Question

An inductance and resistance are connected in series with an A.C circuit. In this circuit

• A. the current and P.d. across the resistance lead P.d across the inductance by $\frac{\pi }{2}$
• B. the current and P.d across the resistance lags behind the P.d. across the inductance by angle $\frac{\pi }{2}$
• C. The current across resistance leads and the P.d across resistance lags behind the P.d across the inductance by $\frac{\pi }{2}$
• D. the current across resistance lags behind and the P.d across the resistance leads the P.d across the inductance by $\frac{\pi }{2}$

Answer 1

The correct option is B the current and P.d across the resistance lags behind the P.d. across the inductance by angle $\frac{\pi }{2}$

This is very fundamental. If we apply separate voltages across resistance and inductor, then in resistance, current and voltage both are in same phase whereas in inductor, current across it lags p.d across it by $\pi /2$.
Now, when we apply voltage across inductor and resistance connencted in series then current through both of them will be same because of KCL. therefore voltage across resistor will be in same phase with current whereas voltage across inductor will lead the current across it by $\pi /2$. therefore current and voltage across resistor lags voltage across inductor by $\pi /2$.