The circuit is protected by a ground fault interrupter in the plug. The water in the tank is grounded. The two bare wires correspond to the two pins on the ground fault interrupter plug. If the wire is touched to the water, the ground fault interrupter will disconnect the circuit.

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.

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