A long, East-West-oriented power cable carrying an unknown current I is at a height of 8 m above the Earth's
surface. If the magnetic flux density recorded by a magnetic-
field meter placed at the surface is 15 ut when the current is
flowing through the cable and 20 ut when the current is zero,
what is the magnitude of 1?

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

i think it’s a. this is because if they measured the mass of something with a mass of 150g, then their final answer would have to be approximately 150g. though all of their answers are almost 150, rosa and tran have the closest answers (or the exact answer) to the accurate one.

the answer is b

explanation: