10 A current is flowing in two straight parallel wires in the same direction. Force of attraction between…
10 A current is flowing in two straight parallel wires in the same direction. Force of attraction between them is $1 \times 10^{-3} \mathrm{~N}$. If the current is doubled in both the wires the force will be
$1 \times 10^{-3} \mathrm{~N}$
$2 \times 10^{-3} \mathrm{~N}$
$4 \times 10^{-3} \mathrm{~N}$
$0.25 \times 10^{-3} \mathrm{~N}$
Solution
$\mathrm{F}=\frac{\mu_0}{4 \pi} \frac{2 \mathrm{I}_1 \mathrm{I}_2}{\mathrm{r}} l=10^{-3} \mathrm{~N}$
When current in both the wires is doubled, then
$\mathrm{F}^{\prime}=\frac{\mu_0}{4 \pi} \frac{2\left(2 \mathrm{I}_1 \times 2 \mathrm{I}_2\right)}{\mathrm{r}} j=4 \times 10^{-3} \mathrm{~N}$