Question

A magnetic needle suspended by a silk thread is oscillating in the earth’s magnetic field. If the temperature of the needle is increased by ${500}^{o}C$ then :

• A. the time period decreases
• B. the time period increases
• C. the time period remain unchanged
• D. the needle stops vibrating

Answer 1

The correct option is B the time period increases

The time period of oscillation of a bar magnet freely suspended in air is given by $T=2\pi \sqrt{\frac{I}{M{B}_H}}$

When the magnet is heated above ${500}^{o}C$ , the magnet loses its pole strength and thus decreases the magnetic moment. Time period of oscillation is inversely proportional to the magnetic moment . So, the time period increases.