MAGNETS
                                                      Fun with Magnets

1.        Magnet : A magnet is a metallic object which attracts iron made or magnetic things.

2.       
Magnetite :An ore of iron which has magnetic properties.

3.       
Natural magnet : Magnetite is called natural magnet.

4.       
Uses of a magnet : A magnet finds its use at a number of places. For example, refrigerator’s door, some pencil boxes, many toys, magnetic stickers, soap stand, pin stand, all make use of a magnet for their functioning.


5.       
Shapes of magnets :Magnets are made of different materials and in different shapes.

 
6.        Effect of a magnet on materials :A magnet attracts certain materials whereas some do not get attracted towards magnet.

7.       
Magnetic materials :The materials which get attracted towards the magnet are known as magnetic e.g., iron, nickel, cobalt.

8.       
Non-magnetic materials :The materials which are not attracted towards the magnet are known as non-magnetic e.g., leather, plastic, cloth, paper.

9.       
Magnetic poles :Magnetic attraction is maximum near the ends of the magnet. These ends are called magnetic poles.
 
 

10.    
When suspended freely, magnet always aligns in north-south (N-S) direction.

11.    
North pole : When suspended freely, one pole of the magnet always points towards north. This is known as north-pole.

12.    
South pole : When suspended freely, the end of a magnet which points towards south is known as south-pole.

13.    
Lode stone : It was a stone indicating the direction used by sailors in olden days to identify directions when they were in sea.

14.    
Compass : This is a small glass case containing a magnetized needle pivoted on a nail. The needle can rotate freely. Wherever it is kept, its needle always rests in north-south direction. Normally the north-pole of the needle is pained red or some other indication is given to identify north and south-poles. So using this needle, north and south can be identified.

 

15.    
Attraction between two poles : Opposite poles of two magnets attract each other. It is called attraction.

16.    
Repulsion between two poles : Similar poles of two magnets repel each other. It is called repulsion.
 
 
17.     Magnetic effect can pass through screen : Magnetic influence can pass through screens of some substances like cloth, plastic, paper, glass, etc.

18.    
Magnet lose their properties if they are heated, hammered or dropped strongly and hardly.

19.     To keep them safe 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. For horse-shoe magnet, one should keep a piece of iron across the poles.

Q.1. Fill in the blanks in the following :

(i)           
Artificial magnets are made in different shapes such as ………. , ……… and …………. .
(ii)          The materials which are attracted towards a magnet are called ……….. .
(iii)         Paper is not a ………… material.
(iv)         In olden days, sailors used to find direction by suspending a piece of ……….. .
(v)          A magnet always has ………… poles.

Ans.
(i)   bar shaped, U-shaped, circular
         (ii)  magnetic
         (iii) magnetic
         (iv) lode stone
         (v)  two

Q.2. State whether the following statements are True or False :

(i)        A cylindrical magnet has only one pole.
(ii)      Artificial magnets were discovered in Greece.
(iii)     Similar poles of a magnet repel each other.
(iv)     Maximum iron filings stick in the middle of a bar magnet when it is brought near them.
(v)      Bar magnets always point towards North-South direction.
(vi)     A compass can be used to find East-West direction at any place.

Ans.
 (i) False         (ii) True               (iii) True               (iv) False
          (v) True         (vi) False             (vii) False.

Q.3. It was observed that a pencil sharpener gets attracted by both the poles of a magnet although its body is made of plastic. Name a material that might have been used to make some part of it.

Ans. A pencil sharpener gets attracted by both the poles of a magnet although its body is made of plastic, because the pencil sharpener contains some iron particles.

Q.4. Column I shows different positions in which one pole of a magnet is placed near that of the other. Column II indicates the resulting action between them for each situation. Fill in the blanks.

Column IColumn II

N – N

…………
N - …Attraction

S – N…………

… - SRepulsion

  
Ans.
Column IColumn II

N – N

Repulsion
N – SAttraction

S – NAttraction

S - SRepulsion

 
Q.5. Write any two properties of a magnet.

Ans.
(i)  Magnet attracts magnetic substances.
         (ii) Magnet when freely suspended always points in north-south direction.

Q.6. Where are poles of a bar magnet located?


Ans.
At the end.
When a bar magnet is placed near some iron fillings. We observe more iron fillings clinging to the magnet near its end. 

The ends of a magnet where maximum iron fillings get clung i.e., the attraction is strongest, are known as poles.

Q.7. A bar magnet has no markings to indicate its poles. How would you find out near which end is its north pole located?

Ans. When a bar magnet is suspended freely, it always rests in north-south direction. The end pointing towards north is called north seeking end or the north-pole and the end pointing towards south is called south seeking end or the south-pole of the magnet. Usually, north (N) and south (S) poles are marked on the magnets .

Q.8. You are given an iron strip. How will you make it into a magnet?


Ans.
We can convert an iron strip by repeatedly closing it by a bar magnet systematically. Take the iron strip. Closes it with one pole of a bar magnet in one direction. When you reach the other end of the iron piece not lift the magnet and bring the same pole back to the starting end of the iron piece. Stroke again, in the same direction. Repeat this process about 30-40 times. Check whether the iron piece has now become a magnet. If not, continue the process for some more time. Remember the pole of the magnet and the direction of stroking is not to be changed. In the same way, iron needle can also be converted into a magnet.


Q.9. How is a Magnetic compass used to find directions?


Ans.
Magnetic compass is a small magnetic needle enclosed in a glass case. The magnetic needle is fixed at the centre so that it can move freely. When kept on a table top, the needle of the compass will come to rest pointing in the north-south direction. It is thus used in the laboratory to mark direction. 

Q.10. A magnet was brought from different directions towards a toy boat that has been floating in water in a tub. Affect observed in each case is stated in Column I. Possible reasons for the observed affects are mentioned in Column II. Match the statements given in Column I with those in Column II.

Column IColumn II

Boat gets attracted towards the magnetBoat is fitted with a magnet with north pole towards its head

Boat is not affected by the magnetBoat is fitted with a magnet with south pole towards its head

Boat moves towards the magnet if north pole of the magnet is brought near its headBoat has a small magnet fixed along its length
 

Boat moves away from the magnet when north pole is brought near its head

Boat is made of magnetic material
Boat floats without changing its directionBoat is made up non-magnetic material
 
Ans.
 
Column IColumn II

Boat gets attracted towards the magnetBoat is made of magnetic material

Boat is not affected by the magnetBoat is made up non-magnetic material

Boat moves towards the magnet if north pole of the magnet is brought near its headBoat is fitted with a magnet with south pole towards its head

Boat moves away from the magnet when north pole is brought near its head

Boat is fitted with a magnet with north pole towards its head

Boat floats without changing its directionBoat has a small magnet fixed along its length
 


ADDITIONAL IMPORTANT QUESTIONS

Q.1. What is a magnet?


Ans.
It is a material which has the property of attracting pieces of iron towards it.

Q.2. What are properties of magnets?


Ans.
(i)   It attracts iron pieces towards itself.
        (ii)   It always aligns itself in the same direction, if left to rotate freely.
        (iii)  It is composed of oxides of iron (Fe3O4).

Q.3. What is magnetite called now?


Ans.
Magnetite like materials are called magnets now.

Q.4. In which direction does freely suspended magnet rests?


Ans.
A freely suspended magnet always points in the north-south direction.

Q.5. Which is the north-pole of a bar magnet?


Ans.
It is the tip of a bar magnet which points towards the north direction.

Q.6. Which is the south-pole of a bar magnet?


Ans.
It is the tip of a bar magnet which points towards the north direction.

Q.7. When was magnetite discovered?


Ans.
It was discovered around 800 B.C.

Q.8. How do the shipmen find the direction even when north pointing pole star is not visible?


Ans.
Shipmen during navigation can find the direction with the help of magnetic needle. This is believed to be first used by Chinese.

Q.9. Why does bar magnet always points in north-south direction?


Ans.
Bar magnet always points in north-south direction when left freely suspended because earth itself behaves like a magnet and north-pole of bar magnet is attracted towards south-pole of earth’s magnet and vice versa.

Q.10. Where are south and north poles of earth’s magnet?


Ans.
Earth’s magnetic south-pole is near the geographic north-pole and north-pole of earth’s magnet is near geographic south-pole.

Q.11. Who discovered magnet?


Ans.
An old shepherd lived on Create Island named Magnes discovered it.

Q.12. Name the first magnet.


Ans.
Lodestone.

Q.13. What is lodestone?


Ans.
Lodestone is a type of iron. It bears the properties of magnet.

Q.14. Write the name of some non-magnetic substance.


Ans.
Rubber, Cotton, Plastic, Wood, Button, Cloth.

Q.15. Name the country in which it (magnet) was discovered.


Ans.
Greece.

Q.16. What happens when similar poles come close to each other?


Ans.
They repel each other.

Q.17. When do two magnets attract each other?


Ans.
Two magnets attract each other when their unlike (opposite) poles come close to each other.

Q.18. In which direction does a freely hanging (suspended) magnet indicate?


Ans.
It indicates (points) towards north-south direction.

Q.19. Can an ordinary vessel (lota) be magnetized?


Ans.
Yes, to magnetise ordinary vessel, it would have to be buried in the earth for many years.

Q.20. Make a list of given substances into two groups – Magnetic and non-magnetic.


  Key, Wood, Glass, Alpin, Chalk, Pencil, Nail, Cup of tea, Book, Rubber, Niddle, Fork.

Ans.

Magnetic SubstancesNon-magnetic Substances

Key, Alpin, Nail, Needle, Fork
(because all these stick to the magnet)
Wood, Glass, Chalk, Pencil, Cup of tea, Book, Rubber.
(None of these sticks to the magnet.)

Q.21. How many poles are there in a magnet?


Ans.
There are two poles in a magnet north-pole and south-pole. See Fig. 13.2.

Q.22. To which part of the magnet do the most of the iron fillings (or pins) stick?


Ans.
Most of the iron filings (or pins) stick to the poles i.e. north and south poles. At these poles of magnet, magnetic effect is maximum.

Q.23. To which part of the magnet do none or only a few iron filings (or pins) stick?


Ans.
Minimum number of iron filings stick to the middle part of the magnet. Magnet has its magnetic effect least in this part (middle part).

Q.24. Are both poles of a magnet similar?


Ans.
No, the two poles of a magnet are not similar (alike). Both have different tendency. The pole that points towards the north is called north-pole while the pole pointing always towards the south is called south-pole.

Q.25. Does the compass needle point in different direction?


Ans.
The compass needle has a magnetic needle closed in a glass covering. The needle can rotate on its pin pointed base. Its red marked end always indicates towards the north direction. It always rests in north-south direction. We use it to find out the direction. (See Fig. 13.5)

Q.26. Fill in the blanks :

(i)        When a suspended magnet comes to rest, one pole always points towards the ………… .
(ii)      And the other pole always points towards the ………… .

Ans.
(i) North              (ii) South.

Q.27. Make a boat (paper boat). Insert four pins in its base. Now float the boat in water filled container (vessel). Try to move the boat with the help of a magnet held outside the container. Find out how the boat is driven?


Ans.
The paper boat is driven by the force of attraction because pins, made of irons are attracted by the magnet.

Q.28. Write the uses of magnets.


Ans.
Uses of magnets :
(i)        Magnet is used to separate iron from any mixture.
(ii)      It is used by sailors and pilots to know the direction.
(iii)     During fog or storm it is used to know the right direction to move.


Q.29. How do the ragpickers (kabari wale) collect iron things from dust and waste materials?


Ans.
Ragpickers carry a piece of magnet with them. Whenever they feel there may be iron pieces they bring the magnet near the heap of wastes of the iron pieces. If these are present, they will stick to the magnet.

Q.30. How did we know that magnet is helpful to find (detect) directions?


Ans.
About 800 years ago, Chinese saw that a hanging lodestone always comes to rest in a particular direction i.e., north-south. Therefore they came to know about the direction with the help of lodestone.

Q.31. Why is compass needle kept in a closed glass vessel?


Ans.
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.

Q.32. Your mother was stitching your shirt. The needle slipped from her hand into a box containing buttons, threads etc. How would you search for the needle?


Ans.
We can search the needle with the help of a bar magnet. Because needle is made up of iron it will stick to the bar magnet.

Q.33. What happens when the north-pole of a magnet is brought near (i) north-pole, (ii) the south-pole of a freely suspended magnet?


Ans.
(i) North-pole of the suspended magnet will move away.
         (ii) South-pole of the suspended magnet will get attracted towards it.

Q.34. Can we isolate north-pole or south-pole?


Ans.
No, we cannot isolate north-pole of a magnet from its south-pole or vice versa. If you break a bar magnet into two halves, you will not get a single north or south pole but two magnets each with its north and south-poles.

Q.35. What will happen to the magnet when we cut it into two pieces?


Ans.
When we cut a bar magnet into two pieces both these pieces act as magnets and we get two magnet .

Q.36. What is a permanent magnet?

Ans. A permanent magnet is one which has magnetic properties even without the presence of another magnet. In permanent magnets, the alignment of domains lasts for a longer duration.

Q.37. How do the properties of a permanent magnet get destroyed?


Ans.
(i)    By hammering magnet violently.
         (ii)   By heating a magnet strongly.
         (iii)  By improper handling and storage.

Q.38. Do magnetic poles exist separately like charges? Explain.


Ans.
Magnetic poles do not exist separately like positive and negative charges. 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. When over a bar magnet is cut into two halves, we get two new magnets, each with its north and south pole. This will continue indefinitely even if extremely small pieces of bar magnets are obtained. Thus magnetic poles always exist in pairs.

Q.39. What happens when a pole of a bar magnet say its north-pole is marked with a chalk and suspended freely? What do you observe on rotating the bar magnet?


Ans.
The marked pole comes to rest in north direction. On rotating, after sometime it comes again to rest in north direction.

Q.40. One feels a pull while opening or closing the door of a refrigerator. What can be the possible reason?


Ans.
The door of refrigerator has a magnet. When the door of a refrigerator is closed, the refrigerator attracts the iron door we have to apply some force to open the door so that magnet gets separated.


Q.41. How do the counters in a ludo game stick to its iron board?


Ans.
Ludo board is made of iron, counters are fitted with magnet. The counters stick with board without going anywhere. It is due to magnetic effect.

Q.42. Why is there a circular magnet near the mouth of some pin holders?


Ans.
There is a circular magnet near the mouth of some pin holders. In the presence of magnet, pins are attracted at the mouth of pin holder as we pick a pin from pin holder, magnetic effect does not remain more and the pin comes out. Rest of the pins remain inside the pin box.


Q.43. When a bar magnet was brought close to a compass, the orientation of the needle became as shown in figure. Identify the poles on the ends of the bar magnet marked ‘A’ and ‘B’. Explain how you arrived at your answer.


Ans.
Orientation of the needle clearly  shows that red marked end (north-pole) attract the end of bar magnet marked “A”. It means both these are unlike poles and the end of bar magnet marked “A” is south-pole. End marked ‘B’ is north pole because like (same) poles repel each other.


Q.44. Bhawana witnessed on interesting game at the fair. A duck was floating in a tub. When a plate containing some grains of rice was brought close to the duck, the duck moved towards the plate. But, when a plate containing some pebbles was brought close to the duck, it moved away from the plate. Explain how this could have been possible.


Ans.
This game is based on the plate containing rice may have magnet attached to its bottom. The magnet is fitted in such way that its north-pole points towards rice grains, while south-pole indicate towards pebbles. A magnet (bar magnet) may also be fitted in the bottom of the duck, where south-pole points towards mouth and north-pole towards tail of the duck.
When the rice portion of the plate is brought closer to the duck, the duck moves towards rice grains because unlike poles of two magnets attract each other. In second situations, same (like) poles repel each other. So the duck moves away.

 Q.45. Hang a bar magnet with a thread on a stand and rotate the base of stand. What will happen?
Ans. The direction of bar magnet is not changed as we rotate the stand. It is because a freely suspended magnet comes to rest in particular direction i.e., north-south direction. In this activity only stand changes its direction.

Q.46. Where are the poles of a circular magnet? How will you find this?

Ans. 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 to it. Both attract each other. It clearly concludes that one surface of the circular magnet is attracted but the other surface is repelled by the same pole of the other magnet.

Q.47. Mark the north-poles of two bar magnet and bring the poles of the magnet near each other, and note down your observations in table.


Ans.

Poles of facing one anotherThey are calledWe observe

North-South
 
North-North
 
South-South
 
South-North
Opposite poles
 
Similar poles
 
Similar poles
 
Opposite poles
Attraction
 
Repulsion
 
Repulsion
 
Attraction
 
Q.48. Can a magnet be demagnetized? How?

Ans.
Yes, A magnet can be demagnetized :
(i)            By packing like poles of two magnets in same direction.
(ii)          By hammering the magnet hard.
(iii)         By heating the magnet strongly.

Q.49. How should two-bar magnets be kept?


Ans.
After using it, two bar magnets should be placed inside a wooden box so that :
(i)            The poles of two magnets lie opposite to each other.
(ii)          A wooden piece should be kept between the two magnet.
(iii)         Metallic caps should be put on the poles, otherwise they will  attract other magnetic objects.


Q.50. How was magnet discovered?

Ans. It is said  that once upon a time, in Greece, there lived a shepherd. His name was Magnes. He used to take his herd of sheep and goats to the nearby mountains for grazing. He used to carry a stick with iron tip at one end. One day he rested the iron mounted end of the stick on a stone. As soon as the stick touched it, the stone got clung to it. The stone was a natural magnet and it attracted the iron tip of the shepherd’s stick. This was how natural magnet was discovered. Perhaps on the name of that shepherd, that stone was given the name magnetite and hence the name magnet to the substances having such property.   

Q.51. How can you show that unlike poles attract each other while like poles repel each other?

Ans. Suspend a magnet on a stand with the help of a string. Now it rests in N-S direction. Take another magnet which have marked N-S on it and bring N-pole of this magnet near the N-pole of the suspended magnet. You will find that the suspended magnet rotates and moves away showing that like poles repel 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.
 

OBJECTIVE TYPE QUESTIONS
Q.1. Match the following items given in Column A with that in Column B :
Column AColumn B

(a)  Magnetite
 
(b)  Iron, Nickel, Cobalt
 
(c)  Leather, plastic, wax
 
(d)  Lode stone
 
(e)  Compass
 
(f)   Like poles of two magnets
 
(g)  Opposite poles of two magnets
 
(h)  Magnus
(i)      Non-magnetic substances.
 
   (ii)   Used to find out N-S direction.
 
   (iii)  Attract each other
 
   (iv)  Natural magnet
 
   (v)   Repel each other
 
   (vi)  Discovered magnet incidently
 
   (vii) Magnetic substance
 
   (viii) Name of first magnet
 
Q.2. Fill in the blanks with appropriate words :
(a)  When north-pole of one magnet is brought near the …………. of another magnet, they attract one another.
(b)  When the north-pole of one magnet is brought close to the ………… of another magnet, they repel each other.
(c)  Similar poles of two magnets …………. one another.
(d)  A compass needle always points in a …………. Direction.
(e)  Strickers with pieces of magnet inside them easily stick to ………… surfaces like the doors of refrigerator.
(f)   Materials which get …………. towards magnet are known as magnetic.
(g)  The ………… of magnet where maximum iron fillings get clung, are known as ………… .
(h)  Magnetic effect can pass through ……….. .
(i)    We should not drop the magnet, don’t heat it, don’t …………. It.
(j)    The south pole of the earth’s magnet is near the geographical ………… pole.
(k)  Magnetic poles always …………. In pairs.
(l)    Hammering destroys the ………….. of small magnets inside.


Q.3. State whether the statements given below are True or False :

(i)        Lodestone is composed of oxides of iron.
(ii)      North and south poles are found to exist separately.
(iii)     Magnetite doesn’t show magnetic properties.
(iv)     If we cut a bar magnet in two halves we will have two magnets.
(v)      Heat can destroy magnetic properties of a magnet.
(vi)     Magnets are made up of different materials and in different shapes.
(vii)   Compass needle is made of a magnet.
(viii)  There is a maximum attraction in middle of a bar magnet.

Q.4. Choose the correct option in the following questions :


(i)       
Which is an example of a magnetic substance?

(a)  Iron                                          (b) Nickel
(c) Cobalt                                           (d) All of these

(ii)     
Magnets have a shape

(a)  cylindrical                                    (b) ball ended
(c) horse shoe                                  (d) all of these

(iii)    
When a bar magnet is brought near iron dust most of the dust sticks

(a)  near the middle                          (b) equally everywhere
(c) near two ends                             (d) at the middle and ends

(iv)    
A freely suspended bar magnet rests in

(a)  north-south direction                 (b) east-west direction
(c) upside down                               (d) any direction by chance

(v)     
Attraction is seen between the poles of two bar magnets in the case of

(a)  N-pole of one magnet with N-pole of other
(b)  N-pole of one magnet with S-pole of other
(c)  S-pole of one magnet with s-pole of other
(d)  All of these cases will show attraction

(vi)    
Which is natural magnet?

(a)  Magnetite                                    (b) Haemetite
(c) Bakelite                                        (d) Copper

(vii)  
Choose the wrong statement :

(a)  Bar magnets are kept in pairs with their unlike poles on the same side
(b)  Magnets should be kept away from electronic devices
(c)  Magnets lose their property by oiling
(d)  All of these

(viii) 
The magnetic properties of a magnet cannot be destroyed by

(a)  hammering                                  (b) heating
(c) dropping on a hard surface      (d) boiling

(ix)    
When two ends of a magnet the magnetic force is maximum are called

(a)  north pole                                    (b) south pole
(c) magnetic pole                             (d) self demagnetization

(x)     
Magnets attract

(a)  wood                                            (b) plastic
(c) paper                                            (d) iron
 
ANSWERS TO OBJECTIVE TYPE QUESTIONS

Q.1. Match the following items given in Column A with that in Column B :

Column AColumn B

(a)  Magnetite
 
(b)  Iron, Nickel, Cobalt
 
(c)  Leather, plastic, wax
 
(d)  Lode stone
 
(e)  Compass
 
(f)   Like poles of two magnets
 
(g)  Opposite poles of two magnets
 
(h)  Magnus
(iv)   Natural magnet
 
(vii) Magnetic substance
 
 (i) Non-magnetic substances.
 
(viii) Name of first magnet
 
 (ii)  Used to find out N-S direction.
 
 (v) Repel each other
 
(iii) Attract each other
 
 (vi)Discovered magnet incidently

 
Q.2. Fill in the blanks :
        (a) south pole                 (b) north pole               (c) repel             (d) north-south
        (e) iron                            (f) attracted                  (g) ends, poles  (h) screen
        (i) hammer                      (j) north                        (k) exist              (l) magnetism.

Q.3. True/False :

        (i) True                        (ii) False                     (iii) False                  (iv) True
        (v) True                       (vi) True                      (vii) True                  (viii) False.

Q.4. Choose the correct option :

(i)        (d) All of these are attracted towards a magnet.
(ii)      (d) Magnets may be various shapes including bar magnets.
(iii)     (c) Magnetic field intensity is maximum at the poles of a bar magnet.
(iv)     (a) A bar magnet always rests in N-S direction when suspended freely.
(v)      (b) Unlike poles attract and like poles repel each other.
(vi)     (a) Magnetite is a natural magnet.
(vii)    (d) Magnet does not lose their property by oiling.
(viii)  (d) Magnetic properties of a magnet cannot be destroyed by boiling, because magnetic properties destroyed by hammering, dropping on hard surface and by heating.
(ix)     (c) Magnetic poles (North pole and South pole)
(x)      (d) Iron attract with magnet.