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Alternating Current — Physics STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsAlternating Current3 Marks
Question
  1. When an AC source is connected to an ideal inductor show that the average power supplied by the source over a complete cycle is zero.
  2. A lamp is connected in series with an inductor and an AC source. What happens to the brightness if the lamp when the key is plugged in and an iron rod is inserted inside the inductor? Explain.
✓

Answer

  1. $\text{P}_{av} = \text{I}_{av}\text{x }\text{ e}_{av}\cos\phi$
For an ideal inductor, $\phi = \frac{\pi}{2}$

$\therefore\text{P}_{av} = \text{l}_{av} \text{x } \text{ e}_{av}\cos\frac{\pi}{2}$

$\text{P}_{av} = 0 .$
  1. Brightness decreases:
Because as iron rod is inserted inductance increases. Thus, current decreases and brightness decreases.

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