Physics - Current Electricity Question with Solution | TestHub

Equivalent resistance of the parallel $20\Omega$ branches will be $10\Omega$.

Equivalent EMF of the two branches which are in parallel will be, $=\frac{\frac{1.5}{r}+\frac{1.5}{r}}{\frac{1}{r}+\frac{1}{r}}=1.5\mathrm{V}$ and the equivalent internal resistance for same branches will be, $\frac{r}{2}$.

For loop containing voltmeter and $10\Omega$ resistor, $1.2-10i=0\Rightarrow i=0.12\text{A}$. Reading of voltmeter should be,

$1.2=1.5-i\left(\frac{r}{2}\right)\Rightarrow i\left(\frac{r}{2}\right)=0.3\Rightarrow r=\frac{0.6}{i}=\frac{0.6}{0.12}=5\Omega$