Question

Sindbad the sailor, on one of his voyages lost the direction in sea, then has used ______ and came to know that his ship is heading towards south.
A. Compass
B. Magnetometer
C. Bar magnet
D. Galvanometer

Answer 1

According to modern earth’s magnetism theory, Earth has both geographic poles and magnetic poles. These poles of the earth’s magnet produce magnetic fields surrounding the earth. Just like the magnetic field produced around a permanent magnet has different magnetic intensities at different points, total magnetic intensity at different locations of earth also varies from place to place. Total magnetic intensity (B) has two components. One is the vertical component $({B_V})$ and the other is horizontal component $({B_H})$.

Complete step by step answer:
It is well known that the earth has a magnetic field associated with it. It has both horizontal and vertical components of magnetic field at every location and the resultant of horizontal component and vertical component at a particular place gives us the resultant magnetic field at that location. Dip is the angle between the resultant magnetic field vector and the horizontal component vector. Horizontal component of the magnetic field always points in the north direction.
The angle between the resultant total magnetic field(B) vector at a particular location and its horizontal component $({B_H})$ vector is called a dip at a particular location.
Let dip angle be $\theta$
According to formula
${B_H} = B\cos (\theta )$

Declination is the angle between horizontal components of magnetic field(${B_H}$) i.e magnetic meridian and geographical meridian.
That declination can also be expressed in terms of dip angle. That is the angle between $B\cos (\theta )$ and magnetic meridian at particular places.
Declination is measured by magnetic compass and it is used to find the geographical directions.
Hence option A will be the answer.

Note:
Magnetic compass shows us the geographic directions whereas there is a dip circle which aligns itself along the direction of resultant earth’s magnetic field at that particular direction. I.e magnetic needle aligns along ${B_H}$ while dip needle aligns along the resultant of ${B_V}$ and ${B_H}$ at a particular place. If we have a horizontal component or vertical component and dip angle we can get a resultant magnetic field at a place.