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Alternating Current — Physics STD 12 Science — Question

Gujarat 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: When capacitive reactance is smaller than the inductive reactance in LCR series circuit, e.m.f. leads the current.
Reason: The phase angle is the angle between the alternating e.m.f. and alternating current of the circuit.
✓

Answer

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

Explanation:

The phase angle for the LCR series circuit is given by $\tan\theta=\frac{\text{X}_\text{L}-\text{X}_\text{C}}{\text{R}}=\frac{\frac{\omega\text{L-1}}{\omega\text{C}}}{\text{R}}.$ Where XL, XC are inductive reactance and capacitive reactance respectively. When XL > XC then $\tan\theta$ is positive i.e. $\theta$ is positive $\big($between 0 and $\frac{\pi}{2}\big).$ Hence emf leads the current.

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