Board-style MCQs and past-paper numericals in the BIEK / Sindh Board pattern. Tap an option to check yourself instantly. Solved questions are at the bottom.
Multiple-choice questions
Solved numericals (past papers)
EMF from a changing magnetic flux
The flux through a coil of 200 turns changes from 0.05 Wb to 0.01 Wb in 0.2 s. Find the average induced EMF.
ε = −N (ΔΦ/Δt) = −200 × (0.01 − 0.05)/0.2 = −200 × (−0.04/0.2)
= −200 × (−0.2) = 40 V
Motional EMF of a moving rod
A 0.40 m rod moves at 5 m/s perpendicular to a field B = 0.30 T. Find the EMF induced.
ε = BLv = 0.30 × 0.40 × 5 = 0.60 V
Magnetic flux through a coil
A coil of area 2 × 10⁻² m² sits in a field B = 0.50 T with its plane at 60° to the field. Find the flux. (θ = angle between B and the normal = 30°)
Φ = BA cosθ = 0.50 × 2 × 10⁻² × cos30° = 0.50 × 0.02 × 0.866
= 8.66 × 10⁻³ Wb
Self-inductance from EMF
An EMF of 8 V is induced in a coil when the current changes at 40 A/s. Find the self-inductance L.
ε = L (dI/dt) → L = ε / (dI/dt) = 8 / 40 = 0.2 H
Mutual inductance between two coils
A current changing at 50 A/s in one coil induces a 5 V EMF in a neighbouring coil. Find the mutual inductance M.
ε = M (dI/dt) → M = ε / (dI/dt) = 5 / 50 = 0.1 H
Transformer turns & current
An ideal transformer steps 220 V down to 11 V. The primary has 2000 turns and draws power that delivers 4 A in the secondary. Find N_s and the primary current I_p.
N_s/N_p = V_s/V_p → N_s = 2000 × (11/220) = 100 turns
I_p V_p = I_s V_s → I_p = (I_s V_s)/V_p = (4 × 11)/220 = 0.2 A