Question

The lines of force due to earth's horizontal magnetic field are :
A) parallel and straight
B) concentric circles
C) elliptical
D) curved lines

Answer 1

Earth has a permanent magnetic property. Due to this property Earth effects on magnetic substances just like some bar magnet does. So, like every bar magnet earth has also its magnetic field lines around it.

Explanation:
Earth acts as a big bar magnet. Earth’s magnetic field is produced due to the convection of liquid iron alloy inside its outer core. The magnetic field is created in such a way that the whole earth acts as a bar magnet with a magnetic south pole at geographic North Pole and vice versa (see the picture). So magnetic field lines start from magnetic north pole (geographic south pole) and end at magnetic south pole(geographic north). These field lines are curved lines like stretched rubber bands. At any point the tangent on the field line gives the direction of the magnetic field at that point. The density of field lines gives the strength of the magnetic field. These field lines never cross each other and most importantly they complete a continuous loop inside earth. Now, at any point on the earth if a compass is placed then its north will always point toward geographical north and south towards geographical south. At both magnetic poles any freely suspended magnet will stay vertical with the north pole pointing downward at the geographical north and south pole at the geographical south.

Correct answer:The line of force due to earth’s horizontal magnetic field are (d) curved lines.

Additional information:
Axis of earth’s rotation is not perfectly aligned with the line connecting magnetic poles of earth. Approximately they are 11 degrees tilted from each other.

Note: If a bar magnet is freely suspended at any point on earth then one side faces geographic north and other side geographic south. The north seeking pole is named as the North pole of the bar magnet and the other one as the South pole. Then from the property of magnet it was known that opposite poles attract and similar poles repel. Hence, to match with that property Earth must be considered as a big bar magnet with reversed pole direction compared to the geographical pole.