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Alternating Current — Physics STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 SciencePhysicsAlternating Current1 Mark
Question
For two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
  1. Both A and R are true and R is the correct explanation of A.
  2. Both A and R are true but R is not the correct explanation of A.
  3. A is true but R is false.
  4. A is false and R is also false.
Assertion: The alternating current lags behind the e.m.f. by a phase angle of $\frac{\pi}{2}$ when A.C. flows through an inductor.
Reason: The inductive reactance increases as the frequency of A. C. source decreases.
✓

Answer

  1. A is true but R is false.

Explanation:

When pure inductor is connected to source of an alternating emf, then instantaneous value of alternating emf is given by $\text{E}=\text{E}_0\sin\omega\text{t},$ and corresponding alternating current is given by $\text{I}=\text{I}_0\sin(\omega\text{t}-\frac{\pi}{2}).$ From these two equations, it follows that alternating current lags behind e.m.f. by a phase angle of $\frac{\pi}{2}.$ The inductive reactance, so when frequency increases correspondingly inductive reactance also increases.

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