Force between two identical bar magnets whose Centres r meter apart is 4.8 N when their axis are in the same line. If the separation is increased to 2r meter, the force between them is reduced to:

Question

Force between two identical bar magnets whose Centres r meter apart is 4.8 N when their axis are in the same line. If the separation is increased to 2r meter, the force between them is reduced to: (A) 0.3 N (B) 0.6 N (C) 2.4 N (D) 1.2 N

Tardigrade Admin · Accepted Answer

Force between two magnets is given by <img class="img-fluid question-image" alt="image" src="https://cdn.tardigrade.in/img/question/physics/75f0e0bb4a3c5cfbdd2e5b4f01c503e8-.png" /> F=(μ0/4 π)((6 M1 M2/r4)) ⇒ F propto (1/r4) ∴ (F1/F2)=((r2/r1))4 (4.8/F2)=((2 r/r))4=16 ⇒ F2=0.3 N

Q. Force between two identical bar magnets whose Centres $r$ meter apart is $4.8 N$ when their axis are in the same line. If the separation is increased to $2 r$ meter, the force between them is reduced to:

0.3 N

0.6 N

2.4 N

1.2 N

Force between two magnets is given by

$F = \frac{μ _{0}}{4 π} (\frac{6 M _{1} M _{2}}{r ^{4}})$
$\Rightarrow F \propto \frac{1}{r ^{4}}$
$∴ \frac{F _{1}}{F _{2}} = (\frac{r _{2}}{r _{1}})^{4}$
$\frac{4.8}{F _{2}} = (\frac{2 r}{r})^{4} = 16$
$\Rightarrow F_{2} = 0.3 N$

Q. Force between two identical bar magnets whose Centres r meter apart is 4.8N when their axis are in the same line. If the separation is increased to 2r meter, the force between them is reduced to: