Chapter 3 · Faraday's laws, mutual & self induction: practice questions

The iron core of a transformer is built from thin laminated sheets insulated from one another mainly to…

• Araise the frequency of the alternating current
• Bincrease the eddy currents in the core
• Creduce the energy lost as heat by eddy currents
• Dincrease the ohmic resistance of the primary coil

A straight conducting rod of length L moves with velocity v perpendicular to a uniform magnetic field of flux density B. The motional electromotive force induced across the rod is given by…

• AL v / B
• BB L v
• CB v / L
• DB L / v

In an AC generator, the instantaneous induced emf reaches its maximum value at the instant when the plane of the coil is…

• Aparallel to the magnetic field lines
• Bat an angle of 45° to the field lines
• Cperpendicular to the magnetic field lines
• Dcompletely outside the magnetic field

Eddy currents are usefully employed in…

• Athe electromagnetic braking system of trains
• Bincreasing the resistance of transmission cables
• Cinsulating the windings of a coil
• Dstoring electric charge in a capacitor

A conducting rod of length 0.5 metre slides at 4 m/s along parallel rails placed in a magnetic field of flux density 0.2 T. If the circuit has a total resistance of 2 Ω, the induced current in the rod equals…

• A0.4 A
• B0.1 A
• C0.8 A
• D0.2 A

A coil of area 0.02 m² is placed in a uniform magnetic field of flux density 0.4 T so that the normal to its plane makes an angle of 60° with the field. The magnetic flux Φₘ through the coil equals…

• A4×10⁻³ Wb
• B2×10⁻³ Wb
• C6.9×10⁻³ Wb
• D8×10⁻³ Wb

A coil of self-inductance 2 H carries a current that increases uniformly from 3 A to 7 A in 0.5 s. The magnitude of the self-induced emf is…

• A8 V
• B16 V
• C32 V
• D12 V

A solenoid of 200 turns carries a current of 4 A, producing a magnetic flux Φₘ of 0.02 Wb through each turn. The self-inductance coefficient L of the solenoid equals…

• A1 H
• B0.5 H
• C10 H
• D2 H

A square coil of side 0.1 metre and 80 turns lies perpendicular to a magnetic field. The flux density increases uniformly from 0.2 T to 0.7 T in 0.05 s. The magnitude of the induced electromotive force equals…

• A0.8 V
• B16 V
• C4 V
• D8 V

Two coils are wound on the same core. When the current in the primary changes from 2 A to 6 A in 0.1 s, the flux linking each of the 300 turns of the secondary changes by 8 × 10⁻⁴ weber. The mutual inductance and the induced secondary emf are respectively…

• AM = 0.06 H, emf = 24 V
• BM = 0.6 H, emf = 24 V
• CM = 0.6 H, emf = 2.4 V
• DM = 0.06 H, emf = 2.4 V