Question

Assertion (A) An inductance and a resistance are connected in series with an AC circuit. In this circuit, the current and the potential difference across the resistance logs behind potential difference across the inductance by an angle $\frac{\pi}{2}$.
Reason (R) In L-R circuit, voltage leads the current by phase angle which depends on the value of inductance and resistance both.

• A. Both assertion and reason are true and reason is the correct explanation of assertion
• B. Both assertion and reason are true but reason is not the correct explanation of assertion
• C. Assertion is true but reason is false
• D. Both assertion and reason are false

Answer 1

Answer: (B)

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. In case of an inductance when current is zero, potential difference across it is maximum and when current reaches maximum (at $\omega t=\frac{\pi}{2}$ ), 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 $L-R$ circuit is given as $\phi=\tan ^{-1}\left(\frac{\omega L}{R}\right)$.