Question

For a long straight wire, if the current is halved and the distance from the wire is doubled, what will B be then?

Answer 1

Magnetic induction of infinite forward current at point 1

$B_1=\frac{\mu \cdot \mu_0 \cdot I_1}{2\pi \cdot R_1}$

Magnetic induction of infinite forward current at point 2

$B_2=\frac{\mu \cdot \mu_0 \cdot I_2}{2\pi \cdot R_2}=\frac{\mu \cdot \mu_0 \cdot\frac{1}{2}\cdot I_1}{2\pi \cdot 2\cdot R_1}=\frac{1}{4}\cdot\frac{\mu \cdot \mu_0 \cdot I_1}{2\pi \cdot R_1}=\frac{1}{4}\cdot B_1$

Magnetic induction will decrease by 4 times.