Physics (AS & A Level) · May / June 2017 · Paper 42 · Question 3

A bar magnet of mass 250 g is suspended from the free end of a spring, as illustrated in Fig. 3.1. spring magnet coil Fig. 3.1 The magnet hangs so that one pole is near the centre of a coil of wire. The coil is connected in series with a resistor and a switch. The switch is open. The magnet is displaced vertically and then allowed to oscillate with one pole remaining inside the coil. The other pole remains outside the coil. At time t = 0, the magnet is oscillating freely as it passes through its equilibrium position. At time t = 6.0 s, the switch in the circuit is closed. 9 The variation with time t of the vertical displacement y of the magnet is shown in Fig. 3.2. –2.0 –1.5 –1.0 –0.5 0 0.5 1.0 y / cm 1.5 2.0 0 2 4 6 8 10 12 14 16 t / s Fig. 3.2

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