Physics 9702 · AS & A Level · Damped and forced oscillations, resonance
Damped and forced oscillations, resonance — practice question
A bar magnet is hung from the free end of a helical spring, as shown in Fig. 3.1. One pole of the magnet is placed inside a coil of wire. The coil is connected in series with a switch and a resistor. The switch is open. The magnet is moved vertically and then let go. As the magnet passes through its rest position, a timer is started. Fig. 3.2 shows how the vertical displacement y of the magnet from its rest position varies with time t. At time t = 4.0\,\text{s}, the switch is closed.
(a(i))[1]
Use Fig. 3.2 to state the evidence that the magnet is undergoing free oscillations during the period t = 0 to t = 4.0\,\text{s}.
(a(ii))[2]
State, with a reason, whether the damping after time t = 4.0\,\text{s} is light, critical or heavy.
(a(iii))[2]
Determine the natural frequency of oscillation of the magnet on the spring.
(b(i))[2]
State Faraday’s law of electromagnetic induction for this situation.
(b(ii))[4]
Explain why the amplitude of vibration of the magnet decreases after time t = 4.0\,\text{s}.
Worked solution & mark scheme
This 11-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Amplitude is unchanged” …