Electromagnetic Induction — Previous-Year Questions

Q1. A circular loop of radius 0.1 m is placed in a uniform field B = 0.5 T at 60° to the area-normal. The flux is:

Q2. Flux through a closed surface containing a bar magnet is:

Q3. A 20-turn coil of area 50 cm² is placed in B = 0.4 T parallel to the area-vector. Total flux linkage:

Q4. Flux is MAXIMUM when:

Q5. Unit of magnetic flux can also be written as:

Q1. A 100-turn coil has its flux change from 0.05 Wb to 0.01 Wb in 0.02 s. EMF induced is:

Q2. Doubling the rotation speed of a generator coil doubles:

Q3. A magnet falls through a vertical copper pipe. It slows because of:

Q4. Flux through a coil is Φ(t) = 3t² + 4t. EMF at t = 2 s is:

Q5. Faraday's law applies to:

Q6. A 50-turn coil of area 100 cm² rotates at 60 Hz in B = 0.5 T. Peak EMF is:

Q1. A bar magnet's N-pole approaches a stationary coil. The end of the coil facing the magnet becomes:

Q2. Lenz's law is a consequence of:

Q3. When a magnet is pulled AWAY from a coil, the induced current:

Q4. Eddy currents are minimised in transformer cores by:

Q5. A magnet is dropped into a vertical copper tube. Compared to free-fall, the descent is:

Q1. A rod of length 1 m moves at 5 m/s perpendicular to B = 0.4 T. EMF between its ends:

Q2. The rod in the previous question is connected through rails to a 4 Ω external resistor. Current is:

Q3. Same setup — magnetic braking force on the rod is:

Q4. A rod slides on frictionless rails (B = 0.5 T, L = 0.4 m, R = 2 Ω) at constant 3 m/s. External force needed to keep v constant:

Q5. Energy dissipated per second in the previous question is supplied by:

Q1. A uniform B(t) inside a cylindrical region of radius 0.1 m increases at 2 T/s. Induced E at r = 0.05 m is:

Q2. Same setup — E at the boundary r = 0.1 m:

Q3. The induced electric field due to a changing magnetic flux is:

Q4. Induced E field lines are:

Q5. Outside a cylindrical region of changing B, the induced E:

Q1. A solenoid of 500 turns, length 0.25 m, area 4 × 10⁻⁴ m². Self-inductance:

Q2. If the turns of a solenoid are doubled keeping length and area unchanged, L becomes:

Q3. An inductor of 0.5 H carries a current of 4 A. Energy stored:

Q4. In an RL circuit (R = 4 Ω, L = 0.2 H), the time constant is:

Q5. Why is a flyback diode placed across a relay coil?

Q1. Current in the primary of two coupled coils changes from 0 to 4 A in 0.1 s. EMF in secondary is 20 V. Mutual inductance is:

Q2. Coils with L₁ = 4 H, L₂ = 9 H are coupled with k = 0.5. Mutual inductance is:

Q3. Two coaxial solenoids: outer has N₁ = 1000 turns, inner N₂ = 200, common area 1 × 10⁻³ m², length 0.5 m. Mutual inductance:

Q4. Mutual inductance between two coils depends on:

Q5. If the secondary of an ideal transformer (N_s = 200, N_p = 100) is fed 50 V on the primary, V_s is:

Q1. Why are transformer cores LAMINATED rather than solid?

Q2. A solid metal pendulum swings between magnet poles and quickly stops. The same pendulum with a SLOTTED bob continues swinging. The reason is:

Q3. Induction cooktops heat a pan by:

Q4. Eddy-current losses in a magnetic core depend on lamination thickness t as:

Q5. Electromagnetic brakes on a high-speed train: