A fan circuit's regulator has multiple resistance steps. What happens electrically when the knob is turned to a higher setting?
Circuit resistance decreases, increasing voltage at fan
A resistance-type fan regulator works as a voltage divider: it places selectable steps of series resistance between the supply and the fan motor, and the speed follows the voltage that actually reaches the motor.
Because the regulator and motor are in series, the supply voltage is shared between them in proportion to their resistances.
Turning the knob to a higher setting switches in a smaller value of series resistance, so less voltage is dropped across the regulator itself.
With that drop reduced, a larger share of the supply voltage appears across the fan motor.
The greater motor voltage drives more current through the winding, producing more torque and a higher running speed, which is why the higher setting means a faster fan.
The options claiming that resistance increases, or that the motor gets less voltage, describe the low-speed direction and so are the reverse of what happens; the fan is certainly not disconnected.
Hence, the answer is Circuit resistance decreases, increasing voltage at fan.
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