Question

A series R-C circuit is connected to an alternating voltage source. Consider two situation:
(a) When capacitor is filled
(b) When capacitor is mica filled
Current through resister is i and voltage across capacitor is V then :

• A. $V_a=V_b$
• B. $V_a<V_b$
• C. $V_a>V_b$
• D. $i_a=i_b$

Answer 1

Answer: (C)

$V_a>V_b$

For series C-R circuit, the impedance $Z=\sqrt{R^2+X_C^2}$ where $X_C=\frac{j}{\omega C}$ and current $I=V/Z$

When the capacitor is filled by mica, the capacitance will be increased. If C increases, $X_C$ decreases, so the current will increase and

hence voltage across resistance increases and voltage across capacitor decreases. thus, $V_a>V_b$