Question

Isogonic lines on a magnetic map will have.
A. Zero angle of dip
B. Zero angle of declination
C. The same angle of dip
D. The same angle of declination

Answer 1

Hint: The term ‘Iso’ means constant or same. Also there is a difference between the earth’s magnetic north pole and the earth’s geographic pole and the angle subtended between these two poles is called the angle of declination.

Complete Step-by-Step solution:
There are imaginary magnetic field lines running across the earth that go into the magnetic north pole and emerge from the magnetic south pole. So these magnetic field lines are not straight lines like the latitudes or the longitudes. They are twisted and curved and different in different parts on earth.
The angle of declination is the angle subtended between the earth’s magnetic field and the earth’s geographical north pole. So by convention, the values of the angle of declination is positive for the angles lying on the east side of the horizontal plane which contains the both the axes, with the magnetic axis lying on the right side of the plane and negative if the angle subtended is lies on the east side of the horizontal plane. It is usually denoted by the Greek letter delta $\left( \delta \right)$.

So as I have mentioned the magnetic field lines are not straight lines, so there can be places on the earth where the magnetic field lines will have the same declination. We call these kinds of lines as Isogonic lines.
So the answer to the question is option (D)- Same angle of declination

Note: The magnetic declination at a place changes over time since the magnetic north pole keeps shifting with time, so the angle between the magnetic north pole and geographic north pole changes.
Magnetic declination changes from place to place also. So proper corrections should be made to navigational systems used in aircrafts and ships in order to determine their course correctly.