EXPERIMENT – 5

AIM:

To draw the lines of force around a bar magnet placed in the magnetic maredian with its north pole facing the geographical north and to obtain the null points.

APPARATUS:

Drawing board, paper, cello tape magnetic compass needle and a bar magnet.

THEORY:

A bar magnet creates a magnetic field around itself and at the same time the earth also has a uniform magnetic field at a given location. When the combined magnetic field is plotted around the bar magnet, then there are certain points where the magnetic field due to the bar magnet is equal and opposite to the magnetic field due to the earth. These points are called null points.

PROCEDURE:

1.Fix a sheet of paper on the drawing board with cello tape.
2. Draw a line in the middle of the paper and put a compass needle on the line.
3. Rotate the drawing board such that the direction of the compass needle coincides with the direction of the line drawn. Remove the compass needle.
4. Put the bar magnet on the paper such that its long edge touches the line and the north pole of the magnet points towards the geographic north. Mark the outline of the magnet and the drawing board to make sure that both are not disturbed during the experiment.
5. Put the compass needle near the north pole of the bar magnet and mark dots at the ends of the needle with a pencil.
6. Pick the compass needle and place it in such a manner that the south end is kept at the point where the north end was earlier located. Go on repating this process till you reach the other end of the magnet. In this way a line of force has been located.
7. Starting from different points near the north pole of the bar magnet, several such lines are drawn.
8. At the location of neutral points the compass needle does not experience any force.

PRECAUTIONS:

1. The position of the magnet and the drawing board should not be disturbed during the entire experiment.
2. No magnet or magnetic substance should be kept near the board.
3. The magnetic needle should be kept exactly on the dot previously obtained.

RESULT:

The magnetic field and the null points are as shown in the figure.