RI Y6 Remedial EMI Soln

Raffles Institution Year 5-6 Physics Department 1 2025 Year 6 H2 Physics Remedial Chapter 17: Electromagnetic Induction Suggested Solutions 1 (a) (i) (ii) (b) (i) BL yφ∆= ∆ (ii) Average e.m.f. induced, T BL yE BLvtt φ∆∆= = =∆∆ (iii) Induced current TBLvEI RR= = At constant speed, net force = 0 B T T F Mg BIL Mg BLvB L MgR MgRv BL = =  = = 22 (c) Non-continuous operation: rod would reach the bottom and then have to be returned to its original height to start again. 2 (a) From graph, when x = 5.0 cm, B = 50 mT Φ = NBA = (150)(50 x 10-3)(0.40 x 10-4) = 3.0 x 10-4 Wb (shown) (b) (i) |∆Φ| = N(|∆B|)A = (150)(50 x 10-3 – 8.0 x 10-3)(0.40 x 10-4) = 2.52 x 10-4 Wb (ii) |ε| = |∆Φ| / ∆t = (2.52 x 10-4) / (0.30) = 8.4 x 10-4 V weight magnetic force weight

Raffles Institution Year 5-6 Physics Department 2 (c) Flux linkage decreases at a decreasing rate as distance i ncreases, so speed must increase to keep rate of change constant. (d) The solenoid may act as a transmitter that generates a changing magnetic flux. Since the small coil is linked to the changing magnetic flux, by Faraday’s Law, an induc ed e.m.f. will be produced in the small coil which can be used to charge up the battery in the mobile phone. [TPJC/Prelims 2014/P3/3] 3 (a) Whenever there is a change in magnetic flux linkage of a circuit or coil, an e.m.f. is induced in the circuit and the magnitude is directly proportional to the rate of change of magnetic flux linkage of the circuit or coil. (b) Φ = NBA = 800 x 5.0 x 10-2 x 2.5 x 10-2 = 1.0 Wb (c) (i) Φ = NBA cos ωt where ωt = 0 when t = 0 (eqn can be deduced from graph given) e.m.f. = - dΦ dt = - NBA dcos ωt dt = - NBAω (- sin ωt) Max e.m.f. = NBAω = 1.0 x ( 2π 1.0x10-3 ) = 6280 V Alternative method: Max. e.m.f. = - (max. gradient) = - (1.5 - 0) (0 - 0.25)x10-3 = 6000 V {accept 5400 to 6600 V} (ii) positive sine graph of any amplitude same period as the flux linkage (d) As the coil turns, the magnetic flux linkage decreases. By Right-hand Grip Rule , the current will flow in the direction PQRS so as to enhance the magnetic flux linkage. Φ/Wb

Raffles Institution Year 5-6 Physics Department 3 4 (a) (i) Shows decreasing amplitude throughout Period same or slightly longer (up to 1.5 T) (ii) Faraday’s law state that the magnitude of the induced emf in a conductor (or circuit) is directly proportional to the rate of change of magnetic flux linkage experienced by the conductor (or linking the circuit). When the electromagnet is switched on, as current flows through the coil, it generates a magnet