Magnetism Question 160
Question: The distance of two points on the axis of a magnet from its centre is 10 cm and 20 cm respectively. The ratio of magnetic intensity at these points is 12.5 : 1. The length of the magnet will be
Options:
A) 5 cm
B) 25 cm
C) 10 cm
D) 20 cm
Show Answer
Answer:
Correct Answer: C
Solution:
$ \frac{B _{1}}{B _{2}}=\frac{d _{1}}{d _{2}}{{( \frac{d _{2}^{2}-l^{2}}{d _{1}^{2}-l^{2}} )}^{2}}\Rightarrow \frac{12.5}{1}=\frac{10}{20}{{( \frac{400-l^{2}}{100-l^{2}} )}^{2}} $
$ \Rightarrow l=5\ cm $ Hence length of magnet $ =2l=10\ cm $
BETA
