- A bar magnet of mass 0.12 kg is suspended from a vertical spring of spring constant 7.4 N m⁻¹. The mass of the spring is negligible.
(a) For the magnet in the equilibrium position, calculate the elastic potential energy stored in the spring. [2]
The magnet–spring system performs simple harmonic motion in the vertical direction. The spring remains stretched all the time. The diagram shows how the elastic potential energy E_p stored in the spring varies with time t during one period of oscillation.
(b) (i) State and explain the direction of motion of the magnet at t = 0.2 s. [2]
(ii) Describe the energy transfers that take place between t = 0.2 s and t = 0.4 s. [2]
(c) (i) Show that the amplitude of the oscillation of the magnet is about 0.1 m. [3]
(ii) Calculate the maximum speed of the magnet. [2]
(iii) Determine the kinetic energy of the magnet at t = 0.15 s. [2]
(Question 9 continued)
A stationary horizontal coil is placed directly below the oscillating magnet.
(d) (i) Discuss two factors that affect the magnitude of the emf induced in the coil. In your answer, you should explain:
● how an induced emf can arise in the coil, and
● how each factor affects the magnitude of the emf. [4]
(ii) A resistor is now connected across the coil. The amplitude of oscillation of the magnet rapidly decreases.
Explain this phenomenon. [3]