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

The correct option is D 8 : 1 approx

For a magnet $B=\frac{{\mu }_0}{4\pi }.\frac{2M}{x^3}$ (Nearly)
$\Rightarrow \frac{B_1}{B_2}={\left(\frac{x_1}{x_2}\right)}^3={\left(\frac{x}{2x}\right)}^3=\frac{1}{8}$ (Approx)