For the circuit given in the figure, the voltage V C (in volts) a
![For the circuit given in the figure, the voltage V C (in volts) a](/img/relate-questions.png)
For the circuit given in the figure, the voltage VC (in volts) across the capacitor is
A. <span class="math-tex">\(1.25\sqrt 2 \sin \left( {5{\rm{t}} - 0.25{\rm{\pi }}} \right)\)</span>
B. <span class="math-tex">\(1.25\sqrt 2 \sin \left( {5{\rm{t}} - 0.125{\rm{\pi }}} \right)\)</span>
C. <strong><span class="math-tex">\(2.5\sqrt 2 \sin \left( {5{\rm{t}} - 0.25{\rm{\pi }}} \right)\)</span></strong>
D. <span class="math-tex">\(2.5\sqrt 2 \sin \left( {5{\rm{t}} - 0.125{\rm{\pi }}} \right)\)</span>
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Right Answer is: C
SOLUTION
The capacitive impedance is given by:
\(X_C=\frac{1}{ω C}\)
With ω = 5 and C = 1 μF, we can write:
\({{\rm{X}}_{\rm{C}}} = \frac{1}{{5 \times {{10}^{ - 6}}}}Ω\)
XC = 200 kΩ
The voltage across the capacitor will be:
\({{\rm{V}}_{\rm{C}}} = 5\angle 0 \times \frac{{\left( { - {\rm{j}}200} \right)}}{{200 - {\rm{j}}200}} \)
\(V_C= 5\angle 0 \times \frac{{ - {\rm{j}}\left( {1 + {\rm{j}}} \right)}}{2}\)
\(V_C= 2.5\sqrt 2 \angle - 45^\circ \)
In terms of π, the above can be written as:
\(V_C= 2.5\sqrt 2 \angle - 0.25{\rm{\pi }}\)
Converting the phasor representation back to the time domain representation, we can write:
\(\\ {{\rm{V}}_{\rm{c}}}\left( {\rm{t}} \right) = 2.5\sqrt 2 \sin \left( {5{\rm{t}} - 0.25{\rm{t}}} \right) \)