First slide

Magnetism

Question

A bar magnets of length 1 cm has point A & B along its axis at distances of 12 cm & 24 cm on the opposite sides. Ratio of magnetic fields at these points will be:

Moderate

A

8
B

$\frac{1}{2 \sqrt{2}}$
C

3
D

4

Solution

For a short bar magnet at a point along its axial point, $B= \frac{μ_{0}}{4π} . \frac{2M}{r^{3}}$
$∴ \frac{B_{1}}{B_{2}} = {(\frac{r_{2}}{r_{1}})}^{3} = {(\frac{24}{12})}^{3} = 2^{3} = 8$ .

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