Question

Points A and B are situated along the extended axis of 2 cm long bar magnet at a distance x and 2x cm respectively. From the pole nearer to the points, the ratio of the magnetic field at A and B will be

• A. 4 : 1 exactly
• B. 4 : 1 approx.
• C. 8 : 1 exactly
• D. 8 : 1 approx.

Answer 1

Answer: (D)

8 : 1 approx.

Answer 2

For a magnet $B = \frac { \mu _ { 0 } } { 4 \pi } \cdot \frac { 2 M } { x ^ { 3 } }$ (Nearly)

$\Rightarrow \frac { B _ { 1 } } { B _ { 2 } } = \left( \frac { x _ { 1 } } { x _ { 2 } } \right) ^ { 3 } = \left( \frac { x } { 2 x } \right) ^ { 3 } = \frac { 1 } { 8 }$ (Approx.)