Question

The distance between two magnetic poles is doubled and their pole-strength is also doubled. The force between them

• A. Increases to four times
• B. Decreases by half
• C. Remains unchanged
• D. Increases to two times

Answer 1

Answer: (C)

Remains unchanged

The force between two magnetic poles is directly proportional to the product of their strengths and is inversely proportional to the square of the distance between them.

Hence the new force $F_2$ will be given by

$\frac{F_2}{F_1}=\frac{\left(\frac{m_{A2}\times m_{B2}}{{d_2}^2}\right)}{\left(\frac{m_{A1}\times m_{B1}}{{d_1}^2}\right)}=\frac{\left(\frac{2m_{A1}\times 2m_{B1}}{{4d_1}^2}\right)}{\left(\frac{m_{A1}\times m_{B1}}{{d_1}^2}\right)}$

$\therefore F_1=F_2$