Which device uses magnetic fields to transfer energy and adjust AC voltages?

Which device uses magnetic fields to transfer energy and adjust AC voltages?

• A. Transformer
• B. Resistor
• C. Thermistor
• D. Open Switch

Answer: (A)

Transforming and controlling AC voltages through magnetic coupling is what a transformer does. It has two windings wrapped around a magnetic core. When AC flows in the primary winding, it continually changes the current, which creates a changing magnetic flux in the core. That changing flux links to the secondary winding and induces a voltage there. The amount of voltage induced on the secondary depends on the turns ratio between the windings, so the device can step the voltage up or down while transferring energy from the input side to the output side. Because this process relies on a changing magnetic field, it only works with alternating current; with direct current, the flux would rise briefly and then stay steady, and little or no energy would be transferred. The other devices don’t fit this description: a resistor uses electric resistance to dissipate energy as heat, not magnetic coupling; a thermistor is simply a temperature-sensitive resistor; an open switch just breaks the circuit and does not transfer energy or adjust voltages through mutual induction.

Transforming and controlling AC voltages through magnetic coupling is what a transformer does. It has two windings wrapped around a magnetic core. When AC flows in the primary winding, it continually changes the current, which creates a changing magnetic flux in the core. That changing flux links to the secondary winding and induces a voltage there. The amount of voltage induced on the secondary depends on the turns ratio between the windings, so the device can step the voltage up or down while transferring energy from the input side to the output side. Because this process relies on a changing magnetic field, it only works with alternating current; with direct current, the flux would rise briefly and then stay steady, and little or no energy would be transferred.

The other devices don’t fit this description: a resistor uses electric resistance to dissipate energy as heat, not magnetic coupling; a thermistor is simply a temperature-sensitive resistor; an open switch just breaks the circuit and does not transfer energy or adjust voltages through mutual induction.