Answer:
200A
Explanation:
Given that
the distance between earth surface and power cable d = 8m
when the current is flowing through cable , the magnitude flux density at the surface is 15μT
when the current flow throught is zero the magnitude flux density at the surface is 20μT
The change in flux density due to the current flowing in the power cable is
B = 20μT - 15μT
B =5μT -----(1)
The expression of magnitude flux density produced by the current carrying cable is
-----(2)
Substitute the value of flux density
B from eqn 1 and eqn 2

Therefore, the magnitude of current I is 200A
The strength, and possibly the shape and direction, of the electric field
around a charged particle depends on the location of the particle.
If the process of measuring the field causes the particle to move, then
the measurement you get wouldn't mean anything.
Your measurements wouldn't show the ACTUAL field around the particle.
They would show what the field is like AFTER something comes along
and distorts it, and that's not what you're trying to measure.
It would be like carrying a flame thrower into a freezer when you go in
to measure the temperature in there.
Or if you had to measure how much light is leaking into a dark room,
and you carried a flashlight with you to see your way around in there.