question_answer

Directions: In the following questions, a statement of Assertion [A] is followed by a statement of Reason (R).

Mark the correct choice as:

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 lags behind potential difference across the inductance by an angle \[\pi /2\].

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 [A] and Reason (R) are true and Reason (R) is the correct explanation of Assertion [A]        

B) Both Assertion [A] and Reason (R) are true but Reason (R) is not the correct explanation of Assertion [A]

C) Assertion [A] is true but Reason (R) is false

D) Assertion [A] is false and Reason (R) is also false

Correct Answer: B

Solution :

(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. While in case of an inductance when current is zero, potential difference across it is maximum and when current reaches maximum (at \[\omega t=\pi /2\]). potential difference across it becomes zero i. e., potential difference leads the current by \[\pi /2\] or current lags behind the potential difference by \[\pi /2\]. Phase angle in case of LR  circuit is given as \[\phi ={{\tan }^{-1}}\left( \frac{\omega L}{R} \right)\].