Class 6 Science Chapter 10 Important Questions

• What is magnetite?
  Magnetite is one of the natural ores of iron and also known as “natural magnet”.
• What is magnet? In which country was the magnet used discovered?
  A material which shows an attraction for magnetic materials such as iron, cobalt and nickel is called a magnet. And when it is suspended freely its point shows in the geographical north-south direction.
  Magnet use was first discovered in Greece.

It is said that, there was a shepherd named Magnes, who lived in ancient Greece. He used to take his herd of sheep and goats to the nearby mountains for grazing. He would take a stick with him to control his herd. The stick had a small piece of iron attached at one end. One day he was surprised to find that he had to pull hard to free his stick from a rock on the mountainside. It seemed as if the stick was being attracted by the rock. The rock was a natural magnet and it attracted the iron tip of the shepherd’s stick. It is said that this is how natural magnets was discovered. Such rocks were given the name magnetite, perhaps after the name of that shepherd.
Magnetite contains iron. Some people believe that magnetite was first discovered at a place called Magnesia. The substances having the property of attracting iron are now known as magnets. This is how the story goes.
In any case, people now have discovered that certain rocks have the property of attracting pieces of iron. They also found that small pieces of these rocks have some special properties. They named these naturally occurring materials magnets.

1. What do you mean by “magnetic materials” and “non-magnetic materials”? Give examples.
   The materials which get attracted towards a magnet are called magnetic materials. For example, iron, nickel or cobalt.
   The materials which are not attracted towards a magnet are non-magnetic materials. For example wood, plastic, leather etc.
2. Write two most important properties of magnet.
   First is, a freely suspended magnet always point in the north-south direction.
   Second is, like magnetic poles repel each other, unlike magnetic poles attract each other.
3. If we gently break a bar magnet from its centre, will two poles get free?
   No, the two pieces will act as individual magnet.

What safety measures will you follow to store horseshoe magnet?
Safety measures to follow while storing horseshoe magnets:

1. Always wear safety goggles while handling large magnets.
2. Always wear gloves while handling magnets to prevent pinching.
3. Children should never be allowed to play with “Neodymium” magnets.
4. Keep magnets at least 20 cm away from sensitive electronic and storage devices.

Rub a magnet in the sand or soil. Pull out the magnet. There some particles of sand or soil sticking to the magnet. Now, gently shake the magnet to remove the particles of sand or soil. Some particles still sticking to it. These might be small pieces of iron (iron filings) picked up from the soil.

1. Write something about compass which is used to find out the direction.
   With the help of compass, we can get direction at a place, known as the compass. A compass is usually a small box with a glass cover on it. A magnetized needle is pivoted inside the box, which can rotate freely. The compass also has a dial with directions marked on it. The compass is kept at the place where we wish to know the directions. Its needle indicates the north-south direction when it comes to rest. The compass is then rotated until the north and south marked on the dial are at the two ends of the needle. To identify the north-pole of the magnetic needle, it is usually painted in a different color.
2. You might have read many interesting stories about the uses of magnets. Write anyone.
   One such story is about an emperor in China named Hoang Ti. It is said that he had a chariot with a statue of a lady that could rotate in any direction. It had an extended arm as if it was showing the way. The statue had an interesting property. It would rest in such a position that its extended arm always pointed towards South. By looking at the extended arm of the statue, the Emperor was able to locate directions when he went to new places on his chariot.

• What will happen, if a bar magnet is immersed in a heap of iron filings and pulled out?
  We know that the maximum amount of iron fillings sticks on the two ends or two poles of the bar magnet. In another words, the amount of iron filings clinging to the north pole is almost equal to the south pole because in the magnet the strength of both the poles is same and some iron filings also stick to the middle part of the bar magnet.
• How can you show that unlike poles attract each other while like poles repel each other?
  ANSWER: Suspend a magnet on a stand with the help of string. Now, it rests in North to South direction. Take another magnet which has been marked north to south on it and bring north pole of this magnet near the north pole of the suspended magnet. You will find that the suspended magnet rotates and moves away showing that like poles repels each other. The same can be repeated by bringing South Pole of one magnet near south pole of suspended magnet.
  Now you must have found that during the above experiment, south pole comes towards north pole and vice versa. It can be repeated by bringing south pole near a north pole, and north pole near south pole of suspended magnet. You will find that unlike poles attract each other. And like poles repels each other.

1. Do magnetic poles exist separately like changes? Explain.
   Magnetic poles do not exist separately like positive and negative changes. This means, that it is not possible to isolate a North Pole of a magnet from its South Pole by cutting the magnet from the middle. Whenever a bar magnet is cut into two halves, we get two ‘new magnets’ each with its North and South poles. This will continue indefinitely even if extremely small piece of bar magnet and obtained. Thus, magnetic poles always exist in pairs.
2. Why is compass needle kept in a closed glass vessel?
   Compass needle is a small and thin magnet used to find the direction. If it is kept in open, it may deflect in any direction due to pressure exerted by air. So, to know right direction, it is kept covered by glass covering.
3. Where are the poles of a circular magnet? How will you find this?
   Ring type or circular magnet also has two poles. Its exterior and interior parts act like different poles. To find out the nature of the two poles, we suspend circular magnet with a piece of thread. We bring another magnet near it. Both attract each other. It clearly concludes. Circular magnet that one surface of the circular magnet is attracted but the other surface is repelled by the same pole of the other magnet.

Magnetic Field: The region around the magnet where its magnetic influence can be felt is called the magnetic field of the magnet.
MRI: Magnetic Resonance Imaging (MRI) is a medical diagnostic technique which uses the magnetic field inside the body for obtaining images of different parts of the body.

• Define “attractive” and “directive” properties of a magnet.
  Attractive Property: A magnet has the property of attract some substance like Iron, Cobalt and Nickel when brought near it. This property of magnet is called the attractive property.
  Directive Property: If we suspend a magnet freely with thread, then it always aligns itself in the geographic north to south direction, when it comes to rest. This is called the directive property of a magnet.
• Suggest an arrangement to store a U-shaped magnet. How is this different from storing a pair of bar magnets?
  (i). Arrangement to store a U-shaped magnet: One metal plate is placed across the two poles of the U-shaped magnet to store it.
  (ii). Arrangement to store a Bar magnet: Bar magnets should be kept in pairs with their unlike poles on the same side. They must be separated by a piece of wood while two pieces of soft iron should be placed across their ends.

Suggest an activity to prepare a magnetic compass by using iron needle and a bar magnet.
Steps involved in preparing a magnetic compass are:

1. Take an iron needle which is to be magnetised.
2. Magnetise it using a bar magnet.
3. Insert the magnetised needle through a small piece of cork.
4. Let the cork float in a water in a bowl. Make sure that the needle does not touch the water.
5. Your magnetic compass is now ready to work. Note, the direction in which the needle points when the cork is floating.
6. Rotate the cork, with the needle fixed in it, in different directions. Note, the direction in which the needle points when the cork begins to float again without rotating.
7. You will observe that the needle indicates the North-South direction when it comes to rest.

How is a magnet demagnetized? A bar magnet is cut into two pieces A and B from the middle as shown in figure in the two pieces act as individual magnets mark the poles of these two pieces suggest an activity to verify your answer.
A magnet can be demagnetized, by heating and by hammering the magnet violently.
Yes, the two pieces will work as individual magnets because a mono-pole (single pole) of magnet never exists.
Activity:

1. Place the magnet, so formed (A and B) on the table.
2. Bring the North pole of both magnets towards each other, they will be repelled.
3. Bring the North and South Pole of both magnets towards each other, they will attract.
4. This proves that the two pieces will act as individual magnets having attraction and repulsion properties.

Steps involved in magnetising an iron strip are:

1. Take an iron strip which is to be magnetised.
2. Keep it on a wooden table.
3. Hold one end of a bar magnet in your hand and keep the other end of bar magnet near one edge of iron strip.
4. Without lifting, move it along the length of iron strip till you reach the other edge.
5. After reaching the end of iron strip, lift the bar magnet and bring it to the same position and repeat the process again and again.
6. Bring some iron fillings near the iron strip to check whether it has become a magnet. If not, continue the same process for some more time.

Three identical iron bars are kept on a table. Two out of three bars are magnets. In one of the magnets the North-South poles are marked. How will you find out which of the other two bars is a magnet? Identify the poles of this magnet.
To find out the magnet:

• (i)  Take the bar magnet with known poles in your hand.
• (ii)  Take one of the other two iron bars in other hand.
• (iii) Bring one side of iron bar towards the South Pole of the bar magnet and note down whether it is attracted or repelled.
• (iv) Bring other side of iron bar towards the South Pole of the bar magnet and again note down the same thing.
• (v) if there is an attraction in both cases (iii) and (iv), then it is definitely a simple iron bar.
• (vi) If there is an attraction in one case and repulsion in other case, then it is a bar magnet.
• (vii) Do the same for the third iron bar.
• To find out the poles:
  If in case (iii), the bar is attracted, then it is North Pole of the identified bar magnet. If the bar is repelled, then it is obviously a South Pole of the identified bar magnet.

Earth behaves like a huge bar magnet, with poles at its ends. The north pole point of this bar magnet approximately towards the geographical South Pole and its south pole points approximately towards the geographical North Pole. The north pole of a freely suspended magnet points towards the geographical north pole because it is attracted by the earth’s magnetic South Pole and the south pole of a freely suspended magnet points towards the geographical South Pole because it is attracted by the Earth’s magnetic North Pole. Hence, the freely suspended magnet always aligns itself in a north-south direction.