A magnetic needle free to rotate in a vertical plane parallel to the magnetic meridian has its north tip down at `60^(@)` with the horizontal.The horizontal component of the earth's magnetic field at the place is known to be `0.4G`.Determine the magnitude of the earth's magnetic field at the place.

Explanation

`delta=60^(@) H=0.4 G,R=?`
`H=R cos delta`
`R=H/(cosdelta)=0.4/(cos 60^(@))=0.4/(1//2)=0.4xx2`
`R=0.8 G`