Question

A ship has to reach a place which is due west from its present position. Declination at this point is${15^ \circ }$. The direction from the compass needle in which it should sail is:
A. ${75^ \circ }$
B. ${15^ \circ }$
C. ${105^ \circ }$
D. ${165^ \circ }$

Answer 1

Magnetic declination or magnetic variation is the angle on the horizontal plane between the magnetic meridian and the true meridian. The angle of variation depends on the position on the earth’s surface and changes over time, and this angle is expressed in degrees and minutes. A compass refers to an instrument used for navigation and orientation that shows direction relative to the geographic points.
In this question, we need to determine the direction from the compass needle in which it should sail. For this we will use the generalization of the compass.

Complete step by step answer: Given declination at the point is ${15^ \circ }$and the ship is selling in the west direction.
As we know the magnetic declination at a place is the anf=gle between the magnetic and true meridian.
Here declination at the point is given ${15^ \circ }$, and this angle is between magnetic north and true north.
Now let ${N_t}$and${S_t}$ represent the true north and south direction.
${N_m}$and ${S_m}$represents the magnetic north and south.

Given that the true north is at ${N_t} = {15^ \circ }$ from compass needle hence the true or the geographical south will be at an angle ${S_t} = {90^ \circ } - {15^ \circ } = {75^ \circ }$
Therefore we can say the ship should sail at ${75^ \circ }$ from compass needle direction.
Option A is correct.

Note: Students must note that the earth’s magnetic poles are at some distance from its geographic poles; hence declination is observed in compass. The term magnetic deviation is approximately the same as magnetic declination, but more correctly, it refers to the error in a compass reading due to nearby metallic objects.