6 magnetism - the assam valley school today/worksheets/6/magneti… · class-vi physics question...

1Class-VI Physics Question Bank

6 MAGNETISMI. Tick ( ) the most appropriate answer.

1. When a bar magnet is suspended freely, it comes to rest :(a) east-west direction (b) north-east direction(c) north-south direction (d) north-west direction

2. A bar magnet is cut into four pieces. Each piece is :(a) complete magnet (b) some pieces have only north pole(c) some pieces have only south pole(d) all pieces lose magnetism

3. A bar of steel can be permanently magnetised by :(a) rubbing a bar magnet with it along the length(b) rubbing a bar magnet at its ends(c) rubbing a bar magnet at its centre (d) none of these

4. Similar poles of bar magnets :(a) attract each other (b) repel each other(c) neither attract nor repel each other (d) none of these

5. Lodestone is an example of :(a) artificial magnet (b) electromagnet(c) natural magnet (d) none of these

6. An artificial magnet which is used for finding geographicaldirections is :(a) bar magnet (b) electromagnet(c) horseshoe magnet (d) magnetic compass

7. The surest test for magnetism is :(a) attraction (b) repulsion(c) both attraction and repulsion (d) none of these

8. Very strong magnets are :(a) natural magnets (b) permanent magnets(c) electromagnets (d) magnetic needle

9. Making a nail behave like a magnet by bringing a magnet nearit but not touching it is :(a) single-touch method (b) magnetic induction method(c) double-touch method (d) none of these

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10. The attraction of iron filings by the poles of a magnet is :(a) maximum (b) zero (c) medium (d) minimum

11. In a magnet :(a) north pole is stronger than south pole(b) south pole is stronger than north pole(c) both the poles are of equal strength(d) none of these

12. The earth behaves like a huge bar magnet with its magneticnorth pole situated near the :(a) geographical north pole (b) geographical west pole(c) geographical south pole (d) geographical east pole

13. Ferrite magnets are made up of a mixture of :(a) iron oxide and aluminium oxide(b) iron oxide and barium oxide(c) iron oxide and calcium oxide(d) potassium oxide and barium oxide

14. Which of the following is an example of a natural magnet?(a) Lodestone (b) Iron (c) Steel (d) Cbalt

15. Artificial magnet used in the laboratory to detect the directionis a :(a) horseshoe magnet (b) U-shaped magnet(c) bar magnet (d) magnetic needle

16. In an unmagnetized substance, the molecular magnet forms :(a) open chains (b) straight chains(c) closed chains (d) none of these

17. A permanent magnet :(a) attracts all substances (b) attract only magnetic substances(c) repels all substances (d) none of these

18. Which of the following is a magnetic substance?(a) Cobalt (b) Aluminium (c) Copper (d) Wood

19. Temporary magnets are made up of :(a) steel (b) copper (c) soft iron (d) aluminium

20. Permanent magnets are made up of :(a) steel (b) copper (c) soft iron (d) aluminium

21. Presence of magnetism in a magnet, is due to :(a) basic structural property


(b) due to molecular arrangement in the form of a closed chain(c) due to molecular arrangement in a particular order(d) none of these

22. Effective length of a magnet is :(a) equal to its geometric length(b) greater than its geometric length(c) smaller than its geometric length(d) either greater or smaller depending on the nature of the

material23. Which of the following is a non-magnetic substance?

(a) Iron (b) Steel (c) Nickel (d) CopperAns. 1. (c) 2. (a) 3. (a) 4. (b) 5. (c) 6. (d) 7. (b) 8. (c) 9. (b)

10. (a) 11. (a) 12. (c) 13. (a) 14. (a) 15. (d) 16. (c) 17. (b)18. (a) 19. (c) 20. (a) 21. (c) 22. (c) 23. (d).

II. Fill in the blank spaces using correct words from the list givenbelow[List: magnetised, natural, broken, powerful, magnet, surestmagnetic, electromagnets, telegraph.]1. Artificial magnets are preferred to _______ magnets because

they are more _______ .2. A substance which is strongly attracted by a _______ is called

_______ substance.3. _______ are used in telephones and _______ .4. Repulsion is the _______ test of magnetism.5. A piece of iron can be _____ by rubbing a bar magnet over it.6. When a magnet is _______ every piece is a complete magnet.

Ans. 1. natural, powerful 2. magnet, magnetic 3. Electromagnets,telegraph 4. surest 5. magnetised 6. broken.

III. Fill in the blanks.1. The Chinese sailors used natural magnets as _______ .2. Magnet is a term derived from _______ .3. Hammering a magnet violently destroys its _______ property.4. Temporary magnets are usually made of _______ .5. Magnets are used in the construction of certain toys to give

_______ like effect.

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6. A freely floating magnet points in the _______ direction.7. In a magnet, _______ have the greatest magnetic force.8. _______ is a sure test of magnetism.9. There is a very large _______ around the earth.

10. Artificial magnets can be made into different _______ .11. Effective length of a bar magnet is always _______ than

geometric length.12. A freely suspended bar magnet always points towards _______

and _______ .13. Similar poles _______ each other.14. Lodestone is a _______ magnet.15. Electromagnet is an _______ magnet.16. The imaginary line joining north and south pole is called

magnetic _______ .Ans. 1. compass 2. magnetite 3. magnetic 4. soft iron 5. magic

6. north-south 7. poles 8. Repulsion 9. magnetic field 10. shapesand sizes 11. less 12. north and south 13. repel 14. natural15. artificial 16. lines.

IV. State whether the following statements are true or false (T/F).1. If a substance is attracted by a magnet, then the substance is

also a magnet.2. Natural magnets are not used because they have weak magnetic

force.3. Magnetic force can easily pass through non-magnetic sub-

stances.4. A mixture of iron and brass powder can be separated with

magnet.5. Electromagnets can be prepared by passing current around any

metal.6. Repulsion is the surest test of magnetism.

Ans. 1. F 2. T 3. T 4. T 5. F 6. T.V. Classify the following into magnetic and non-magnetic

substances:Wood, iron, copper, air, brass spoon, plastic ruler, soap cake, waterpaper, button, cobalt, nickel, aluminium.


Ans. Magnetic substances: Iron, cobalt, nickel.Non-magnetic substances: Wood, copper, air, brass spoon,plastic ruler, soap cake, water, paper, button, aluminium.

VI. Statements given below are incorrect. Write the correctstatements.1. Natural magnets are stronger than artificial magnets.

Ans. Artificial magnets are stronger than natural magnets.2. A mixture of iron and aluminium powder can not be separated

with a magnet.Ans. A mixture of iron and aluminium powder can be separated with

a magnet.3. Attraction is the surest test of magnetism.

Ans. Repulsion is the surest test of magnetism.4. Alnico is used in the coils of transistors.

Ans. Magnadur is used in the coils of transistors.5. For magnetising a magnetic substance, single-touch method is

better than double-touch method.Ans. For magnetising a magnetic substance, double touch method is

better than single-touch method.6. A magnet has no effect even if it is heated to a very high

temperature.Ans. A magnet gets demagnetised if it is heated to a very high

temperature.7. Permanent magnets lose their magnetism after the magnetising

force is removed.Ans. Temporary magnets lose their magnetism after the magnetising

force is removed.8. Magnetic poles always occur in single.

Ans. Magnetic poles always occur in pairs.9. The north pole of a freely suspended bar magnet will always

face towards geographic south.Ans. The north pole of a freely suspended bar magnet will always

face towards geographic north.10. Iron is a non-magnetic substance.

Ans. Iron is a magnetic substance.

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11. Wood is a magnetic substance.Ans. Wood is a non-magnetic substance.

12. Similar poles attract each other.Ans. Similar poles repel each other.

13. An electromagnet is a permanent magnet.Ans. An electromagnet is a temporary magnet.

14. Aluminium is a magnetic substance.Ans. Aluminium is a non-magnetic substance.

15. Steel is a non-magnetic substance.Ans. Steel is a magnetic substance.

16. Unlike poles of magnets repel each other.Ans. Unlike poles of magnets attract each other.

17. Electromagnets are used for removing brass pieces from ascrap of brass and copper.

Ans. Electromagnets are used for removing iron pieces from a scrapof iron and copper.

18. When a soft iron rod is placed in coil carrying current, itchanges to permanent magnet.

Ans. When a soft iron rod is placed in coil carrying current, itchanges to temporary magnet.

VII. Match the followingColumn A Column B

1. Iron, cobalt, nickel (a) Natural magnet2. Wood, air, water (b) Electromagnet3. Used in large computers (c) Non-magnetic substances4. Used in electric bell (d) Magnetic substances5. Lodestone (e) Ceramic magnet6. Soft iron (f) Magnetic needle7. Steel (g) Alnico8. Magnet made from a mixture (h) Ferrite magnet

of iron oxide and barium oxide9. Magnet made from a mixture (i) Magnetic toys

of aluminium, nickel and cobaltAns. 1. (d) 2. (c) 3. (e) 4. (b) 5. (a) 6. (f) 7. (i) 8. (h) 9. (g).


VIII. Find the odd-one out. Give reasons for your choice.1. Plastic, brass, iron, copper, zinc

Ans. Iron. Only iron is magnetic substance but other are non-magnetic substance.

2. Iron, nickel, cobalt, aluminiumAns. Aluminium. Only aluminium is non-magnetic substance but

other are magnetic substance.3. Magnetic induction, magnetic separation, single-touch method,

double-touch method.Ans. Magnetic separation. Except-magnetic separation, other are

methods for magnetising a magnetic substance.4. Horseshoe magnet, U-shaped magnet, bar magnet, lodestone,

cylindrical magnet.Ans. Lodestone. Only lodestone is a natural magnet but other are

artificial magnets.5. Steel, copper, aluminium, brass.

Ans. Steel. Only steel is magnetic substance but other are non-magnetic substance.

IX. Give reasons for the following.1. Artificial magnets are more used than natural magnets.

Ans. As artificial magnets are more powerful and can be made invarious shapes and sizes hence, artificial magnets are more usedthan natural magnets.

2. A freely suspended magnet comes to rest in the north-southdirection.

Ans. It is because the earth itself behaves like a magnet such that thenorth pole of the earth’s magnet is pointing at the geographicsouth and the south pole pointing at the geographic north.

3. It is impossible to obtain a piece of magnet having only onemagnetic pole.

Ans. As the magnetic poles always occur in pairs, north pole andsouth pole hence, it is impossible to obtain a piece of magnethaving only one magnetic pole.

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4. Most of the iron filings cling near the ends of the magnet.Ans. Because the ends of the magnet have greater magnetic strength

than the centre of the magnet. So most of the iron filing clingnear the ends of the magnet.

5. When a magnet is heated strongly, it gets demagnetised.Ans. Because the kinetic energy of the molecules increases when

magnet are heated strongly. Then the straight chains of themolecules get disrupted and the molecules go back to theclosed chain arrangement.

6. Repulsion is the surest test of magnetism.Ans. Attraction can be caused either by opposite poles of magnets

or between one pole of magnet and an unmagnetised bar of ironwhereas repulsion is possible only between the two similarpoles of magnets. Hence repulsion is the surest test ofmagnetism.

X. Define the following:1. Pole of a magnet 2. Effective length of a bar magnet 3. Magneticinduction 4. Magnetic axis 5. Magnetic meridian 6. Magnetic keeper

Ans. 1. Pole of a magnet. The regions near the ends of a bar magnetwhere the attractive power is most pronounced are called thepoles of the magnet.

2. Effective length of a bar magnet. It is the distance betweenthe magnetic north pole and magnetic south pole.

3. Magnetic induction. The phenomenon due to whichtemporary magnetism is produced in a magnetic substance dueto the presence of a magnet is called magnetic induction.

4. Magnetic axis. The imaginary line passing through themagnetic north (N) and south (S) poles of a bar magnet iscalled magnetic axis.

5. Magnetic meridian. It is an imaginary vertical line passingthrough the magnetic axis of a freely suspended magnet.

6. Magnetic keeper. It is a piece of soft iron. Two such soft ironbars are placed at the either end of the pair of bar magnets. Itis used to avoid self-demgnetisation of magnets.


XI. Differentiate between the following.1. Ferrite magnets and alloy magnets.

Ans. Ferrite magnets Alloy Magnets(1) They are made from a (1) They are made of mixture

powder of iron oxide and of aluminium, nickel, cobaltbarium oxide copper and iron.

(2) They are brittle and have (2) They are very strong andthe properties of ceramics. do not lose magnetism with

normal treatment.(3) It is known under the trade (3) It is known under the trade

name magnadur. names alnico and alcomax.2. Iron and wood.

Ans. Iron is a magnetic material but wood is a non-magnetic material.3. Magnetic induction and single-touch method.

Ans. Magnetic induction is the phenomenon by which an ordinarypiece of iron acquires magnetic properties temporarily due tothe presence of another magnet near it. In single touch method,the magnetic substance is magnetised by rubbing with a magnet.

4. Soft iron magnet and alnico magnet.Ans. Soft iron magnet are temporary magnets which can retain their

magnetism only for a short duration. They lose their magnetismafter the magnetising force is removed.Alnico magnets are permanent magnets i.e. they are able to keeptheir magnetism for a long time even when the magnetising forceis removed.

5. Length of a magnet and effective length of a magnet.Ans. Length of a magnet is the distance between the centre of the

magnet and one of the magnetic poles.Effective length of a magnet is the distance between themagnetic north pole and magnetic south pole.

6. Natural and artificial magnet.Ans. Natural magnets are naturally occurring substances like

lodestone which possesses the property of attracting magneticsubstances.

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Artificial magnets are magnets made by humans using artificialmethods.

7. Permanent and temporary magnet.Ans. Permanent magnets are the magnets which are able to keep their

magnetism for a long time even when the magnetising force isremoved.Temporary magnets are magnets which lose their magnetismafter the magnetising force is removed.

8. Steel and plastic.Ans. Steel is a magnetic material but plastic is a non-magnetic material.

9. Single touch method and double touch method.Ans. Single touch method is a method of magnetising a magnetic

substance by rubbing with a magnet.Double touch method is a method of magnetising a magneticsubstance by rubbing with a pair of magnets.

XII. Answer these questions:1. (a) What is a natural magnet?

(b) How is artificial magnet prepared from a natural magnet?Ans. (a) A material which occurs naturally and has magnetic

properties is called natural magnet.(b) Artificial magnets are prepared by imparting the properties

of natural magnet to the magnetic substances by rubbingwith magnet or by process of induction.

2. (a) What are artificial magnets?(b) Draw diagrams of four artificial magnets.

Ans. (a) Artificial magnets are the magnets made of iron, steel,cobalt or nickel.

(b) (i) Bar Magnet

(ii) Cylindrical magnet

(iii) Dumb-bell magnet.


(iv) U-shaped magnet.

3. Why are artificial magnets preferred to natural magnets?Ans. Artificial magnets are preferred to natural magnets because

(i) they can be made very powerful for using in differentdevices.

(ii) they can be made in any desired shape and size.4. What are (a) magnetic substances (b) non-magnetic sub-

stances? Give four examples of each kind.Ans. (a) Magnetic substances are the substances which are strongly

attracted by magnet or can be converted into magnetartificially. For examples, iron, cobalt, nickel and steel.

(b) Non-magnetic substances are the substances which areneither attracted by magnet nor can be converted intoartificial magnets. For examples, stones, glass, wood,aluminium etc.

5. (a) You have a steel nail 10 cm long. How will you magnetiseit, using a bar magnet?

(b) How will you test the poles of magnet?Ans. (a) We can magnetise a steel nail of 10 cm long by rubbing

a permanent bar magnet over it.(b) The poles of magnet can be tested by bringing ends of

magnet near the north pole of freely suspended magneticneedle. If the north pole of freely suspended magneticneedle gets repelled, then that end of the magnet is thenorth pole of the magnet and if it is attracted then the endof the magnet is south pole.

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6. How will you convert an iron nail about 8 cm long into a magnetwith the help of electric current?

Ans. Wind the iron nail with the insulated copper wire over it. Bare theends of copper wire from insulation, then fixed each end on theterminals of dry cell. Then, the iron nail will change into magnet whencurrent flows around it.

7. State six important properties of a magnet.Ans. Six important properties of magnet are:

(a) it attracts magnetic substances.(b) it points north-south direction when suspended freely.(c) repulsion is the surest test of magnetism.(d) poles of magnets are always in pair.(e) similar poles of magnets repel each other.(f) magnetic force can easily pass through non-magnetic

substances.8. A box contains nails of brass and iron. How will you separate them

by using a magnet?Ans. When we bring a magnet near a box containing nails of brass and

iron, the iron nails will cling at the magnet. Then we can separatethem easily.

9. What are magnetic keepers? How Magnetic keepers are used tostore magnets.

Ans. Magnetic keepers are soft iron bars placed at the either end of thepair of magnets. It is used to avoid self-demagnetisation of magnets.The magnets are arranged in pairs, with opposite poles facing eachother. Two soft iron bars are placed at the either end of the pair ofmagnets.

10. How do you show the directive properties of a bar magnet?Ans. A string is tied at the centre of the bar magnet. When, we suspend

it so that it can hangs freely. Then, the magnet will always point inthe north-south direction, when it comes to rest. This show thedirective property of a bar magnet.

11. Classify magnets on the basis of retention of magnetism.Ans. On the basis of retention of magnetism, we can classify magnets into

two categories.(i) temporary magnet, and(ii) permanent magnet.


12. What are the important uses of magnets.Ans. Uses of magnets:

(i) it is used in magnetic compass,(ii) it is used in pencil boxes, soap stands, refrigerator etc.(iii) ceramic magnets are used in large computers,(iv) it is used in bicycle dynamos,(v) it is also used in toys to give a magical effect.

13. How do you prove that earth itself is a magnet?Ans. A freely suspended magnet always points in the north-south

direction. This shows that our earth itself is like a huge barmagnet with its magnetic poles near the geographical poles. Thenorth poles of earth’s magnet is near the geographical southpole and the south pole of the earth’s magnet is near thegeographical north pole.

14. How will you show that the magnet shows attractive property?Ans. To show the attractive property of a magnet, spread iron filings,

over a sheet of paper. Then, roll the magnet on the filings sothat all parts touch the filings. Iron filings will cling to themagnet when magnet is picked up.

15. Define magnetic induction. How is an unmagnetised piece ofiron magnetised by this phenomenon?

Ans. The phenomenon by which an ordinary piece of iron (or anymagnetic substance) acquires magnetic properties temporarilydue to the presence of another magnet near it is called magneticinduction.An unmagnetised piece of iron can be magnetised by bringinga magnet near the piece of iron.

16. What happens when a magnet is rubbed on a needle with amagnet in only one direction (from one end of the needle to theother)?

Ans. When a magnet is rubbed on a needle with a magnet in onlyone direction, then the needle will magnetised temporarily.

17. Explain the ways by which the magnetic properties of a magnetget destroyed.

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Ans. The magnetic properties of a magnet get destroyed(i) by rough handling.(ii) by hammering it violently several times.(iii) by dropping it on the floor many times,(iv) by heating it to a very high temperature.

18. Explain how a pair of bar magnets can be stored. Draw alabelled diagram showing the arrangement of the magnets andthe keepers.

Ans. A pair of bar magnet canbe stored by arrangingsuch that their oppositepoles lie close together anda keeper is placed on thetwo different polesbelonging to two different magnets which attract it.

19. A horseshoe magnet is to be stored. Draw a labelled diagramshowing the arrangement of the magnet and keepers.

Ans.

This shows the arrangement of horseshoe magnet and thekeeper.

20. Describe an experiment to show that like poles repel each other.Ans. Experiment to show that like poles repel each other:

Suspend a magnet freely from a wooden stand with a thread.When it comes to rest in north-south direction, bring the northpole of another magnet near the north pole of the suspendedmagnet. Then the north pole of freely suspended magnet willrepelled. Repeat the same process with south poles, then alsosouth pole will repel. This shows that like poles repel eachother.


21. Describe an experiment to detect whether a given iron piece isa magnet or not.

Ans. To check whether a given iron piece is a magnet or not.First keep the given iron piece on a wooden table. Then bringone pole say N-pole of a magnet close to the ends of the ironpiece one by one. If one end is attracted and other repelled thenthe iron piece is a magnet. If both ends are attracted then theiron piece is not a magnet.

22. Describe an experiment to show that magnetic poles alwaysoccur in pairs.

Ans. If a bar magnet is broken into two pieces each piece, whenfreely suspended will point in the north-south direction. Thisshows that if a bar magnet is broken into two or more smallerpieces, then even the smallest piece is a complete magnet withtwo poles. This shows that magnetic poles always occur in pairs.

23. Explain the molecular theory of magnetism.Ans. Molecular theory of magnetism states that,

(i) each molecule of a magnetic substance is an independentmagnet.

(ii) in an unmagnetised substance, the molecular magnets arerandomly oriented forming a closed chain.

(iii) in a magnetised substance the molecular magnets arearranged such that the north pole of each molecular magnetpoints in one direction and the south pole in the oppositedirection and the bar has no magnetic property in its centre.

(iv) when a piece of iron is magnetised the molecular magnetsstart setting themselves along straight chains.

(v) when a magnet is strongly heated or hammered the magnetgets demagnetised. It is because the kinetic energy of themolecules increases and straight chains get disrupted.

24. On the basis of the molecular theory of magnetism, explain thefollowing.(a) Magnetisation of iron(b) Demagnetisation of a magnetic material

Ans. (a) When a piece of iron is magnetised the molecular magnetsstart setting themselves along straight chain. As a result themagnetism of the piece increases.

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(n) When a magnet is strongly heated or hammered the kineticenergy of the molecules increases and therefore straightchains get disrupted. As a result the molecules go back tothe closed chain arrangement. Thus, the magnet getsdemagnetised.

25. Every iron atom is a tiny magnet, why all iron bars are notmagnets?

Ans. In an iron bar, iron atoms are randomly oriented. They form aclosed chain so that they neutralise the effect of each other.So, all iron bars are not magnet even though every iron atom isa tiny magnet.

26. What are the characteristic features of the magnetic lines of force?Ans. Characteristic features of the magnetic lines of force are,

(i) each line is a closed and continuous curve,(ii) normally they originate at the N-pole and terminate at the

S-pole of a magnet,(iii) the lines are crowded near the poles where the magnetic

field is strong and are far apart where the field is weak.(iv) they do not intersect each other.

27. Describe an experiment to prove that maximum magnetic forceacts at the poles of a magnet.

Ans. Take a bar magnet and place a steel pin at some distance.Nothing happens. Then, bring the steel pin near the pole of thebar magnet. It will stick to the magnet. This experiment showsthat maximum magnetic force acts at the poles of a magnet.

28. With the help of a labelled diagram show the difference betweenthe magnetic lines of force in a bar magnet and a horseshoe magnet.

Ans.(a) Magnetic lines of force in a bar magnet.


(b) Magnetic lines of force in a (U-shaped magnet) horseshoemagnet.

29. With the help of a labelled diagram show the magnetic lines offorce formed when the unlike poles of two bar magnets faceeach other.

Ans. Magnetic lines of force when the unlike poles of two barmagnets face each other.

XIII. Numerical Problems:1. A long magnet is broken into 10 pieces. How many north poles

will be there in(a) 10 pieces? (b) one piece?

Ans. (a) 10 north poles in 10 pieces.(b) 1 north pole for 1 piece.

2. If the length of a magnet is 2 cm, what is its effective length?Ans. Length of magnet = Length of one of the magnetic pole from

the centre= 2 cm

... Effective length = Distance between two poles= 2 cm + 2 cm = 4 cm.

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6 magnetism - the assam valley school today/worksheets/6/magneti… · class-vi physics question...

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