Question

Points A and B are situated perpendicular to the axis of a 2cm long bar magnet at large distances X and 3X from its centre on opposite sides. The ratio of the magnetic fields at A and B will be approximately equal to

• A. 1 : 9
• B. 2 : 9
• C. 27 : 1
• D. 9 : 1

Answer 1

Answer: (C)

27 : 1

Answer 2

$B \propto \frac { 1 } { x ^ { 3 } } \Rightarrow \frac { B _ { 1 } } { B _ { 2 } } = \left( \frac { x _ { 2 } } { x _ { 1 } } \right) ^ { 3 } = \left( \frac { 3 x } { x } \right) ^ { 3 } = \frac { 27 } { 1 }$