CBSE Class 6- Science Chapter 4: Mindful Eating: Exploring Magnets- Study Notes (PDF)

Study Notes: Exploring Mangents (Class 6-NCERT(Curiosity) Science

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.

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

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

Magnets can lose their magnetic properties if not handled with care.

• Cautions: Do not heat, drop, or hammer a magnet, as this can weaken or destroy its magnetism. Keep magnets away from devices like mobile phones and remote controls.
• 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.

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Short-Answer Quiz

Answer the following questions in 2-3 sentences each.

1. What is the primary difference between magnetic and non-magnetic materials? Provide an example of each.
2. Describe what happens when a bar magnet is suspended freely and explain the scientific reason for this behavior.
3. State the fundamental law that governs the interaction between the poles of two magnets.
4. Why is repulsion, and not attraction, considered the definitive test to determine if an object is a magnet?
5. What are the “poles” of a magnet, and where is a magnet’s attractive force concentrated?
6. If you break a bar magnet in half, do you get one piece with a North pole and one with a South pole? Explain.
7. Briefly describe how a magnetic compass works to indicate direction.
8. Outline the single-stroke method used to turn an ordinary iron sewing needle into a magnet.
9. What are three specific actions that should be avoided to prevent a magnet from losing its properties?
10. Differentiate between a natural magnet and an artificial magnet.

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Answer Key

1. The primary difference is their response to a magnetic field. Magnetic materials, such as iron, nickel, and cobalt, are attracted towards a magnet. Non-magnetic materials, like wood, plastic, or rubber, are not attracted towards a magnet.
2. When a bar magnet is suspended freely, it aligns itself to point in the Earth’s north-south direction. This happens because the Earth itself acts as a giant magnet, and its magnetic field exerts a force on the suspended magnet, causing it to align with the field.
3. The fundamental law of magnetic poles states that unlike poles attract each other (North attracts South), while like poles repel each other (North repels North, and South repels South).
4. Repulsion is the definitive test because a magnet can attract both another magnet (at its opposite pole) and an unmagnetized magnetic material like iron. However, a magnet will only repel another magnet, making repulsion a unique interaction between two magnets.
5. The “poles” of a magnet are the two ends where its magnetic strength is most concentrated. These are known as the North pole and the South pole. When iron filings are sprinkled on a magnet, they stick most densely to these polar regions.
6. No, you do not get two separate, single-poled pieces. A single magnetic pole cannot exist. When a bar magnet is broken, each new piece will instantly become a smaller, complete magnet with its own North and South pole.
7. A magnetic compass contains a freely rotating magnetized needle that aligns itself with the Earth’s magnetic north-south direction. By observing the needle’s orientation against a dial marked with directions, a user can determine their bearing.
8. To magnetize an iron needle, one pole of a strong magnet is placed at one end of the needle and stroked along its entire length. The magnet is lifted at the far end and brought back to the start to repeat the stroke, always in the same direction, for 30-40 times.
9. To prevent a magnet from losing its properties, one should not heat it, drop it from a height, or hammer it. These actions can disrupt the internal alignment that gives the magnet its strength.
10. A natural magnet is a naturally occurring material, like a lodestone, which has magnetic properties. An artificial magnet is a man-made object, created by magnetizing materials like iron or cobalt, and can be formed into various shapes like bars or rings.

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Essay Questions

Consider the following prompts for deeper analysis and discussion.

1. Discuss the historical importance of magnetism in human exploration and navigation. Trace the evolution from the use of natural lodestones to the development and function of the modern magnetic compass as described in the text.
2. You are given three identical-looking metal bars. You are told that two are magnets and one is an unmagnetized piece of iron. Without using any other equipment, describe a systematic procedure to identify which two bars are the magnets and which one is the iron bar.
3. Explain in detail the concept of magnetic poles, including their properties of attraction and repulsion. Use the information from the provided activities to illustrate how these properties can be observed and how they distinguish magnets from other materials.
4. Based on the text, elaborate on the statement: “our Earth itself behaves like a giant magnet.” How does this property of the Earth explain the behavior of a freely suspended magnet and the functionality of a compass?
5. Analyze the ways in which magnetic properties can be manipulated for practical and recreational purposes. Using examples from the text, describe how to create a magnet, how to build a simple compass, and how magnetic forces can be used in “fun activities” without physical contact.

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Glossary

Term	Definition
Artificial Magnet	A magnet that is made by people from materials like iron, as opposed to occurring naturally.
Attraction	The force that pulls magnets or magnetic materials towards each other, such as when unlike poles (N-S) are brought together.
Bar Magnet	A common artificial magnet in the shape of a rectangular bar with a North pole at one end and a South pole at the other.
Cobalt	A metal that is a magnetic material, meaning it is attracted to magnets.
Iron	A metal that is a magnetic material. Most artificial magnets are made from pieces of iron.
Lodestone	A naturally occurring magnetic rock, representing the earliest known type of magnet.
Magnetic Compass	A navigational device containing a freely rotating magnetized needle that aligns with the Earth’s north-south direction to indicate direction.
Magnetic Materials	Materials that are attracted towards a magnet, such as iron, nickel, and cobalt.
Matsya-yantra	An ancient Indian navigational device consisting of a magnetized, fish-shaped piece of iron kept in a vessel of oil.
Nickel	A metal that is a magnetic material, meaning it is attracted to magnets.
Non-magnetic Materials	Materials that are not attracted towards a magnet, such as wood, plastic, rubber, and glass.
North Pole	One of the two ends of a magnet where the magnetic force is strongest; it is the end that points towards the geographic North when freely suspended. Also known as the North-seeking pole.
Repulsion	The force that pushes two magnets away from each other, occurring when like poles (N-N or S-S) are brought together.
Ring Magnet	An artificial magnet shaped like a ring or donut.
South Pole	One of the two ends of a magnet where the magnetic force is strongest; it is the end that points towards the geographic South when freely suspended. Also known as the South-seeking pole.
U-shaped Magnet	An artificial magnet bent into the shape of a ‘U’.