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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.
- Name the devices X and Y.
- Calculate the current flowing in the circuit when the same voltage is applied across the series combination of X and Y.
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Solution
(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"`,
∴ XL = 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
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