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Magnetism And Matter

Question
CBSEENPH12037723

At a certain location in Africa, a compass points 12° west of the geographic north. The north tip of the magnetic needle of a dip circle placed in the plane of magnetic meridian points 60° above the horizontal. The horizontal component of the earth's field is measured to be 0.16 G. Specify the direction and magnitude of the earth’s field at the location.

Solution

Given,
Declination,  θ = 12° west
Angle of dip, δ = 60°
Horizontal component of earth's magnetic field is,  BH = 0.16 gauss = 0.16 × 10-4 tesla

Since,               BH = BE cos δ 

                      BE = BHcos δ     = 0.16 × 10-4cos  60°

                          BE = 0.16 × 10-41/2       = 0.32 × 10-4T. 

The earth's field lies in a vertical plane 12° west of geographic meridian at an angle of 60° above the horizontal.