Q1. The horizontal component of the earth's magnetic field at a place is 3.2 × 10^-5 tesla, and the angle of dip is 60°. The resultant intensity of the earth's magnetic field at that place is:
A 3.2 × 10^-5 T
B 1.6 × 10^-5 T
C 6.4 × 10^-5 T Correct
D 12.8 × 10^-5 T
Explanation
For the earth's magnetic field, the horizontal component is H = B cos δ, where B is the resultant field and δ is the angle of dip. Here H is 3.2 × 10^-5 T and δ is 60°, so B = H / cos 60° = 3.2 × 10^-5 / 0.5 = 6.4 × 10^-5 T. The value 3.2 × 10^-5 T is only the horizontal component, not the resultant. The value 1.6 × 10^-5 T would come from multiplying by cos 60°. The value 12.8 × 10^-5 T doubles the correct result unnecessarily.