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Problem 8: A coil of pure inductance 318 mH is connected in series with a pure resistance of 75 ohms. The voltage across resistor is 150 V and the frequency of power supply is 50 Hz. Calculate the voltage of power source and the phase angle.



Inductance, L = 318 mH = 0.318 H
Resistance of resistor, R = 75 Ω
Voltage drop of resistor, VR = 150 V
Frequency of voltage, f = 50 Hz

Find: Voltage of the power source, V and phase angle ϕ.


(1) Now to find V, we know the value of VR. However, VL needs to be calculated. For this purpose, we calculate the current which passes through the series circuit and the inductive reactance, XL.

Now put the values in the formula, VL = IXL,

VL = 2 × 100 = 200 V

Now use formula (1) to find V,

To find phase angle ϕ,


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