Physics 9702 · AS & A Level · Damped and forced oscillations, resonance
Damped and forced oscillations, resonance — practice question
A bar magnet hangs from the free end of a helical spring, as shown in Fig. 3.1. One pole of the magnet is 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 released. As the magnet passes through its equilibrium position, a timer is started. Fig. 3.2 shows how the vertical displacement y of the magnet from its equilibrium 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 interval $t = 0$ to $t = 4.0\,\text{s}$.
(a(ii))[2]
State, with a reason, whether the damping from time $t = 4.0\,\text{s}$ onward is light, critical or heavy.
(a(iii))[2]
Determine the natural frequency of oscillation for the magnet on the spring.
(b(i))[2]
State Faraday’s law for electromagnetic induction.
(b(ii))[4]
Explain why, after time $t = 4.0\,\text{s}$, the magnet’s vibration amplitude is observed to decrease.
Worked solution & mark scheme
This 11-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Amplitude stays constant” …