Living Science Physics Class 6 ICSE Solutions Chapter 8 Magnetism

ICSE Living Science Physics for Class 6 Solutions Chapter 8 Magnetism

Check Your Progress (Page 88)

Answer the following.
Question 1.
What are magnetic substances ?
Answer:
Substances such as iron, nickel, cobalt, or their alloys that get attracted by a magnet are called magnetic substances.

Question 2.
What are artificial magnets ?
Answer:
Magnets that are made by humans from magnetic substances are called artificial magnets. They can be made in different shapes and sizes like bar magnet, horseshoe magnet, etc.

Question 3.
Why is it not possible to isolate a single magnetic pole?
Answer:
Magnetic poles always exist in pairs and cannot exist independently. If a bar magnet is broken into two or more pieces, each of them will have a north pole and a southpole. Hence, it is impossible to obtain a piece of magnet with only one magnetic pole.

Question 4.
Can you bring two similar poles of two different magnetic close together easily ? Why ?
Answer:
No, because like poles repel each other, when two magnetic are brought close to each other.

Question 5.
What is meant by the directional property of magnets ?
Answer:
Directional property of magnets states that a freely suspended magnet always points towards the geographical north-south direction. Eveiy magnet, irrespective of its shape, has a north pole and a south pole.

A. Tick the most appropriate answer.

Question 1.
Temporary magnets are made of –
a. soft iron
b. steel
c. stainless steel
d. copper
Answer:
a. soft iron

Question 2.
The surest test of magnetism is –
a. attraction
b. repulsion –
c. diffusion
d. hammering
Answer:
b. repulsion

Question 3.
Which of the following methods is used to magnetize a magnetic without touching it by a magnet ?
a. Single-touch
b. Double-touch
c. Using electric current
d. None of these
Answer:
c. Using electric current

Question 4.
The region around a magnet where its magnetic force ‘ can be experienced is called –
a. magnetic axis
b. magnetic equator
c. magnetic field
d. magnetic poles
Answer:
c. magnetic field

Question 5.
A permanent magnet can be demagnetized by –
a. hammering
b. heating
c. rough handling
d. all of these.
Answer:
d. all of these

B. Fill in the blanks.

Question 1.
A freely suspended magnet always comes to rest in the …………… direction.
Answer:
A freely suspended magnet always comes to rest in the north – south direction.

Question 2.
Permanent magnets are generally made of steel, cobalt, nickel, or an alloy called ………….
Answer:
Permanent magnets are generally made of steel, cobalt, nickel, or an alloy called ALNICO.

Question 3.
The perpendicular bisector of the line joining the two poles of a magnet is called ………….
Answer:
The perpendicular bisector of the line joining the two poles of a magnet is called magnetic equator.

Question 4.
The north pole of the imaginary magnet of the earth is ” near the geographic ……………. pole.
Answer:
The north pole of the imaginary magnet of the earth is near the geographic south pole.

Question 5.
Magnetic poles always exist in
Answer:
Magnetic poles always exist in pairs.

C. State if the following statements are true or false. Correct the statement if it is false.

Question 1.
If a bar magnet is cut in two pieces, then one piece will have only the north pole and the other will have only the south pole.
Answer:
False. If a bar magnet is cut in two pieces, then each of the piece will have the north pole and the south pole.

Question 2.
Attraction is the surest test for magnetism.
Answer:
False. Repulsion is the surest test for magnetism;

Question 3.
Temporary magnets are made of cobalt.
Answer:
False. Temporaiy magnets are made of soft iron.. –

Question 4.
As we move away from a magnet, its attraction power weakens.
Answer:
True.

Question 5.
Whenever a magnet is not in use, it should be stored along with other magnets.
Answer:
False. Whenever a magnet is not in use, it should not be stored along with other magnets.

D. Give reasons for the following.

Question 1.
Magnets must be handled with care.
Answer:
Magnets must be handled with care or else they lose their magnetic properties and become weak. To prevent a magnet from becoming demagnetized, magnet should not be handled roughly, hammered, dropped, heated. It should be stored using magnetic keepers.

Question 2.
Iron is a magnetic substance.
Answer:
Iron is a magnetic substance because it gets attracted by a magnet.

Question 3.
The directive property of magnets is used in a compass.
Answer:
The directive property of magnet is used in a compass for navigation purposes as the magnetic needle inside the compass always rests in the geographical north-south direction.

Question 4.
Electromagnets are temporary magnets.
Answer:
An electromagnet is a temporary magnet because it behaves like a magnet only till the current is passed through it. When the current is stopped, it stops behaving like a magnet.

Question 5.
Magnets are used to close the doors of a refrigerator tightly.
Answer:
Because of the attractive property of a magnet. A magnet attracts magnetic substances by exerting a force called magnetic force. This keeps the door of a refrigerator closed tightly.

E. Answer the following in short.

Question 1.
Give two examples each of magnetic and non-magnetic substances.
Answer:
Examples of magnetic substances – Iron, nickel, cobalt Examples of non-magnetic substances – Plastic, wool, wood, paper, rubber, etc.

Question 2.
What is a magnet ? Differentiate between natural and artificial magnets.
Answer:
A magnet is a piece of metal that can attract metals such as iron, cobalt and nickel. Naturally occurring rocks such as Lodestone or magnetite have the ability of attracting magnetic substances and hence are called natural magnets.
Magnets that are made by man from magnetic substances are called artificial magnets. These come in different shapes such as bar magnets, horse shoe magnets, disc magnets and ring magnets. Artificial magnets can be made in any size, shape or strength as desired but natural magnets cannot be made as desired.

Question 3.
If a bar magnet is placed over iron fillings, where will the attraction of the iron fillings be –
a. maximum ?
b. minimum ?
Answer:
a. At the ends of the bar magnet.
b. At the centre of the magnet.

Question 4.
Define the following terms regarding a bar magnet,
a. Magnetic axis
b. Effective length
c. Magnetic equator
d. Magnetic field
Answer:

a. An imaginary line (XY) passing through the magnetic north pole and magnetic south pole of a bar magnet is called its magnetic axis.
b. The distance (NS) between the north pole and south pole of a magnet is called the length or effective length of the magnet.
c. An imaginary line (PQ) bisecting the effective length of a magnet is called the magnetic equator of the magnet.
d. The region around a magnet where its magnetic force can be experienced is called the magnetic field.

Question 5.
How will you test if a given substance is a magnet or not?
Answer:
Aim : To test whether a metallic bar is a magnet or not. Materials Required : An unidentified metallic bar and a bar magnet.
Procedure : Keep the unidentified metallic bar on a wooden table. Take a bar magnet and bring one of its poles close to one end of the metallic bar.
Observation and Conclusion :
1. If the bar is not attracted to the magnet, it means that the bar is made up of a non-magnetic material. So, it is definitely not a magnet.
2. If the bar is repelled by the magnet, it is definitely a magnet (fig- a)
3. If the bar is attracted to the magnet (fig. b), it may either be:
a. made of a magnetic material, or
b. a magnet that has its opposite pole facing the magnet. So, it requires further investigation.
Now bring the other pole of the magnet near the same end of the metallic bar.
4. If the bar is again attracted to the magnet (fig. c), it means that the metallic bar does not have magnetic poles. Hence, it is not a magnet.

5. If the bar is repelled by the magnet (fig. d), it clearly shows that this end of the bar has the same pole as the end of the magnet facing it (like poles repel). Hence, the metallic bar is a magnet. Thus, repulsion is the surest test for magnetism.

Question 6.
Name a few common appliances that use electromagnets.
Answer:
Electric bells, electric motor, telephones, loudspeakers and generators are few common appliances that use electromagnets.

F. Answer the following in detail.

Question 1.
Distinguish between a temporary magnet and a permanent magnet.
Answer:
Temporary magnet:

• These magnets retain their magnetic property for a short duration of time.
• These are made of soft iron.
• They lose their magnetic properties once the magnetizing force is removed.

Permanent magnet:

• These magnets retain their magnetic property always.
• These are made of iron, steel, iron. cobalt, nickel or an alloy called ANILCO.
• They retain their magnetic properties even after the magnetizing force is remov ed.

Question 2.
Write a short note on the theory of magnetism.
Answer:
All substances are made of minute particles. In a magnetic substance whether magnetized or non-magnetized), each individual particle behaves like an independent magnet. In the unmagnetized state, these particles within the substance are present in a random fashion such that they cancel out the magnetic effects of each other.

In a magnetized state, these particles align in a particle direction and the substance behaves like a magnet.

Question 3.
List four methods of magnetizing a magnetic substance.
Answer:
Methods of magnetizing a magnetic material are :
1. Single-touch method – A magnet is rubbed along the magnetic substance from one end to another.

2. Double-touch method – Opposite poles of two magnets are placed next to each other at the centre of the magnetic substance and rubbed in opposite direction along it.

3. Magnetizing by induction – It is a method to make temporary magnets under the influence of a magnetizing force. The magnetic properties disappear when the influence of the magnetizing force is removed. (A permanent magnet is brought close to the magnetic substance but not touched.)

4. Electric current – A magnet made by using electric current is called an electromagnet. It is a temporary magnet and stops behaving like a magnet when the current is stopped. Electromagnets can become permanent magnets if certain
materials like steel and special alloys are placed in a coil and very strong current is passed through the coil.

Question 4.
How is the single-touch method of magnetism different from the double-touch method ?
Answer:
Single-touch method of magnetism:
1. A magnet is rubbed along the magnetic substance (needle or iron piece) from one end to another and lifted vertically upwards.

Double-touch method of magnetism :
1. Opposite poles of two magnets are placed next to each other at the centre of the magnetic substance and rubbed in opposite direction.

Question 5.
How can you make an electromagnet ? State the characteristics of an electromagnet.
Answer:
Aim : To make an electromagnet.
Materials Required : An iron nail, a battery, a switch, some insulated copper wire and some iron paper pins.
Procedure : Coil the insulated copper wire around the iron nail. Connect the ends of the wire to the battery through the switch. Close the switch so that electric current flows through the copper wire. Now bring the iron paper pins close to the iron nail.
Observation And Conclusion : The paper pins get attracted to the nail, showing that the nail has turned into an electromagnet. Now, if you switch off the current, the iron paper pins will drop off the iron nail.

Question 6.
How can a magnet be demagnetized ?
Answer:
A magnet can be demagnetized in the following ways :

• rough handling
• hammering the magnet several times.
• passing an alternating current around the magnet.
• dropping the magnet on the floor several times.
• heating the magnet to a very high temperature.

G. Answer the following.

Question 1.
Gauri had a long bar magnet with her while she needed a U shaped magnet for her school project. She decided to heat her bar magnet and bend it to give it a U shape. Suggest Gauri where and why is she wrong. What will be the outcome if she does what she decided.
Answer:
If Gauri heats her bar magnet, it would get demagnetized and lose its magnetic properties.

Question 2.
Mr Raman wants to use a permanent magnet to get the backyard of his factory cleared of junk. How can you convince Mr Raman to use an electromagnet instead of a permanent one ? What will happen if he does not follow your advice ?
Answer:
We can control and change the magnetic force of the electromagnet by controlling the amount of electric current passed to it by an electric generator. When the power is on, the magnetic field (force) will attract the junk to it. When the junk is to be dropped somewhere, the power is cut to the electromagnet and the junk drops. If permanent magnet would be used, it would get difficult to detach the junk from it.

H. Draw diagrams of the following.

Question 1.
Draw a bar magnet and label magnetic poles, magnetic axis, magnetic equator and the effective length on it.
Answer:

N → North pole
S → South pole
XY → Magnetic axis
PQ → Magnetic equator
NS → Effective length

Question 2.
Draw a diagram to show the magnetic field of earth. Mark the geographic north, geographic south, magnetic north and the magnetic south in your diagram.
Answer:

Living Science Physics Class 6 ICSE Solutions