Answer to Question 2

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How does the power vary with time if a current of Irms passes through a heater with a voltage of Vrms?  Think about the power when V and I are positive and when V and I are negative.

The power is peak power when V and I are at positive peak values.

When V and I are zero, P = 0.

Positive peak power when V and I are at negative peak values

Because - - = +

 Power peaks at double the frequency of the supply.