is placed in a uniform magnetic field of 0.01 T perpendicular to the axis of rotation of the coil. What is the maximum voltage generated in the coil?

**Question 20:**

An electromagnet has stored 648 J of magnetic energy, when a current of 9 A exists in its coils. What average emf is induced if the current is reduced to 0 in 0.45 s?

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