Question

Define angle of inclination (magnetic declination).
In the magnetic meridian of a certain place, the horizontal component of earth's magnetic field is $0.25$ gauss and the dip angle is ${60}^o$. At this place find the value of earth's magnetic field.

Answer 1

Magnetic declination is the angle on the horizontal plane between magnetic north (the direction the north end of a compass needle points, corresponding to the direction of the Earth's magnetic field lines) and true north (the direction along a meridian towards the geographic North Pole).

Since the dip angle at the place is ${60}^{\circ }$, the horizontal component of earth's magnetic field $B_H$ and the earth's magnetic field $B$ are related as $B_H=Bcos\theta$

$⟹B=\frac{B_H}{cos\theta }$

$=\frac{0.25}{cos{60}^{\circ }}gauss$

$=0.5gauss$