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Magnetism And Matter

Question
CBSEENPH12037755

A magnetic needle free to rotate in a vertical plane, orients itself with its axis vertical at a certain place on the earth. What are the values of (a) horizontal component of earth’s field? (b) angle of dip at this place?

Solution
The place is clearly the magnetic pole of earth as needle rotates in vertical plane and, not in horizontal plane we have,
                     B
H = 0 . 
Hence, 
(a) Horizontal component of earth's magnetic field at the magnetic poles, BH = 0 .
(b) Angle of dip at the magnetic poles of earth, δ = 90°.