Question

An unusual lightning strike has a vertical portion with a current of –400 A downwards. The Earth’s magnetic field at that location is parallel to the ground and has a magnitude of 30 μT. In units of N (Newtons), the force exerted by the Earth’s magnetic field on the 25 m-long current is Group of answer choices 300 A, East. 0.30 A, West. 0 0.012 A, East. 0.012 A, West.

Answer 1

Given that,

Current, I = 400 A (downwards)

The Earth’s magnetic field at that location is parallel to the ground and has a magnitude of 30 μT.

We need to find the force exerted by the Earth’s magnetic field on the 25 m-long current. We know that the magnetic force is given by :

$F=iLB\sin\theta$

Here, $\theta=90^{\circ}$

$F=400\times 25\times 30\times 10^{-6}\\\\F=0.3\ N$

The force is acting in a plane perpendicular to the current and the magnetic field i.e out of the plane.