Magnetism Question 273
Question: A freely suspended magnet oscillates with period T in earth’s horizontal magnetic field. When a bar magnet is brought near it, such that the magnetic field created by bar magnet is in same direction as earth’s horizontal magnetic field, the period decreases to T/2. The ratio of the field of the magnet F to the earth’s magnetic field (H) is
Options:
A) 1 : 3
B) 1 : 1
C) 3 : 1
D) 9 : 1
Show Answer
Answer:
Correct Answer: C
Solution:
[c] $ T _{1}=2\pi \sqrt{\frac{I}{HM}} $ , and $ T _{2}=2\pi \sqrt{\frac{I}{(H+F)M}} $
$ \frac{T _{1}^{2}}{T _{2}^{2}}=\frac{H+F}{H}=\frac{T^{2}}{T^{2}/4}=\frac{4}{1}\Rightarrow H+F=4H $
$ \Rightarrow ,,3H=F $
BETA
