Which component transfers energy through magnetic fields to change AC voltages?

Which component transfers energy through magnetic fields to change AC voltages?

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

Answer: (C)

Energy transfer through changing magnetic fields to change AC voltages is the job of a transformer. It uses two or more windings on a common magnetic core; when AC flows in the primary, it creates a rapidly changing magnetic flux in the core that links to the secondary winding. This changing flux induces a voltage in the secondary proportional to the turns ratio, so you can step the voltage up or down without a direct electrical connection. The energy is carried by the magnetic field, not by the wires themselves, and in an ideal case input power roughly equals output power (minus losses). This only works with AC (or a changing current) because a steady DC current would produce a constant flux after the initial transient and would not sustain energy transfer. The other components don’t fit because an open switch stops current and doesn’t transfer energy; a resistor converts electrical energy into heat without changing voltage via magnetic coupling; a thermistor is just a temperature-sensitive resistor, not a device for energy transfer through magnetic fields.

Energy transfer through changing magnetic fields to change AC voltages is the job of a transformer. It uses two or more windings on a common magnetic core; when AC flows in the primary, it creates a rapidly changing magnetic flux in the core that links to the secondary winding. This changing flux induces a voltage in the secondary proportional to the turns ratio, so you can step the voltage up or down without a direct electrical connection. The energy is carried by the magnetic field, not by the wires themselves, and in an ideal case input power roughly equals output power (minus losses). This only works with AC (or a changing current) because a steady DC current would produce a constant flux after the initial transient and would not sustain energy transfer. The other components don’t fit because an open switch stops current and doesn’t transfer energy; a resistor converts electrical energy into heat without changing voltage via magnetic coupling; a thermistor is just a temperature-sensitive resistor, not a device for energy transfer through magnetic fields.