Question

A current of $6A$ flows in the circuit shown.​ What is the voltage across $R_1$ ?​

• A. $6V$
• B. $9V$
• C. $18V$
• D. $3V$

Answer 1

The correct option is B $9V$

Current will distribute equally in the 2 resistors, as they are identical.​
So, current through each resistor, $I^{{}^{\prime }}=\frac{6}{2}=3A$​
Using Ohm’s Law,
$V=I^{{}^{\prime }}R$
$V=3A\times 3\Omega =9V$​

Alternative solution:​
Finding equivalent resistance,​
$\frac{1}{R_{\text{eq}}}=\frac{1}{R_1}+\frac{1}{R_2}$
$\frac{1}{R_{\text{eq}}}=\frac{1}{3}+\frac{1}{3}$
$R_{\text{eq}}=\frac{3}{2}=1.5\Omega$
Using ohm’s law,​
$V=I{R}_{\text{eq}}$
$V=6A\times 1.5\Omega =9V$
The same potential difference will appear across each resistor as they are in parallel.​