Question

The vertical component of the earth’s magnetic field is:
A. Zero at the magnetic pole
B. Zero at the geographic pole
C. same everywhere
D. Zero at magnetic equator

Answer 1

Hint: First we will discuss how the magnetic field lines appear for a permanent magnet. Then we will talk about the arrangement of magnetic poles of the earth and then draw the magnetic field lines as they may appear around earth.

Complete step-by-step answer:
Magnetic field lines for a permanent bar magnet originate from the north pole of the magnet and go to the south pole of the magnet. The magnetic field lines originate straight up from a north pole as can be seen in the figure below.

Now we can assume that there is a giant bar magnet inside the surface of the earth but its poles are slightly offset from the geographical poles of the earth. Now if you are standing at one of the magnetic poles, the magnetic field lines would emerge from there vertically upwards, assuming you are standing at the magnetic north pole and they will be going straight down if you are at the magnetic south pole. Now everywhere else on the planet, the magnetic field lines would have a different direction with reference to the surface, so for earth they would look like this

Only one field line is drawn here for clarity. As we can see that only at the poles, the magnetic field is perpendicular to the surface. Hence, there will be no vertical component of the magnetic field there. Of the given option only one condition is satisfied.

So, the correct answer is “Option A”.

Note: Students must remember that magnetic field lines don’t actually exist and are only a method for representation of direction and magnetic field intensity. Here they have been used to show only the direction of the magnetic field and nothing else.