Question

A current in a wire increases from 2 A to 6 A. How will the magnetic field 0.01 m from the wire change?

It increases to four times its original value.
It increases to three times its original value.
It decreases to one-fourth its original value.
It decreases to one-third its original value.

Answer 1

B ∝ I for a long straight wire (B = μ0 I / 2πr). If I goes from 2 A to 6 A, B multiplies by 6/2 = 3.

So it increases to three times its original value.