NEET-XII-Physics
39: Alternating Current
- #4An inductor coil of some resistance is connected to an AC source. Which of the following quantities have zero average value over a cycle?
(a) Current
(b) Induced emf in the inductor
(c) Joule heat
(d) Magnetic energy stored in the inductordigAnsr: a,bAns : (a) Current
(b) Induced emf in the inductor
For a series L-R circuit, the AC current can be given by,
`` i={i}_{0}\,\mathrm{\,sin\,}\omega t``
From the graph, we can see that the average value of current over a cycle is zero.
Since it a series L-R circuit, the phase difference between current and voltage is `` \frac{\pi }{2}``. The AC voltage can be given by,
`` V={V}_{0}\,\mathrm{\,cos\,}\omega t``
From the graph, we can see that the average value of voltage over a cycle is also zero.
Joule's heat through the resistor is given by,
`` {H}_{avg}={{i}_{rms}}^{2}R``, which is non zero.
Similarly, magnetic energy stored in the inductor is given by,
`` {U}_{avg}=\frac{1}{2}L{{i}_{rms}}^{2}`` , which is also non-zero.
Page No 330: