The force between two short bar magnets with magnetic moments M1 and M2 whose centres are r metre apart is 0.8 N when their axes are in the same line. If the separation is increased to 2 r, then force between them is reduced to

Question

The force between two short bar magnets with magnetic moments M1 and M2 whose centres are r metre apart is 0.8 N when their axes are in the same line. If the separation is increased to 2 r, then force between them is reduced to (A) 4.0 N (B) 2.0 N (C) 1.0 N (D) 0.5 N

Tardigrade Admin · Accepted Answer

F=(μ0/4 π) ⋅ (6 M1 M2/r4) i.e., propto (1/r4) ∴ F'=(F/16)=(8/16)=0.5 N

Q. The force between two short bar magnets with magnetic moments $M_{1}$ and $M_{2}$ whose centres are $r$ metre apart is $0.8 N$ when their axes are in the same line. If the separation is increased to $2 r$ , then force between them is reduced to

$4.0 N$

$2.0 N$

$1.0 N$

$0.5 N$

$F = \frac{μ _{0}}{4 π} \cdot \frac{6 M _{1} M _{2}}{r ^{4}}$
i.e., $\propto \frac{1}{r ^{4}}$
$∴ F^{'} = \frac{F}{16} = \frac{8}{16} = 0.5 N$

Q. The force between two short bar magnets with magnetic moments M1​ and M2​ whose centres are r metre apart is 0.8N when their axes are in the same line. If the separation is increased to 2r, then force between them is reduced to

4.0N

2.0N

1.0N

0.5N