Question

The magnetic induction due to short bar magnet on its axial line at a distance 'd' is 'B'. What is the magnetic induction due to the same bar magnet on the same line at a distance $\frac{d}{4}?$

• A. 16B
• B. 32B
• C. 64B
• D. 128B

Answer 1

The correct option is C 64B

$B=\frac{{\mu }_{0}2M}{4\pi d^3}$
At $\frac{d}{4}$ distance,
$B^{\prime }=\frac{{\mu }_{0}2M}{4\pi (d/4{)}^3}$
$=\frac{{\mu }_{0}2M}{4\pi d^3}\times 64=64B$