Question

A horizontal overhead power line is at a height of $4m$ from the ground and carries a current of $100A$ from east to west. The magnetic field directly below it on the ground is

• A. $\text{2.5}\times {\text{10}}^{-\text{7}}T$ northwards
• B. $\text{2.5}\times {\text{10}}^{-\text{7}}T$ southwards
• C. $\text{5}\times {\text{10}}^{-\text{6}}T$ northwards
• D. $\text{5}\times {\text{10}}^{-\text{6}}T$ southwards

Answer 1

Answer: (D)

By Ampere's theorem, $B2\pi d={\mu }_{0}i$
$B=\frac{{\mu }_{0}i}{2\pi d}=\frac{4\pi \times 10^{-7}\times 100}{2\pi \times 4}$
$=$ $5\times {\text{10}}^{-\text{6}}T$ southwards