Question

Find the current through the resistance $R$ in figure if $R=12\Omega$.

• A. $0.21\text{A}$
• B. $0.42\text{A}$
• C. $0$
• D. $0.6\text{A}$

Answer 1

The correct option is B $0.42\text{A}$


When $R=12\Omega$, the effective emf and resistance of the branch $\text{AB}$ and $\text{CD}$ are given by,

$\frac{E_{eff}}{r_{eff}}=\frac{E_1}{r_1}-\frac{E_2}{r_2}$

Here, $r_{eff}=\frac{12\Omega }{2}=6\Omega$

$\Rightarrow \frac{E_{eff}}{6}=\frac{6}{12}-\frac{4}{12}$

$E_{eff}=1\text{V}$

So, the given circuit can be reduced to

As the diode is reverse biased, the branch $\text{EF}$ becomes ineffective.

Now, using Kirchhoff's voltage on the loop $\text{ABCDA}$,

The current $i$ through the resistance $R$ will be

$i(12+12)=6+4$

$i=\frac{10}{24}=0.4166=0.42\text{A}$

Hence, option $\left(\text{B}\right)$ is correct.