Final answer:
A triangular-shaped external magnetic field will induce a triangular-shaped EMF in the pickup coil, as the induced EMF is directly proportional to the rate of change of magnetic flux, and the triangular field changes at a constant rate.
Step-by-step explanation:
A student has asked about the shape of the electromotive force (EMF) that would be induced in a pickup coil when exposed to a triangular-shaped external magnetic field. According to Faraday's Law of Electromagnetic Induction, the induced voltage or EMF in a coil is directly proportional to the rate of change of magnetic flux passing through it. Since the magnetic field changes in a triangular pattern, with consistent rates of increase and decrease, this would induce a triangular-shaped EMF in the pickup coil. This is because the rate of change of the magnetic field strength is constant during the increase and decrease, which corresponds directly to the straight lines that form the triangular shape of the EMF waveform.