Question

The length of a magnet is $16cm$. Its pole strength is $250mA-m$ When it is cut into four equal pieces parallel to its axis, the magnetic length, pole strength and moments of each piece are :

• A. $4cm$; $62.5mA-m$; $250mA-c{m}^2$
• B. $8cm$ ; $500mA-m$; $400mA-c{m}^2$
• C. $16cm$; $250mA-m$; $4000mA-c{m}^2$
• D. $16cm$; $62.5mA-m$; $0.01A{m}^2$

Answer 1

Answer: (D)

$16cm$; $62.5mA-m$; $0.01A{m}^2$

On cutting the magnet parallel to its axis, the magnetic length remains same.
Pole strength decreases by a factor of $4$ as it is divided into four parts
$m_{final}=250/4=62.5mA-m.$
$M_{final}=mL=16\times {10}^{-2}\times 62.5\times {10}^{-3}=0.01A{m}^2$