The primary winding of a transformer has 400 turns and its secondary has 100 turns. If a source of e.m.f. of 12V is applied to the primary, the secondary e....

Answer Details

The ratio of the number of turns in the primary winding to the number of turns in the secondary winding of a transformer is called the turns ratio. In this case, the turns ratio is 400:100, or 4:1. When a voltage is applied to the primary winding of a transformer, it creates a changing magnetic field which induces a voltage in the secondary winding. The magnitude of the induced voltage depends on the turns ratio. To calculate the secondary voltage in this transformer, we can use the turns ratio and the voltage applied to the primary. Since the turns ratio is 4:1, the secondary voltage will be one-fourth the primary voltage. Therefore, the secondary voltage in this transformer will be 12V divided by 4, which is equal to 3V. So the correct answer is option A: 3V.