Question

Earth's magnetic field may be supposed to be due to a small bar magnet located at the centre of the earth. If the magnetic field at a point on the magnetic equator is 0.3×10^–4 T. Magnet moment of bar magnet is

• A.
• B. $7.8 \times 10 ^ { 22 } \mathrm { amp } \times \mathrm { m } ^ { 2 }$
• C.
• D. None of these

Answer 1

Answer: (B)

$7.8 \times 10 ^ { 22 } \mathrm { amp } \times \mathrm { m } ^ { 2 }$

Answer 2

When a magnet is freely suspended in earth’s magnetic field, it's north pole points north, so the magnetic field of the earth may be suppose to be due to a magnetic dipole with it's south pole towards north and as equatorial point is on the broad side on position of the dipole.

$B _ { c } = \frac { \mu _ { 0 } } { 4 \pi } \cdot \frac { M } { r ^ { 3 } } \Rightarrow 0.3 \times 10 ^ { - 4 } = 10 ^ { - 7 } \times \frac { M } { \left( 6.4 \times \times 10 ^ { 6 } \right) ^ { 3 } }$ A-².