Q91 / 120 · VITEEE 2019 · Physics

The magnetic field at a distance $r$ from a long wire carrying current i is $0.4$ tesla. The magnetic field at a distance $2 \mathrm{r}$ is

Correct answer
A
$0.2$ tesla
B
$0.8$ tesla
C
$0.1$ tesla
D
$1.6$ tesla

Solution

Magnetic field due to long wire, $$ B=\frac{\mu_{0} i}{2 \pi r} \text { or } B \propto \frac{1}{r} $$ When $r$ is doubled, the magnetic field becomes half, i.e., now the magnetic field will be $0.2 \mathrm{~T}$.

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

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