( a ) Deflection method In this method one magnet is used at a time and deflection in galvanometer is observed . Ratio of magnetic dipole moments of the magnets
M 1 / M 2 = tanθ 1 / tanθ 2 where θ 1 and θ 2 are mean values of deflection for two magnets .
( b ) Null method In this method both magnets are used at a time and no deflection condition is obtained . If Magnets are at distance d 1 and d 2 then
M 1 / M 2 = ( d 1 / d 2 ) 3
Tangent Galvanometer
It is a device used for detection and measurement of low electric currents . Its working is based on tangent law . If θ is the deflection produced in galvanometer when I current flows through it , then
I = 2R / Nμ o H tan θ = H / G tan θ = K tan θ
Where G = Nμ / 2R is called galvanometer constant and K = H / G , is called reduction factor of tangent galvanometer .
Here N is number of turns in the coil and R is radius of the coil . Tangent galvanometer is also called moving magnet type galvanometer .