Magnetism Question 232
Question: Force between two identical bar magnets whose centres are r metre apart is 4.8 N, when their axes are in the same line. If separation is increased to r, the force between them is
Options:
A) 2.4 N
B) 1.2N
C) 0.6 N
D) 0.3 N
Show Answer
Answer:
Correct Answer: D
Solution:
[d] Force between two short bar magnets is given by $ F,,,,,=,,,,\frac{{\mu _{0}}}{4\pi }\frac{6M _{1}M _{2}}{r^{4}} $
$ \
Therefore ,,,,,,\frac{F _{1}}{F _{2}}=\frac{r _{2}^{4}}{r _{1}^{4}}={{( \frac{2r}{r} )}^{4}} $ or $ F _{2}=\frac{F _{1}}{16}=\frac{4.8}{16}=0.3,N $ .
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