Question

Two magnets are held together in a vibration magnetometer and are allowed to oscillate in the earth's magnetic field. With like poles together 12 oscillations per minute are made but for unlike poles together only 4 oscillations per minute are executed. The ratio of their magnetic moments is

• A. 3 : 1
• B. 1 : 3
• C. 3 : 5
• D. 5 : 4

Answer 1

Answer: (D)

5 : 4

Answer 2

By using $\frac { M _ { 1 } } { M _ { 2 } } = \frac { T _ { d } ^ { 2 } + T _ { s } ^ { 2 } } { T _ { d } ^ { 2 } - T _ { s } ^ { 2 } }$ where and

$T _ { d } = \frac { 60 } { 4 } = 15 \mathrm { sec }$ $\therefore \frac { M _ { 1 } } { M _ { 2 } } = \frac { ( 15 ) ^ { 2 } + ( 5 ) ^ { 2 } } { ( 15 ) ^ { 2 } - ( 5 ) ^ { 2 } } = \frac { 5 } { 4 }$