Question

1. in rl series circuits,

a voltage leads current by 180 degrees
b current leads voltage by 180 degrees
c resistance leads current by 90 degrees
d voltage leads current by 90 degrees

Explanation:

In an RL (resistor - inductor) series circuit, the inductor causes a phase difference. The voltage across an inductor \(v = L\frac{di}{dt}\). For a sinusoidal current \(i = I_m\sin(\omega t)\), the voltage \(v = L\omega I_m\cos(\omega t)=V_m\sin(\omega t + 90^{\circ})\). So, voltage leads current by \(90^{\circ}\) in an RL series circuit.

• Option a: Incorrect. The phase difference is \(90^{\circ}\), not \(180^{\circ}\) in an RL series circuit.
• Option b: Incorrect. Current does not lead voltage in an RL series circuit.
• Option c: Incorrect. Resistance is a passive element with \(v = iR\) (in - phase relationship between \(v\) and \(i\) for a resistor), and it does not lead current by \(90^{\circ}\).
• Option d: Correct. As explained from the inductor voltage - current relationship \(v = L\frac{di}{dt}\), voltage leads current by \(90^{\circ}\) in an RL series circuit.

Answer:

D. voltage leads current by 90 degrees