Electromagnetic Induction quiz

The SI unit of magnetic flux is:

Lenz's law is a consequence of conservation of:

Faraday's law states that induced emf equals:

The SI unit of inductance is:

The energy stored in an inductor L carrying current I is:

The motional emf in a rod of length l moving with velocity v perpendicular to field B is:

An AC generator converts:

Eddy currents in a transformer core are reduced by:

The self-inductance of a long solenoid is proportional to:

In an AC generator, the emf is maximum when the plane of the coil is:

Why is self-inductance called the inertia of electricity? (2 marks)

What is the direction of induced current when the north pole of a magnet is moved away from a coil? (2 marks)

Write the expression for the mutual inductance of two long coaxial solenoids. (2 marks)

Why does a spark appear when a switch in an inductive circuit is opened? (2 marks)

How is electromagnetic damping used in galvanometers? (2 marks)

State two factors on which the mutual inductance of two coils depends. (2 marks)

Why is the induced emf in a coil rotating in a field sinusoidal? (2 marks)

Is there an induced emf in a closed loop moving with uniform velocity in a uniform magnetic field? Explain. (2 marks)

Explain the working of induction furnaces. (2 marks)

Why are the cores of electric motors and transformers laminated? (2 marks)

The flux linked with each turn of a 200-turn coil is 6 x 10^-3 Wb and it falls to zero in 0.02 s. Find the average induced emf. (3 marks)

A jet plane with a wing span of 25 m travels west at 1,800 km/h. The Earth's magnetic field is 5 x 10^-4 T and the angle of dip is 30 degrees. Find the emf between the ends of the wings. (3 marks)

Find the self-inductance of a solenoid with 500 turns, length 0.5 m and cross-sectional area 1 x 10^-3 m^2 (mu0 = 4 pi x 10^-7 T m/A). (3 marks)

When the current in a coil changes from 2 A to 4 A in 0.05 s, an emf of 8 V is induced. Find the self-inductance of the coil. (3 marks)

Find the energy stored in an inductor of 50 mH carrying a current of 2 A. (3 marks)

Read the passage and answer the questions. An induction cooktop has a coil under its glass surface carrying a high frequency alternating current. A steel pan placed on it heats up, but the glass stays cool. (i) Which phenomenon heats the pan? (ii) Why does the glass not heat up? (iii) Why is a high frequency current used? (5 marks)

Read the passage and answer the questions. High speed trains and some metros use electromagnetic brakes. Strong electromagnets near the metal wheels or rails produce currents that slow the train smoothly. (i) What currents are produced? (ii) How do they produce a braking force? (iii) Why is this braking smooth? (5 marks)

Read the passage and answer the questions. Airport metal detectors send pulses of current through a coil. When a metal object passes through, it changes the signal received by the detector. (i) What is induced in the metal object? (ii) How does it affect the detector coil? (iii) Name the principle involved. (5 marks)

Read the passage and answer the questions. A hydroelectric generator has a coil of 500 turns, each of area 0.2 m^2, rotating at 50 revolutions per second in a field of 0.1 T. (i) Write the expression for the instantaneous emf. (ii) Find the peak emf. (iii) What is the frequency of the AC produced? (5 marks)

Read the passage and answer the questions. A student drops a strong magnet through a vertical copper pipe and another identical magnet through a PVC pipe of the same size. The magnet in the copper pipe takes much longer to fall. (i) Why is the magnet slowed in copper? (ii) Why is there no effect in PVC? (iii) What happens to the lost gravitational potential energy? (5 marks)

Describe Faraday's experiments on electromagnetic induction with diagrams and state the laws derived from them. (6 marks)

Derive the expression for motional emf in a conductor moving in a magnetic field, and show that the mechanical power supplied equals the electrical power dissipated. (6 marks)

Derive the expression for the self-inductance of a long solenoid and the energy stored in an inductor. (6 marks)

Define mutual inductance and derive an expression for the mutual inductance of two long coaxial solenoids. Show that M12 = M21. (6 marks)

Explain the principle, construction and working of an AC generator with a diagram. Derive the expression for the instantaneous emf. (6 marks)