Question

When two magnetic poles having same pole strength are separated by a distance of $20$ $cm$, a force of $5$ $N$ acts between them. If the distance is halved, the force becomes ______

• A. $20$ N
• B. $10$ N
• C. $15$ N
• D. $25$ N

Answer 1

The correct option is B $10$ N

When two magnetic poles having same pole strength are separated by a distance

$\frac{F}{l}=\frac{{\mu }_0{I}_1{I}_2}{2\pi r}$

$\frac{5}{l}=\frac{K{I}_1{I}_2}{0.20}$

$\frac{5\ast 20}{100l}=K{I}_1{I}_2$

$K{I}_1{I}_2=1$

when distance is half

$\frac{F}{l}=\frac{K{I}_1{I}_2}{r/2}$

$\frac{F}{l}=\frac{1}{\left(0.10\right)}$

$\frac{F}{l}=10N$