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Magnetism And Matter

Question
CBSEENPH12037795

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 field is measured to be 0.16 G. Specify the magnitude of the earth's field at the location.

Solution

Given,
Horizontal component of Earth's magnetic field = 0.16 G
θ = 60o 
Using the formula,
                            BH = B cosθ 
        B = 0.16cos 60 = 0.160.5 = 0.32 G

which is the required magnitude of earth.