Q. The strength of the magnetic field at a point $r$ near a long straight current carrying wire is $B$. The field at a distance $\frac{r}{2}$ will be
A) $\frac{B}{2}$
B) $\frac{B}{4}$
C) $2B$
D) $4B$
Explanation
(c) $B \propto \frac{1}{r} \Rightarrow \frac{B_{1}}{B_{2}} = \frac{r_{2}}{r_{1}} \Rightarrow \frac{B}{B_{2}} = \frac{r/2}{r} \Rightarrow B_{2} = 2B$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.