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Alternating Current — Physics STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 SciencePhysicsAlternating Current1 Mark
MCQ
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
    Va​ = Vb​
  • B
    Va​ < Vb​
  • C
    Va​ > Vb​
  • D
    ia​ = ib​
✓

Answer

  1. Va​ > Vb​

Explanation:

For series C - R circuit, the impedance $\text{Z}=\sqrt{\text{R}^2+\text{X}^2_\text{C}}$ where $\text{X}_\text{C}=\frac{\text{i}}{\omega\text{C}}$ and current $\text{I}=\frac{\text{V}}{\text{Z}}$

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

hence voltage across resistance increases and voltage across capacitor decreases. thus, Va​ > Vb​

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