A student investigates a series circuit in the laboratory
PHYSICS · Multi-part · CBSE · Physics · Alternating Current · Alternating Current
Problem
A student investigates a series R−L circuit in the laboratory. During the experiment the effective (r.m.s.) supply voltage V and current I are measured with ordinary multimeters, while the resistance R of the coil is obtained by a separate d.c. measurement.
Answer the following questions based on this situation.
(i) Draw the impedance (phasor) triangle for a series R−L circuit and clearly label its sides and included angle ϕ.
(ii) Show, by using the geometrical relations of the triangle, how the inductance L of the coil can be expressed solely in terms of the measured quantities V, I, R and the supply frequency f.
(iii) Explain why the current in such a circuit always lags behind the supply voltage and identify the physical quantity that determines the magnitude of this lag.
(iv) State any two practical precautions that should be taken while performing this measurement in the school laboratory.