A horizontal overhead power line is at a height of 4 ~m from the ground and carries a current of 100 ~A from east to west. The magnetic field directly below it on the ground is (μ_0=4 π × 10^-7 ~T ~m ~A^-1 )

Correct answer: (C) 5 × 10^-6 T southward. B=(μ_0)/(2 π) i/R=frac4 π × 10^-72 π × 100/4=5 × 10^-6 ~T southward

Q102 / 105 · JEE Main 2008 · Physics

A horizontal overhead power line is at a height of $4 \mathrm{~m}$ from the ground and carries a current of $100 \mathrm{~A}$ from east to west. The magnetic field directly below it on the ground is $\left(\mu_0=4 \pi \times 10^{-7} \mathrm{~T} \mathrm{~m} \mathrm{~A}^{-1}\right)$

$$ B=\frac{\mu_0}{2 \pi} \frac{i}{R}=\frac{4 \pi \times 10^{-7}}{2 \pi} \times \frac{100}{4}=5 \times 10^{-6} \mathrm{~T} \text { southward } $$

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