Question

At a certain location in Africa, compass points ${12}^o$ west of geographic north. The north tip of magnetic needle of a dip circle placed in the plane of magnetic meridian points ${60}^o$ above the horizontal. The horizontal component of earth's field is measured to be $0.16$G. The magnitude of earth's field at the location is?

• A. $0.32$G
• B. $0.42$G
• C. $4.2$G
• D. $3.2$G

Answer 1

Answer: (A)

$0.32$G

Here, $H_E=0.16G=0.16\times {10}^{-4}$T,
dip angle $\left(\delta \right)={60}^o$
Then, magnitude of earth's field.

$B_E=\frac{H_E}{\cos \delta }=\frac{0.16\times {10}^{-4}}{\cos {60}^o}T\Rightarrow B_E=\frac{0.16\times {10}^{-4}}{\frac{1}{2}}$

$=0.32\times {10}^{-4}T=0.32G$