Electromagnetism
5 marks · NormalA coil of wire is moved quickly through a magnetic field in a generator, which is connected to a step-down transformer.
Describe how electromagnetic induction occurs in the coil when it is moved through the magnetic field.
Explain how changing the speed of movement of the coil affects the size of the induced voltage.
A step-down transformer connected to the generator has 3000 turns on its primary coil and 600 turns on its secondary coil. The input voltage to the primary is 240 V a.c. Calculate the output voltage of the secondary coil.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) — · must show conductor cuts magnetic field lines, voltage induced in coil
(b) Increasing speed increases the induced voltage; decreasing speed decreases it.
(c) 48 V · must show substitute transformer equation, correct calculation
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Describes the coil/conductor cutting magnetic field lines.
A1 (a) · 1 mark · States that a voltage is induced in the coil.
A2 (b) · 1 mark · Explains correctly that increasing the speed increases induced voltage (or vice versa).
M2 (c) · 1 mark · Uses the transformer equation and substitutes values correctly.
A3 (c) · 1 mark · Correct answer for output voltage (48V).
Worked solution
a) When the coil is moved through the magnetic field, the wire cuts magnetic field lines. According to electromagnetic induction, this induces a voltage in the coil.
b) The faster the coil moves, the more field lines are cut per second, so a greater voltage is induced. Slower movement leads to a smaller voltage.
Vs = (ns/np) × Vp = (600/3000) × 240 V = 0.2 × 240 V = 48 V