A domain in ferromagnetic substance is in the form of a cube of side `10 ^(-6)m.` Find the number of atoms in the domain.
[Molecular mass of the substance is `7.9 xx 10^(-12)g` and dipole moment per atom is `9.3 xx 10^(-24) A-m^(2)`]

Explanation

Volume of the domain.
`V = (10 ^(-6) cm) ^(3) = 10 ^(-18) cm ^(3)`
Again,` P = 9.3 xx 10 ^(-24) A - m ^(3)`
`M = 7. 9 xx 10 ^(-12) g`
Atomic mass = 55 g/mol
Number of atoms per gram `= ( 6. 02 xx 10 ^(23))/(55)`
`therefore` Number of atoms in `7.9 xx 10 ^(-12) g ` is
`= ( 6. 02 xx 10 ^(23))/( 55) xx 7. 9 xx 10 ^(-12)`
`= 8. 62 xx 10 ^(10)`