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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: At resonance, LCR series circuit have a maximum current.
Reason: At resonance, in LCR series circuit, the current and e.m.f are in phase with each other.
✓

Answer

  1. Both A and R are true but R is not the correct explanation of A.

Explanation:

At resonance XL= XC or $\omega\text{L}=\frac{1}{\omega\text{C}}.$ Because of this impedance of LCR series circuit become equal to resistance of circuit $\Big(\text{Z}=\sqrt{\text{R}^2+(\text{X}_\text{L}-\text{X}_\text{C})^2}\Big).$ Therefore from $\text{I}=\frac{\text{E}}{\text{Z}}=\frac{\text{E}}{\text{R}},$ at resonance, current in LCR series circuit is maximum. Correspondingly phase angle is also equal to zero. Therefore emf and current are in phase in LCR series circuit.

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