Question

A bar magnet of length 3 cm has points A and B along its axis at distances of 24 cm and 48 cm on the opposite sides. Ratio of magnetic fields at these points will be

• A. 8
• B. $1 / 2 \sqrt { 2 }$
• C. 3
• D. 4

Answer 1

Answer: (A)

8

Answer 2

Both points A and B lying on the axis of the magnet and on axial position

$B \propto \frac { 1 } { d ^ { 3 } }$ ⇒ $\frac { B _ { A } } { B _ { B } } = \left( \frac { d _ { B } } { d _ { A } } \right) ^ { 3 } = \left( \frac { 48 } { 24 } \right) ^ { 3 } = \frac { 8 } { 1 }$