Q138 / 180 · COMEDK 2013 · Physics

In the circuit shown, the internal resistance of the cell is negligible. The steady state current in the $2 ~\Omega$ resistor is
Figure

  • A
    $0.6 \mathrm{~A}$
  • B
    $1.2 \mathrm{~A}$
  • Correct answer
    C
    $0.9 \mathrm{~A}$
  • D
    $1.5 \mathrm{~A}$

Solution

$2 \Omega$ and $3 \Omega$ resistors are in parallel, so their equivalent resistance, $$ R_{\text {eq }}=\frac{2 \times 3}{2+3}=\frac{6}{5}=1.2 \Omega $$ As capacitor blocks DC at steady state, so the resistor $4 \Omega$ is ineffective. The $R_{\text {eq }}$ and $28 \Omega$ are in series, so total resistance of circuit, $$ R_{T}=1.2+2.8=4 \Omega $$ Current in circuit, $I=\frac{V}{R_{T}}=\frac{6}{4}=15 \mathrm{~A}$ Potential across the combination of $2 \Omega$ and $3 \Omega$ resistors $\quad V^{\prime}=15 \times 1.2=1.8 \mathrm{~V}$ $\therefore$ The steady state current in $2 \Omega$ resistor is $$ I^{\prime}=\frac{V^{\prime}}{2}=\frac{1.8}{2}=0.9 \mathrm{~A} $$

Hence, the correct answer is option: 'C'.

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