Question

An alternating voltage of 220 V is applied across a device X. A current of 0.22 A flows in the circuit and it lags behind the applied voltage in phase by π/2 radian. When the same voltage is applied across another device Y, the current in the circuit remains the same and it is in phase with the applied voltage.

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

Answer 1

1. X is a resistor and Y is the capacitor.
2. 
    
   R = `V_{rms}/I_{rms} = 220/0.22 = 1000 Omega`
   R = X_C = 1000Ω
   When R and C are in series.
   `I_{rms} = V_{rms}/Z = V_{rms}/sqrt(R^2 + (X_C)^2)`
   = `220/sqrt((1000)^2 + (1000)^2)`
   = `220/(1000 xx sqrt2)`
   `I_{rms} = 0.156` A