The device used to regulate the heat in electric clothes dryers is the thermostat (specifically a cycling thermostat/temperature thermostat).

How the dryer thermostat works

  • Electric dryers have one or more thermostats placed in the air path (often near the exhaust or heater housing). These are temperature‑sensitive switches.
  • When the air inside the dryer reaches a preset temperature, the thermostat opens the circuit, cutting power to the heating element so it can cool down.
  • As the air cools, the thermostat closes again, restoring power to the heater; this on‑off cycling keeps the temperature in a safe and relatively constant range.

Other dryer parts (for context)

  • The heating element actually produces the heat, but it does not regulate it; it simply heats whenever it receives power.
  • A timer or electronic control sets how long the dryer runs and when the cycle ends, but it does not directly control temperature.
  • High‑limit thermostats or thermal fuses are safety devices that shut the dryer off if it gets dangerously hot, backing up the main cycling thermostat.

So if the question is “which of the following is used to regulate the heat in electric clothes dryers?”, the correct choice is the thermostat (cycling thermostat/temperature thermostat).