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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: An inductance and a resistance are connected in series with an A.C. circuit. ln this circuit the current and the potential difference across the resistance lags behind potential difference across the inductance by an angle $\frac{\pi}{2}.$
Reason: In L-R circuit voltage leads the current by phase angle which depends on the value ofinductance and resistance both.
✓

Answer

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

Explanation:

As both the inductance and resistance are joined in series, hence current through both will be same. But in case of resistance, both the current and potential vary simultaneously, hence they are in same phase. While in case of an inductance when current is zero, potential difference across it is maximum and when current reaches maximum $\big($at $\omega\text{t}=\frac{\pi}{2}\big),$ potential difference across it becomes zero i.e., potential difference leads the current by $\frac{\pi}{2}$ or current lags behind the potential difference by $\frac{\pi}{2}.$ Phase angle in case of LR circuit is given as $\phi=\tan^{-1}\Big(\frac{\omega\text{L}}{\text{R}}\Big).$

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