A) 20 W
B) 40 W
C) 1000 W
D) zero
Correct Answer: D
Solution :
Key Idea: Power dissipated depends upon phase difference between current and voltage in AC circuit. The rate of dissipation of energy in an electrical circuit is called the power. It is given by \[P={{E}_{rms}}\times {{i}_{rms}}\times \cos \text{o }\!\!|\!\!\text{ }\] where \[{{\text{E}}_{\text{rms}}}\] is the root mean square value of potential difference and \[{{\text{i}}_{rms}}\] is the root mean square value of current and \[\text{o }\!\!|\!\!\text{ }\] in phase difference. Given, \[\text{o }\!\!|\!\!\text{ =}\frac{\pi }{2}\] \[\therefore \] \[\cos \text{o }\!\!|\!\!\text{ =0}\] \[\therefore \] \[P={{E}_{rms}}\times {{i}_{rms}}\times 0=0\] Note: The average power dissipated in the circuit is zero, that is there is no energy dissipation in the circuit hence current in such a circuit is called wattless current. In practice however, a wattless current is not a reality because no circuit can be entirely resistanceless.
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