Question

A short bar magnet produces a field of induction $160\times {10}^{-6}T$ at certain point on the axial line. The induction field strength on the same line at a point twice the distance of the first is

• A. $20\times {10}^{-5}T$
• B. $2\times {10}^{-5}T$
• C. $20\times {10}^{-4}T$
• D. $2\times {10}^{-7}T$

Answer 1

Answer: (B)

$2\times {10}^{-5}T$

$B=160\times {10}^{-6}T$
$Barial=\frac{2{\mu }_{o}m}{4\pi d^3}$
$Barial\propto \frac{1}{d^3}$
$B_1{d}_3^1=B_2{d}_2^3$
$160\times {10}^{-6}=B_2\times 2^3$
$B_2=2\times {10}^{-5}T$