Q151 / 160 · AP EAMCET 2011 · Physics

If a bar magnet of pole strength $m$ and magnetic moment $M$ is cut equally 5 times parallel to its axis and again 3 times perpendicular to its axis, then the pole strength and magnetic moment of each piece are respectively

  • A
    $\frac{m}{20}, \frac{M}{4}$
  • B
    $\frac{m}{5}, \frac{M}{20}$
  • Correct answer
    C
    $\frac{m}{6}, \frac{M}{24}$
  • D
    $\frac{m}{5}, \frac{M}{24}$

Solution

Given, pole strength $=m$ and magnetic moment $=M$ When it is cut 5 times parallel to its axis, pole strength, $m^{\prime}=\frac{m}{6}$ When it is cut 3 times perpendicular to its axis, then length $2 l^{\prime}=\frac{2 l}{4}$ $\therefore$ pole strength, $m^{\prime}=\frac{m}{6}$ and magnetic moment, $M^{\prime}=\left(\frac{m}{6}\right)\left(\frac{2 l}{4}\right)=\frac{M}{24}$

Hence, the correct answer is option: 'C'.

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