Question

When an alternating voltage of 220V is applied across device X, a current of 0.25A flows which lags behind the applied voltage in phase by π/2 radian. If the same voltage is applied across another device Y, the same current flows but now it is in phase with the applied voltage.

1. Name the devices X and Y.
2. Calculate the current flowing in the circuit when the same voltage is applied across the series combination of X and Y.

Answer 1

(i) In device X, the Current lags behind the voltage by π/2, X is an inductor.

In device Y, Current in phase with the applied voltage, and Y is resistor.

(ii) We are given that,

Current = `"V"/"X"_"L"`

Or, `0.25 = 220/"X"_"L"`,

∴ X_L = 880Ω

Again, Current = `"V"/"R"`

Or, `0.25 = 220/"R"`

∴ R = 880Ω

For the series combination of X and Y,

Equivalent impedance Z = `sqrt(880^2 + 880^2)`

Z = `880sqrt2Omega`

Current = `"V"/"Z"`

Or, I = `220/(880sqrt2)`

∴ I = 0.177 A