Question

The geometric length of a bar magnet of pole strength 80 A.m. and magnetic moment 4 amp m${}^2$ :

• A. 6 cm
• B. 5 cm
• C. $\frac{5}{6}$cm
• D. $\frac{6}{5}$cm

Answer 1

The correct option is A 6 cm

Pole strength$=m=80Am$

Magnetic moment$=M=4A{m}^2$

let magnetic length$=l_m$

geometric length$=l_g$

But,

$M=m.l_m$

$\therefore 4=80\times l_m$

$\therefore l_m=4/80=0.05m=5cm$

But,

$l_m=\frac{5}{6}{l}_g$

$\therefore 5=\frac{5}{6}{l}_g$

$\therefore$ Geometric length $=l_g=6cm$