Transformer
<u>Explanation:</u>
A transformer is a device with two or more magnetically coupled windings. A time varying current in one coil (primary winding) generates a magnetic field which induces a voltage in the other coil (secondary winding). Transformers are capable of either increasing or decreasing the voltage and current levels of their supply, without modifying its frequency, or the amount of electrical power being transferred from one winding to another via the magnetic circuit. There are two types of transformer:
1. Step up transformer - increases voltage
2. Step down transformer - decreases voltage
To protect a material from the influence of an external magnetic field, the material should be kept in soft iron ring.
So the correct answer is A.
Hope this helps,
Davinia.
