Question

A long straight wire is carrying a current of $ 12\,A $. The magnetic field at a distance of $ 8\,cm$ is $ (\mu _{0}=4\pi \times 10^{-7}\,N/A^{2}) $

• A. $ 2\times 10^{-4}Wb/m^{2}$
• B. $ 3\times 10^{-5}Wb/m^{2}$
• C. $ 4\times 10^{-4}Wb/m^{2}$
• D. $ 4\times 10^{-5} Wb/m^{2}$

Answer 1

Answer: (B)

Magnetic field $B=\frac{\mu_{0} I}{2 \pi r}$
Given. $\mu=4 \pi \times 10^{-7} N / A^{2}$,
$r=8\, cm =8 \times 10^{-2} m$
$I=12\, A$
$B=\frac{4 \pi \times 10^{-7}}{2 \pi} \times \frac{12}{8 \times 10^{-2}}$
$\Rightarrow B=3 \times 10^{-5} Wb / m ^{2}$