What device changes the voltage of alternating current?

• A. Diode
• B. Capacitor
• C. Transformer
• D. Resistor

Answer: (C)

Transformers change the voltage of alternating current by using electromagnetic induction between two windings wrapped around a magnetic core. When AC flows in the primary winding, it creates a changing magnetic flux in the core, which induces a voltage in the secondary winding. The voltages relate to the turns ratio, so the device can step voltage up or down as needed. This is how power adapters and mains transformers adjust voltage levels for different applications.

A diode, while it can rectify AC to pulsating DC, does not transform AC voltage. A capacitor stores and releases energy to smooth or couple signals but doesn’t set the overall voltage level of an AC source. A resistor simply dissipates power and drops voltage according to Ohm’s law based on the load; it doesn’t actively transform voltage.