Grade 6 Ch 4 Exploring Magnets

 

Class 6 Ch 4 Exploring Magnets

1. Introduction to Magnets

Magnets are objects that possess the property of attracting certain materials. Their use in navigation dates back to ancient times when sailors used devices like the magnetic compass to find directions, especially when celestial bodies like stars were not visible.

• Natural vs. Artificial Magnets:
• Natural Magnets: The earliest known magnets were naturally occurring rocks called lodestones, discovered in ancient times.
• Artificial Magnets: Most magnets used today are man-made from materials like iron or combinations of different metals. These are found in everyday items such as pencil boxes, toys, stickers, and school laboratory equipment.
• Shapes of Magnets: Artificial magnets are created in various shapes and sizes to suit different needs. Common shapes include the bar magnet, U-shaped magnet, ring magnet, cylindrical magnet, disc magnet, and spherical magnet.

                                 Figure: Types of magnets: (a) Natural; (b) Artificial.

Types of Magnets

1. Bar Magnet: A rectangular magnet with two poles at each end.
2. Horseshoe Magnet: Shaped like a horseshoe and has poles at its two ends.
3. Ring Magnet: A circular magnet with a hole in the center.
4. Electromagnet: A temporary magnet created by passing electric current through a coil wrapped around iron. Electromagnets are used in electric motors, cranes, and electrical devices.

2. Magnetic and Non-Magnetic Materials

Materials can be classified based on their interaction with magnets.

• Magnetic Materials: These are materials that are attracted to a magnet. The primary examples are the metals iron, nickel, and cobalt. Certain combinations of these metals with others can also be magnetic.
• Non-Magnetic Materials: These are materials that are not attracted to a magnet. Examples include wood, rubber, plastic, and glass.

3. The Poles of a Magnet

A magnet’s attractive force is not uniform across its entire surface.

• North and South Poles: The magnetic force is strongest at the ends of a magnet. These two ends are called the poles. One is designated the North pole (N) and the other is the South pole (S). This is observable by spreading iron filings on a bar magnet; the filings will cluster most densely at the two poles.
• Poles Exist in Pairs: A fundamental property of magnets is that poles always exist in pairs. It is impossible to isolate a single North pole or a single South pole. If a magnet is broken into smaller pieces, each new piece will have its own North and South poles.

4. Direction-Finding Properties

The most significant property of a magnet, historically, is its ability to indicate direction.

• North-South Alignment: When a bar magnet is suspended freely (e.g., by a thread tied to its middle), it will always come to rest pointing in the Earth’s north-south direction. This occurs because the Earth itself behaves like a giant magnet.
• Naming the Poles:
• The end of the magnet that points towards the geographic North is called the North-seeking pole, or simply the North pole.
• The end that points towards the geographic South is called the South-seeking pole, or the South pole.
• Test for a Magnet: This alignment property is unique to magnets. An unmagnetized iron bar, if freely suspended, will come to rest in any random direction. This provides a method to determine if a piece of metal is a magnet.

5. The Magnetic Compass

                                                 Figure: A magnetic compass.
The direction-finding property of magnets led to the development of the magnetic compass.

• Construction: A typical magnetic compass consists of a small, lightweight magnetized needle balanced on a pin inside a circular box with a transparent cover. The needle can rotate freely. Below the needle is a dial with directions (North, South, East, West) marked on it. The end of the needle pointing North is often painted red.
• Function: When placed on a horizontal surface, the compass needle aligns itself with the north-south direction. The user then rotates the compass box until the ‘N’ and ‘S’ on the dial line up with the corresponding ends of the needle, allowing for the determination of all other directions.

6. Creating Your Own Magnet

It is possible to magnetize a piece of iron, such as a sewing needle.

• Method: Place an iron needle on a flat surface. Stroke it along its length with one pole of a permanent bar magnet, always moving in the same direction (from one end to the other). Lift the magnet at the end of each stroke and return to the starting point to begin the next stroke. Repeating this process 30 to 40 times will magnetize the needle.

• Homemade Compass: A simple compass can be made by passing this newly magnetized needle through a piece of cork and floating it in a bowl of water. The needle will align itself in the north-south direction. An ancient Indian navigational device called the matsya-yantra operated on a similar principle, using a magnetized fish-shaped piece of iron in a vessel of oil.

7. Attraction and Repulsion

When two magnets are brought near each other, they exert forces on one another.

• The Law of Poles:
• Unlike poles attract: The North pole of one magnet will attract the South pole of another.
• Like poles repel: The North pole of one magnet will repel the North pole of another. Similarly, two South poles will repel each other.
• The Surest Test for Magnetism: Repulsion is the definitive test to identify a magnet. A magnet will attract a piece of unmagnetized iron at both of its ends, but it will only repel another magnet when like poles are brought together.

8. Magnetic Force Through Materials

Magnetic force is not blocked by all materials. Experiments show that the magnetic effect can act through non-magnetic materials such as wood, cardboard, thin plastic, and glass. Placing these materials between a magnet and a compass needle does not cause any appreciable change in the needle’s deflection.

9. Handling and Storing Magnets

Magnet Safety Tips

While using magnets, certain precautions should be followed.

Safety tips include:

• Do not heat magnets.
• Do not hammer magnets.
• Avoid dropping magnets.
• Store magnets properly to maintain their strength.
• Keep magnets away from devices like mobile phones and remote controls.

Improper handling can weaken or demagnetize magnets.

Proper Storage: To preserve their strength, 

• Bar magnets should be stored in pairs with their unlike poles on the same side. 
• A piece of wood should be placed between them, and two pieces of soft iron (keepers) should be placed across their ends.

 

Question 1. Fill in the blanks

(i) Unlike poles of two magnets _______ each other, whereas like poles each other.
(ii) The materials that are attracted towards a magnet are called _______ .
(iii) The needle of a magnetic compass rests along the _______ direction.
(iv) A magnet always has ______ poles.

Answer: (i) attract, repel           (ii) magnetic materials.          (iii) north-south           (iv) two.

Question 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. [ ]
(ii) Similar poles of a magnet repel each other. [ ]
(iii) Iron filings mostly stick in the middle of a bar magnet when it is brought near them. [ ]
(iv) A freely suspended bar magnet always aligns with the north-south direction. [ ]

Answer:  (i) False            (ii) True            (iii) False          (iv) True

Question 3. Column I shows different positions in which one pole of a magnet is placed near that of the other. Column II indicates the resulting interaction between them for different situations. Fill in the blanks.

Answer:

Column I	Column II
N – N	Repulsion
N – S	Attraction
S – N	Attraction
S – S	Repulsion

Question 4. Atharv performed an experiment in which he took a bar magnet and rolled it over a heap of steel U-clips (Fig. 4.15).

According to you, which of the options given in Table 4.3 is likely to be his observation?

Answer: From the figure, it is clear that the ends of the magnet have more iron fillings attached to it. This is because the strength of a magnet lies more at the ends of the magnet. Hence option (i) is correct.

Question 5. Reshma bought three identical metal bars from the market. Out of these bars, two were magnets and one was just a piece of iron. How will she identify which two amongst the three could be magnets (without using any other material)?

Answer: Reshma can use the property of repulsion to identify the magnets. She can bring the ends of two bars close to each other. If there is repulsion between any two bars, those two must be magnets (because only magnets repel each other). If there is only attraction, it means one is a magnet and the other is iron.

Question 6. You are given a magnet which does not have the poles marked. How can you find its poles with the help of another magnet which has its poles marked?

Answer: Bring the known North pole of the marked magnet close to one end of the unmarked magnet. If the ends attract, then the unmarked end is a South pole. If they repel, the unmarked end is a North pole.

Question 7. A bar magnet has no markings to indicate its poles. How would you find out near which end its North pole is located without using another magnet?

Answer: Suspend the bar magnet freely using a thread. Once it comes to rest, the end pointing towards the geographic North is the North pole of the magnet, and the opposite end is the South pole.

Question 8. If the earth is itself a magnet, can you guess the poles of earth’s magnet by looking at the direction of the magnetic compass?

Answer: Yes, the end of the compass needle that points towards the geographic North is the magnet’s North-seeking pole (which is actually the magnetic South pole of the Earth). Hence, the Earth’s magnetic South pole is located near the geographic North pole, and the magnetic North pole is near the geographic South pole.

Question 9. While a mechanic was repairing a gadget using a screw driver, the steel screws kept falling down. Suggest a way to solve the problem of the mechanic on the basis of what you have learnt in this chapter.

Answer: The mechanic can magnetize the screwdriver by stroking it several times with a magnet in one direction. This will allow the screwdriver to attract and hold the screws, preventing them from falling.

Question 10. Two ring magnets X and Y are arranged as shown in Fig. 4.16. It is observed that the magnet X does not move down further. What could be the possible reason? Suggest a way to bring the magnet X in contact with magnet Y, without pushing either of the magnets.

Answer: The reason magnet X does not move down further is due to the repulsion between like poles (e.g., both North poles or both South poles) of the two magnets. To bring magnet X into contact with magnet Y, you can flip one of the magnets so that unlike poles (North and South) face each other, allowing them to attract.

Question 11. Three magnets are arranged on a table in the form of the shape shown in Fig. 4.17. What is the polarity, N or S, at the ends 1, 2, 3, 4 and 6 of the magnets? Polarity of one end (5) is given for you.

Answer:

Point	Polarity
1	North (N)
2	South (S)
3	North (N)
4	South (S)
6	North (N)

Polarity at end 5 is already given as South (S).

(Page 62)

Question. Do magnets stick to objects made of certain materials only?

Answer: Yes, magnets stick only to objects made of magnetic materials. These materials are generally metals like iron, nickel, and cobalt. Materials like wood, plastic, and glass are non-magnetic and are not attracted by magnets.

(Page 64)

Question. Do all parts of a magnet attract magnetic materials equally?

Answer: No, not all parts of a magnet attract magnetic materials equally. The magnetic force is strongest at the poles of the magnet (the North and South poles), where most of the magnetic materials get attracted. The middle part of the magnet has a much weaker magnetic effect.

(Page 65)

Question. Can we find a magnet with a single pole?

Answer: No, it is not possible to find a magnet with a single pole. Every magnet always has both a North and a South pole. If a magnet is broken into smaller pieces, each piece will still have both poles, no matter how small the piece is.