( v ) Isodynamic Line A line joining places of equal horizontal component of earth ’ s magnetic field ( H ) is called an isodynamic line .
Magnetic Latitude
( i ) If at any place , the angle of dip is δ and magnetic latitude is λ then tan δ = 2 tan λ
( ii ) The total Intensity of earth ’ s magnetic field I = I 0 √1 + 3 sin 2 λ where I o = M / R 3
It is assumed that a bar magnet of earth has magnetic moment M and radius of earth is R .
( Magnetic maps are maps obtained by drawing lines passing through different places on the surface of earth , having the same value of a magnetic element .)
Neutral Points
Neutral point of a bar magnet is a point at which the resultant magnetic field of a bar magnet and horizontal component of earth ’ s magnetic field are zero .
When north pole of a bar magnet is placed towards south pole of the earth . then neutral point is obtained on axial line .
B = μ o / 4π 2Mr / ( r 2 – l 2 ) 2 = H If r > > l , then B = μ o / 4π 2M / r 3 = H
When north pole of a bar magnet is placed towards north pole of the earth , then neutral point is obtained on equatorial line
B = μ o / 4π 2Mr / ( r 2 + l 2 ) 2 = H If r > > l , then B = μ o / 4π 2M / r 3 = H
Tangent Law
When a bar magnet is freely suspended under the combined effect of two uniform magnetic fields of intensities B and H acting at 90 ° to each other , then it bar magnet comes to rest making an angle 0 with the direction of H , then
B = H tan θ