Question

If a bar magnet of pole strength $m$ and magnetic moment $M$ is cut into $5$ equal parts parallel to its axis and $4$ parts equally perpendicular to its axis, then the pole strength and magnetic moment of each piece are respectively

• A. $\frac{m}{4};\frac{M}{20}$
• B. $\frac{m}{20};\frac{M}{20}$
• C. $\frac{m}{5};\frac{M}{4}$
• D. $\frac{m}{5};\frac{M}{20}$

Answer 1

The correct option is D $\frac{m}{5};\frac{M}{20}$


When a bar magnet is cut into $n$ equal parts parallel to its length and $y$ equal parts parallel to its length then,

Pole strength of each part, $m^{{}^{\prime }}=\frac{m}{x}=\frac{m}{5}$
,
Length of each part, $l^{{}^{\prime }}=\frac{2l}{y}=\frac{2l}{4}$

Magnetic moment of each part $M^{{}^{\prime }}=\frac{M}{xy}=\frac{M}{20}$

<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--> Hence, $\left(D\right)$ is the correct answer.