What symbol would best represent an electric fan in an electric circuit?

Fan is actually a Electro-magnetic motor so the symbol used for motors can also be used for a fan ( "M" written in a circle )

The symbol of a motor, a letter M inside a circle.

Explanation: A fan works with a small motor, that allows the blades to spin, and this is a simplifyed explanation of how a fan works.

So the symbol in the circuit will be the one of a motor, that is represented with a letter M inside a circle.

diagram is missing, but i will try to explain your doubt.

answer:

amplitude is the maximum displacement or distance moved on a point of a vibrating body or wave measured from its equilibrium position.it is equal to half the length of vibration path.

power out to power in less than 100%