Electromagnetic induction：练习题

Which of the following changes would not increase the maximum voltage induced in a coil of wire when a magnet is moved into it?

Why must a transformer be supplied with an alternating current (a.c.) to function?

In an a.c. generator, a coil is rotated at a constant speed in a uniform magnetic field. At which position is the magnitude of the induced voltage at its maximum?

Which of the following actions will not induce a voltage in a coil of wire?

A student rotates a magnet inside a coil of wire connected to a sensitive voltmeter. Which of the following describes the type of voltage produced?

Describe two specific modifications to a setup involving a magnet and a coil that would increase the magnitude of the induced voltage when the magnet is moved.

Explain the role of a step-up transformer in the large-scale transmission of electricity from power stations to consumers.

A transformer has a primary voltage of \(230 \text{ V}\) and a secondary voltage of \(10 \text{ V}\). If the secondary coil has \(40\) turns, calculate the number of turns on the primary coil.

A transformer is designed to step down a mains voltage of \( 230 \text{ V} \) to \( 11.5 \text{ V} \) to power a lamp. The primary coil has \( 800 \text{ turns} \).

(a) Calculate the number of turns required on the secondary coil.
(b) The lamp has a power rating of \( 23 \text{ W} \). Assuming the transformer is \( 100\% \) efficient, calculate:
i) The current flowing through the lamp.
ii) The current in the primary coil.
(c) Explain why the core of the transformer is made of a soft magnetic material like iron rather than a hard magnetic material like steel.