Magnetism Question 79
Question: At a certain place a magnet makes 30 oscillations per minute. At another place where the magnetic field is double, its time period will be
[MP PMT 1989; MP PET/PMT 1988]
Options:
A) 4 sec
B) 2 sec
C) $ \frac{1}{2}\sec $
D) $ \sqrt{2}\sec $
Show Answer
Answer:
Correct Answer: D
Solution:
$ T=2\pi \sqrt{\frac{I}{MB _{H}}};\ \
Therefore \frac{T_1}{T_2}=\sqrt{\frac{(B_H)_2}{(B_H)_1}}\Rightarrow T_2=T_1\sqrt{\frac{(B_H)_1}{(B_H)_2}} $ Here n1=30 oscillation /min $ =\frac{1}{2} $ oscillation/sec
$ \
Therefore \ \frac{\mu }{4\pi }.\frac{m^{2}}{r^{2}}=50gm-wt $
$ \
Therefore T _{2}=2\sqrt{\frac{B _{H}}{2B _{H}}}=2\times \frac{1}{\sqrt{2}}=\sqrt{2}\sec $
BETA
