Question

what symbol would best represent an electric fan speed controller in an electric circuit?

Explanation:

1. Analyze each symbol:

• The first symbol (switch) is for opening/closing a circuit, not for speed control.
• The second symbol (light bulb) represents a load that emits light, not a speed controller.
• The third symbol (resistor, often a variable resistor can be used for speed control as it changes resistance to adjust current, which in turn adjusts fan speed) is a resistor (or variable resistor) symbol.
• The fourth symbol (battery) is a power source, not a speed controller.

Answer:

The symbol with the zig - zag line (the resistor - like symbol, the third one in the options).