Chapter 4: Exploring Magnets

Bhupendra Rawat -


 Chapter 4: Exploring Magnets

1. Magnets

  • A magnet is a material that attracts certain objects, especially those made of iron.
  • Naturally occurring magnets are called lodestones.
  • Magnets made by humans are called artificial magnets.

Magnets are available in different shapes, such as:

  •   Bar magnet
  •   U-shaped magnet
  •   Ring magnet
  •   Disc magnet
  •   Cylindrical magnet
  •   Spherical magnet

2. Magnetic and Non-Magnetic Materials

Magnetic Materials:- Materials that are attracted towards a magnet are called magnetic materials.

Examples:

  • Iron
  • Nickel
  • Cobalt
  • Some alloys containing these metals

Non-Magnetic Materials:- Materials that are not attracted towards a magnet are called non-magnetic materials.

Examples:- Wood, plastic, glass and rubber.

  

3. Poles of a Magnet:- Every magnet has two poles:

1. North Pole (N)

2. South Pole (S)

  •    Iron filings are attracted most strongly near the ends of a magnet.
  •    These ends are called the poles.
  •    The magnetic force is strongest near the poles.
  •    A magnet always has both poles.
  •    A single North or South pole cannot exist.
  •    Even if a magnet is broken into smaller pieces, each piece has both a North and a South pole.

   

4. Finding Directions Using a Magnet

  • When a bar magnet is freely suspended, it always comes to rest approximately in the North–South direction.
  • The end pointing towards North is called the North pole.
  • The other end is called the South pole.
  • This happens because the Earth behaves like a giant magnet.
  • A freely suspended ordinary iron bar does not always point North–South. This property helps us identify a magnet.

 5. Magnetic Compass:- A magnetic compass is a device used to find directions.

Main features:

  • It contains a small magnetised needle.
  • The needle can rotate freely.
  • It settles in the North–South direction.
  • A dial shows the different directions.
  • The North-pointing end of the needle is usually marked or painted red.

Use: A compass helps travellers, sailors and others find directions.

    Making a Simple Compass:- A simple compass can be made using:

  • Iron sewing needle
  • Bar magnet
  • Cork
  • Bowl
  • Water

The needle is magnetised by repeatedly rubbing one pole of a magnet along it in the same direction. The magnetised needle is then placed through a cork and floated on water. It settles in the North–South direction.

An ancient Indian device called Matsya-yantra (Machchh-yantra) used a magnetised fish-shaped iron piece kept in oil for navigation.

7. Attraction and Repulsion:- When two magnets are brought close together:

Poles Effect

North – North Repulsion

South – South Repulsion

North – South Attraction

Rule to remember:

Like poles repel and unlike poles attract.

- N + N → Repel

- S + S → Repel

- N + S → Attract

Important Point:- A magnet can be identified by its ability to repel another magnet.

An ordinary iron bar is attracted by both poles of a magnet, whereas two magnets can show either attraction or repulsion.

 8. Magnetic Effect Through Materials:- Magnetic force can act through some non-magnetic materials.

For example, a magnet can affect a compass needle even when materials such as:

  • Wood
  • Cardboard
  • Plastic
  • Glass

are placed between them.

9. Uses and Fun with Magnets:- Magnets can be used to:

  • Close pencil boxes and purses.
  • Hold objects on boards.
  • Move steel balls through a maze.
  • Pick up steel objects from water without touching them directly.
  • Make magnetic toys and cars.
  • Find directions using a compass.

Magnets can sometimes move objects without touching them.

10. Care of Magnets:- Magnets should be handled carefully.

  • Do not heat magnets.
  • Do not drop or hammer them.
  • Keep them away from mobile phones and remote controls.
  • Store magnets properly.
  • Keep magnets in pairs with unlike poles on the same side.
  • A wooden piece and soft iron pieces can be used while storing certain bar magnets.

Answers to “Let Us Enhance Our Learning”
1. Fill in the blanks
(i) Unlike poles of two magnets attract each other, whereas like poles repel each other.
(ii) The materials that are attracted towards a magnet are called magnetic materials.
(iii) The needle of a magnetic compass rests along the north-south direction.
(iv) A magnet always has two poles.     
2. State whether the following statements are True (T) or False (F)
(i) A magnet can be broken into pieces to obtain a single pole. False (F)
(ii) Similar poles of a magnet repel each other. True (T)
(iii) Iron filings mostly stick in the middle of a bar magnet when it is brought near them. False (F)
(iv) A freely suspended bar magnet always aligns with the north-south direction. True (T)     Chapter - 4 Exploring Magnets
3. Fill in the blanks in Column II
Column I – Poles                                             Column II – Interaction
  • N – N                                                             Repulsion
  • S – N                                                             Attraction
  • N – S                                                             Attraction
  • S – S                                                             Repulsion
Rule: Like poles repel each other, while unlike poles attract each other.     
4. Atharv’s experiment
Question: Atharv rolled a bar magnet over a heap of steel U-clips. Which observation is likely?
Answer: (i) 10, 2, 10
Reason: The magnetic force is strongest near the two poles/ends of a magnet. Therefore, more U-clips will be attracted at Positions A and C, while fewer will be attracted at the middle Position B.     
5. Identifying the two magnets
Question: Reshma has three identical metal bars. Two are magnets and one is an iron bar. How can she identify the two magnets without using any other material?
Answer:
Take any two bars and bring one end of the first bar close to one end of the second bar. Repeat the test with different ends.
- If repulsion is observed between two bars, both bars are magnets.
- The iron bar will be attracted by both poles of a magnet and will not show repulsion.
Thus, the pair that shows repulsion consists of the two magnets.    
6. Finding the poles of an unmarked magnet
Question: You are given a magnet whose poles are not marked. How can you find its poles using another magnet with marked poles?
Answer:
Bring the known North pole of the marked magnet close to one end of the unmarked magnet.
- If that end is repelled, it is the North pole.
- If it is attracted, it is the South pole.
Then the other end will have the opposite polarity.
7. Finding the North pole without another magnet
Question: A bar magnet has no markings. How would you find out near which end its North pole is located without using another magnet?
Answer:
Suspend the bar magnet freely with a thread and allow it to come to rest. The end that points towards the North direction is the North pole. The other end is the South pole.     Chapter - 4 Exploring Magnets
8. Earth as a magnet
Question: If Earth is itself a magnet, can you guess the poles of Earth's magnet by looking at the direction of a magnetic compass?
Answer:
A compass needle's North pole points towards the geographical North direction. Therefore, the region near Earth's geographical North behaves like a magnetic South pole, while the region near the geographical South behaves like a magnetic North pole.
9. Helping the mechanic
Question: Steel screws kept falling from the screwdriver. Suggest a solution.
Answer:
The mechanic can magnetise the screwdriver by repeatedly rubbing it with one pole of a magnet in the same direction. The magnetised screwdriver will attract and hold the steel screws, making the work easier.
10. Two ring magnets X and Y
Question: Magnet X does not move down further towards magnet Y. What could be the reason? How can X be brought into contact with Y without pushing either magnet?
Answer:
The like poles of X and Y are probably facing each other. Therefore, they repel each other.
To bring them into contact, turn one of the magnets around so that unlike poles face each other. They will then attract each other and move together.     Chapter - 4 Exploring Magnets
11. Finding the polarity of the magnets
Question: Three magnets are arranged as shown in Fig. 4.17. The polarity of end 5 is given as N. Find the polarity at ends 1, 2, 3, 4 and 6.
Answer:
- 1 – S
- 2 – N
- 3 – S
- 4 – N
- 5 – N (given)
- 6 – S
Reason: Each magnet has North and South poles, and the arrangement follows the rule that like poles repel and unlike poles attract.

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