Q. 6 5.0( 3 Votes )

(a) An alternating voltage E = Eo sinωt is applied to a circuit containing a resistor R connected in series with a black box. The current in the circuit is found to be I = Io sin (ωt + π/4).

(i) State whether the element in the black box is a capacitor or inductor.

(ii) Draw the corresponding phasor diagram and find the impedance in terms of R.

Answer :

(i) Given that E = E0Sin(ωt)

I = I0Sin(ωt + π/4)

It can be seen from the above two equations that phase angle of current at any point is greater than that of voltage by an amount of π/4. This means current leads the voltage in the circuit. This happens in a capacitive circuit. Therefore the element in the black box is a capacitor.


Vc = VR

Xc = R

Impedance Z =

Z = R√2

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