# Magnetic Field of a Bar Magnet

## Students’ Learning Outcomes

Conduct an experiment to show the magnet field of a bar magnet.

### Information for Teachers

·         Every magnet has two poles.
·         The force of the magnet has an effect in the space around it. This space is called a magnet field.
·         The magnet force is greater near the poles of magnet.
·         The magnet field is invisible but this can be shown using iron filings.

Material / Resources

Magnet, iron nail, common pins, iron filings, textbook.

#### Worm up Activity

1.       What different properties of magnet?
2.       Why the magnet attracts the things made of iron?
3.       Can a magnet attract iron things placed anywhere around it?
4.       On which factors does the attraction of a magnet depend upon?
5.       Is the attraction same at all places around the magnet?
6.       Is magnet field same at all places around the magnet?
7.       Where is the field of a magnet strong and where is it weak?
·         Announce that in this lesson, they will verify these predictions one by one.

#### Activity 1

·         Divide the students into groups of 4-5.
·         Give each group a bar magnet and an iron nail.
·         Ask them to fix a paper sheet on the table with a cello tape and place a bar magnet on it.
·         Ask them to put an iron nail near one pole of the magnet.
·         Ask them: Has the nail stuck to the magnet?

(Expected response: Yes)

·         Ask them to increase the distance of the nail from the magnet.
·         Ask them what do they observe?
(Expected response: The magnet pulls the nail towards it from some distance around it. At a certain distance, it can’t attract the nail).
·         Now ask the students to place the nail at a different location keeping the distance from the magnet same. Ask them to continuously change the location of the nail around the magnet keeping the distance from the magnet same.
·         Now ask what do they observe?
(Expected response: When the nail is placed near poles, it is attracted by the magnet and stuck to it but when it is placed at the center of the magnet, without changing distance from the magnet, it doesn’t stick to the magnet).
·         After this activity tell the students that the space around the magnet where it exerts force of attraction is called its magnet field.
·         As the distance of the nail from the magnet increases the force of attraction of the magnet goes on decreasing and at last after a certain distance it vanishes. Similarly when the nail is placed around the magnet at a different points at the same distance, it is attracted with greater force at the poles, and will less force in the middle.

#### Activity 2

·         Divide the students into groups.
·         Give each group a bar magnet, a glass plate and iron filings.
·         Ask them to put the bar magnet preferably in north-south direction under the glass plate.
·         Ask them to pour small amounts of iron filings step by step on the glass plate.

·         Ask them: What happens to the iron filings?

(Expected response: The iron filings spread in a particular pattern).
·         Ask them to tape the plate gently. Then ask them: What happens to the iron filings?
(Expected response: The pattern of iron filings has improved and looks as if the filings have
arranged in particular lines).

#### Activity 3

·         Divide the students into groups.
·         Give each group a bar magnet, white paper, drawing board and a compass.
·         Ask them to fix the white paper on the drawing board.

·         Ask them to place the bar magnet at the center of the paper such that its north pole points towards the north and south pole points towards the south.

·         Instruct them to mark the outer boundary of the magnet with a pencil.
·         Ask them to put a compass near the north pole of the magnet.
·         Ask them to observe that the south end of the compass needle moves towards the north pole of magnet and the north ends of the compass needle moves away from the north pole of magnet.
·         Instruct them to mark two points on the paper at both ends of the compass needle.
·         Now ask them to move the compass away to place the south end of its needle near the second point.
·         Ask them to mark a third point against the north end of the compass needle.
·         Ask them to go on marking points one by one with the pencil in the same way, until the compass reaches the south pole of the magnet.
·         Instruct them to join all the points by line.
·         Ask them to draw many such lines around the magnet by repeating this action.
·         Now ask them: Are the line patterns similar in both of the above activities?
·         After students’ response tell them that the lines drawn around the magnet in this way are called the magnet lines of force.
##### Sum up / Conclusion
·         The space around the magnet where it has the magnetic effect is called as magnet field.
·         The magnet field is strong near the poles of the magnet.
·         The magnet lines of force start from North Pole and end at South Pole of the magnet.

·         The direction of magnet lines of force shows the pattern of magnet.

##### Assessment
·         Ask the students the following questions:
1.       What do you mean by magnet field?
2.       What are magnet lines of force?
3.       On which factors does the magnet force depend?
4.       If a compass is placed on the middle of a bar magnet, in which direction will be the compass needle move?