VI CLASS (NON IAS) - PHYSICS

Class - VI PHYSCIS (NON IAS)

Chapter – 1
Introduction to Physics

1. What is Science? What are its two main classes?
A. Science is a systematic study of things. The two main classes of science are Physical Science and Natural Science.

2. State one difference between: Physical Science and Natural Science.
A. Physical Science is the study of non-living things and Natural science is the study of living things.

3. What is Physics?
A. Physics is the study of phenomena which are taking place in matter and energy.

4. What do you understand by the term phenomenon?
A. Any event which happens around us is a phenomenon.

5. When does a hypothesis become a theory?
A. A hypothesis when supported by carefully designed experiments becomes a theory.

6. Name the five senses which we employ to study a phenomenon.
A. The five senses are:
i) Sense of sight
ii) Sense of smell
iii) Sense of taste
iv) Sense of touch and
v) Sense of hearing.

7. Name any three modern modes of transportation. Which one is fastest among them?
A. Ships, Aeroplanes and trains are the three modern modes of transportation. Aeroplane is the fastest mode of transportation.

8. Name three problems which are yet to be solved by Physics.
A. i) Physics has yet to control the forces which produce earthquakes, floods, tornadoes, typhoons and other natural calamities.
ii) The problems of disposal of nuclear wastes produced in atomic power plants.
iii) Alternative sources of energy to the fossil fuels.
9. Differentiate between the following:
a) Botany and Zoology
b) Chemistry and Physics.
a) Botany is the study of plants and Zoology is the study of
animals.
b) Chemistry is the study of composition of matter and physics is
the study of matter and energy.

Chapter – 2
Fundamental Measurements

1. Name four early units of measurement of length.
A. Out stretched palm, foot, arm, yard.

2. Why do we need standard units for measurement?
A. We need standard units for measurement as the earlier units are different for different people

3. What are Standard International units of measurements? State the unit of length, mass and time in this system.
A. Set of units of Measurement of mass, length, time, temperature is called standard international system of units. Unit of length is metre, mass is kilogram, time is second in this system.

4. Define the term metre. Name two sub-multiples and one multiple of metre.
Fig.2.20 shows a pencil, whose length is measured by placing eye at A, B and C. In which position of eye is the accurate measurement of length recorded? What is the magnitude of accurate length? What is the magnitude of length eye is placed in other position?
Refer figure 2.20 page no. 25

A. Metre is the length between two fine marks on a metal bar made of platinum – iridium alloy maintained at constant temperature and is placed on two rollers.
Centimetre and millimetre are the sub-multiples of metre. Kilometre is the multiple of metre.
In position B, we get accurate measurement. 8 is the magnitude 8.1 is the magnitude of length in position A and 7.9 in position C.


5. By using a thin cotton thread, how will you find the length of a curved line?
A. Fix common pins on the sharp ends of curved line. A, B………F, etc., are the pins fixed on the curved line. Now tie a knot with cotton thread at the common pin A. Using fingers of both hands move the thread along the curved line such that it goes around pins B, C …………………F, etc.

Care should be taken that thread is neither too tight nor too loose, when moved along the curved line. When the thread reached the extreme end of the curved line, cut it from that point.

Remove the thread from A and then place it straight along the length of half metre scale. The length of the thread is equal to the length of curved line.

6. What do you understand by the term mass?
A. Mass is the amount of matter contained in a substance.

7. Name the SI unit of mass. State two multiples and two sub-multiples of mass.
A. Kg is the S.I. unit of mass. Quintal and metric tonne are the multiples, gram and milligram are the sub multiples of mass.

8. a) How many decades make one millennium?
b) How many centuries make one millennium?
c) How many years make one millennium?
A. a) 100 b) 10 c) 1000

9. What is meant by the term mean solar day? How many hours are there in one mean solar day?
A. The average of all solar days in which earth completes one revolution around the sun is called mean solar day. There are 24 hrs in a mean solar day.

10. State the fundamental unit of time. State the fractional value of this unit in terms of mean solar day.
A. Second is the fundamental unit of time
1 Second = part of mean solar day.

11. a) What is a 24 hours clock? B) Which two organizations use 24 hour clock ?
A. a) It is a convention of time in which the day runs from midnight to midnight and is divided into 24 hours, numbered from 0 to 23.
b) Railway Stations and air ports.

12. The time on the 24 hour clock is a) 08 h – 37 min b) 23 h – 48 min. Express the time on 12 hour clock.
[ (a) 08 h – 37 min AM (b) 11 h – 48 min PM]
A. a) 08 h – 37 min
08 h – 37 min A.M
b) 23 h – 48 min

23 h – 48 min
12 h – 00 min
____________________
11 h – 48 min P.M.
____________________

13. A brass bob is suspended by a thin strong thread and allowed to oscillate, such that length of the pendulum is 1 m.
a) In how many seconds will this pendulum complete one oscillation?
b) If a boy finished a race, when this pendulum makes a race, when this pendulum makes 11 oscillations, how much time does the boy take in finishing the race?
A. a) 2 s
b) Time taken for 1 oscillation = 2 s
Time taken for 11 oscillation = 11 x 2 = 22 s

14. a) What do you understand by the term temperature?
b) Name a device used for measuring temperature.
c) Name the scale in which temperature is measured.
d) What is the temperature of i) pure boiling water ii) pure melting ice?

A. a) Temperature is the degree of hotness or coldness of a body.
b) Thermometer
c) Celsius
d) i) 1000C ii) 00C

15. a) State SI unit of temperature
b) What is the magnitude of temperature in SI scale for:
i) Lower standard point?
ii) Upper standard point?
A. a) Kelvin
b) i) 273
ii) 373

16. a) What is a clinical thermometer?
b) Why is this thermometer marked between 350C and 430 C?
c) What is the normal temperature of the human body?
d) What conclusions can be drawn if the temperature of a patient is
i) 39.40C ii) 35.20C ?
A. a) The thermometer used to measure the temperature of a human body is called clinical thermometer.
b) It is because the temperature of a human body does not fall below 350C nor does it rise above 430C, as in either case death occurs.
c) 370C
d) i) 39.40C
The patient is having a high temperature and running down with fever.
ii) 35.20 C
The patient is weak and the body is not generating enough heat energy.

17. a) What do you understand by the term estimation?
b) Is estimation a reliable way of measurement? Support your answer with an example.

A. a) Estimation is a quick judgment about a measurement of some particular quantities.
b) Estimation is not a very reliable way of measurement.
Example: A chemist while dispensing drugs has to weigh them very accurately as a few milligrams of excess drug can cause serious problem for the patient.

18. Figure 2.21, page no. 25 of the text book shows four identical wooden rods, placed side by side, such that their total thickness is 5 cm. Find the thickness of a single rod, correct to two decimal places.

A. Thickness of 4 wooden rods = 5 cm
Thickness of a single rod = cm = 1. 25 cm

19. 24 coins are placed one upon another and their total thickness is recorded by a half metre scale. The thickness is found to be 4.8cm. Find the thickness of each coin in millimeters.
A. Thickness of 24 coins = 4.8 cm
Thickness of each coin = cm = 0.2 cm = 2 mm

CHAPTER – 3
Measurement of Area and Volume

1) a) What do you understand by the area of an object?
Ans: The amount of surface of a place occupied by an object is called its
area.
b) State the standard international unit of area.
Ans: In standard international system, the unit of area is square metre.
c) How can we find the area of a rectangular body if we know its length and
breadth?
Ans: The area of a rectangular body can be found by finding the product of its length
and breadth.

2) A school hall measures 20m in length and 12m in breadth. Find its area.
Ans: Length of the hall = 20m
Breadth of the hall = 12m
Area = length x breadth
= 20m x 12m
= 240m2

3) Name two sub – multiples and two multiples of standard international unit of area.
Ans: The two sub – multiples of standard international unit of area are 1 cm2 and
1 mm2. The two multiples are hectare and 1 Km2.

4) Name the units in which you will measure the area of the following objects:
i) A 25 paise coin (ii) A playing card (iii) Area of your class room
(iv) Area of a big agricultural field (v) Area of a district.
Ans: i) cm2 (ii) cm2 (iii) m2 (iv) hectare (v) km2

5) The length of a school compound is 450m and breadth is 145m. Find the area of compound in (i) m2 (ii) hectares.
Ans: Length of a school compound = 450m.
Breadth of a school compound = 145m.
(i) Area of the compound in m2 = length x breadth
= 450m x 145m
= 65250m2
(ii) Area in hectares = hectares = 6.525 hectares.

6) A district has a length of 20 km and breadth 17 km. Find the area of district
(i) km2 (ii) hectares
Ans: Length of the district = 20km
Breadth of the district = 17km
(i) Area in km2 = length x breadth
= 20km x 17km
= 340km2
(ii) Area in hectares = 340 x 100 hectares
= 34000 hectares.

7) (a) What do you understand by the term volume of a substance?
Ans: The space occupied by a substance (solid, liquid or gas) is called volume.
(b) State the unit of the volume in standard international system.
Ans: Cubic metre or m3
(c) Define the unit of volume in standard international system.
Ans: One cubic metre is the volume occupied by a cube whose each side is equal to1m.

8) a) Why the volume of a matchbox is not measured in standard international
System?
Ans: The volume of a matchbox is not measured in standard international system as
cubic metre is a fairly inconvenient unit for measuring such small volume.
b) Name and define the unit in which the volume of matchbox is measured.
Ans: One cubic centimeter is the volume occupied by a cube whose each side is
equal to 1cm.
c) Describe in detail how will you find the volume of matchbox using a
centimeter ruler.
Ans: Using a centimeter ruler, first find the length, breadth and height of the
Matchbox in centimeter. The product of length, breadth and height gives the
volume of the matchbox in cubic centimeter.

9) By using overflow jar, how will you measure volume of a glass stopper?
Ans: An overflow jar consists of an iron vessel which is provided with a spout. Fill the
overflow jar with water till the water is at the point of over – flowing.
Under the spout of overflow jar, place a measuring cylinder. Gently lower
the glass stopper in the overflow jar. The glass stopper displaces water which
flows out from the spout into the measuring cylinder. Record the volume of water
overflown. This gives us the volume of the glass stopper.

10) Amongst the units of volume (i) cm3 (ii) m3 (iii) litre
(iv) milliliter, which is the most suitable for measuring :
a) Volume of a swimming tank b) Volume of a glass filled with milk
c) Volume of an exercise book d) Volume of air in a room.
Ans: a) m3 b) milliliter c) cm3 d) litre

11) Find the volume of a book of length 25cm, breadth 18cm and height 2cm.
Ans: Length of the book = 25cm
Breadth of the book = 18cm
Height of the book = 2cm
Volume of the book = length x breadth x height
= 25cm x 18cm x 2cm
= 900cm3

12) The level of the water in a measuring cylinder is 12.5ml. When a stone is lowered
in it, the volume is 21ml. Find the volume of the stone now.
Ans: Level of water in the measuring cylinder = 12.5ml
Volume of water after the stone is lowered = 21ml
Volume of stone = 21ml – 12.5ml
= 8.5ml

CHAPTER – 4
Some Facts About Force

1) a) Name two effects a force can have on a moving body.
b) What do you understand by the term force?
c) Name two effects a force can have on a stationary body.
Ans: a) 1)A force can make a moving object move faster.
2) Force can change direction of moving objects.

b) Force is an external agent which changes or tends to change the state of rest or uniform
motion of a body or changes its direction or shape.

c) 1) A force can cause a motion in stationary object.
2) Force can change the shape of an object.

2) Name the type of force which acts in each of the following cases:
a) A cricket ball rolling down a cricket field.
b) A stone thrown vertically upward.
c) A bullock ploughing a field.
d) A woodcutter cutting a tree.
e) A plastic ruler on being moved through dry hair, is brought near dry pieces of straw.
f) Fast moving wind driving a windmill.
g) Falling of rain drops.
h) Attraction of common pins towards magnet.
i) Closing of door.
j) A horse pulling a cart.
Ans: a) Consequential force
b) Gravitational force
c) Muscular force
d) Muscular force
e) Electrical force
f) Mechanical force
g) Gravitational force
h) Magnetic force
i) Muscular force
j) Muscular force.

3) What do you understand by the (a) Contact forces, (b) Forces at a distance, (c)
Consequential forces? Support your answer with examples.
Ans: (a) Contact forces : All forces which act on a body directly or through a connector, are called contact forces. Example : we can pull a cart by attaching a rope or rigid handle of metal or wood.
(b) Forces at distance: The forces which do not make direct contact with a body, but act through space, are called forces at distance. The force of gravitation, the magnetic force and electrical force, are the examples of forces at distance.
(c) The consequential force can be defined as a force which is called into play, when a force is applied on an object.
Example: when a cricket ball is made to roll on the ground by applying force, it stops after covering a certain distance, although, no force is applied to stop it. This force of friction is consequential force.

4) a) State the unit of force and define it.
b) Name the unit of force in standard international (SI) system. How much mass
can be lifted by this force in grams?
Ans: a) The unit of force is kilogram force. It is the force required to lift a mass of
1kg in the vertically upward direction.
b) The unit of force in SI system is Newton. 100g of mass can be lifted by a force
of 1 N.

5) a) What do you understand by the term force of friction?
b) Give two examples, where force of friction is a hindrance.
c) State two ways of minimizing friction.
Ans: a) A force which acts at the surface of contact, when one body moves upon another body, is called force of friction.
b) i) Friction wears out the soles of shoes. It wears out the types of all kinds of vehicles. Thus the soles of shoes or tyres need replacement from time to time.
ii) Friction wears out the moving parts of machinery. It also heats up the moving parts and they need replacement from time to time.
c) 1) By oiling or greasing the moving parts of machinery the friction can be considerably reduced.
2) Friction can be reduced by providing wheels.

6) a) When does force of friction come into play?
b) If a force is applied toward East, in order to move a body, in which direction does the force of friction act?
Ans: a) A force of friction comes into play when an object moves in contact with another object.
b) West.

7) Why are tyres provided with deep grooves on their surfaces?
Ans: Tyres of all kinds of vehicles are provided with deep grooves, so as to increase friction. This prevents the vehicle from skidding on wet roads and sharp turns.

8) Why does a knot tied with jute thread not slip easily, as compared to silk thread?
Ans: Knot with silk thread slips easily, compared to that of the jute thread, because jute offers more friction than silk.

9) What would happen if there is no force of friction?
Ans: If there is no friction, the bodies will either slip or will not move.

CHAPTER – 5
Pressure

1) (a) Define the term pressure.
Ans : The thrust (compressive force) acting per unit area is called pressure.

(b) State and define the SI unit of pressure.
Ans : In SI system, the pressure is measured in Pascal.

2) Explain the following:
a) Why are double tyres provided at the rear wheels of a truck?
Ans : Rear wheels of buses or trucks are provided with double wheels to prevent tyres
from sinking in ground or to prevent damage to the roads.

b) Why does a camel easily cross the desert but not a horse?
Ans : A camel can easily cross the desert as compared to a horse because the camel
exerts very small pressure on the ground as it has very broad feet.

c) Why are long skis used for gliding over snow?
Ans : The skiers use flat and long skies to slide on the snow because the larger the area of
cross – section, the less is the pressure on the snow. Hence, a skier can easily slide
over snow without sinking his feet in the ground.

d) Why is the foundation of a building made very wide, as compared to its walls?
Ans : Foundation of high rise buildings are kept very wide so that they do not sink under
the extremely high pressure of buildings.

e) Why do the army tanks move over the wide steel chain rather than on the wheels?
Ans : Army tank is made to move over broad steel tracks rather than on wheels, as the
broad tracks increase the area of cross – section and reduce pressure on the ground.

f) Why is the edge of knife kept sharp?
Ans : Knives are sharpened from cutting edge as the area of cross – section decreases,
and hence, pressure exerted by them increases. Thus, they can easily penetrate a
given surface.

g) Why is one end of drawing board pin broad and flat, whereas its other end is
pointed and sharp?
Ans : Drawing pin is kept broad from the thumb side but very sharp from the pin side.
The broader thumb tack reduces pressure on thumb but sharp pin tip increases
pressure on wooden board, and hence, it can easily penetrate it.

h) Why does a sharp nail easily penetrate wood, but not a blunt nail?
Ans : The area of cross – section of a sharp nail is less than the blunt nail. So, more
pressure is applied and it can easily penetrate wood.

3. A force of 16 N acts on an area of 50 Cm2. What is the magnitude of pressure in pascal?
Sol: Force (F) = 16 N
Area (A) = 50 Cm2
= 50 / 10000 m2 ( 1 cm2 = 1 / 10000 m2 )
= 1 / 200 m2
Pressure (P) = F / A
= 16 x 200 N / m2
= 3200 Pa

A force of 200N acts on an area of 0.16 m2. What is the magnitude of pressure in pascal?
Sol: Force(F) = 200N
Area(A) = 0.16m2
=16/100 m2
Pressure (P) = F/A
= 200x100/16 N/m2
= 1250 N/m2
= 1250 Pa

5. What is the magnitude of force which produces a pressure of 7000 Pa. While action on a surface of a area of cross – section 0.25 m2?
Sol: Force (F) = ?
Area (A) = 0.25m2
= 25 / 100 m2
Pressure (P) = 7000 Pa
P = F / A
F = P x A
= 7000 x 25 / 100
= 1750 N.

6. A force (F) acts on an area of 600 cm2 and produces a pressure of 12500 Pa. Calculate the magnitude of F?
Sol: Force (F) = ?
Area (A) = 600cm2
= 600 / 10000m2
= 3 / 50m2
Pressure (P) = 12500 Pa
P = F / A
F = P x A
= 12500 x 3 / 50
= 750 N

7. A force of 300 N, while action on an area A, produces a pressure of 1500 Pa. Calculate the magnitude of A in cm2?
Sol: Force (F) = 300 N
Pressure (P) = 1500 Pa
Area (A) = ?
P = F / A
A = F / P
= m2
= m2
= x 10000 cm2
= 2000 cm2

8. What is the area cross – section of a body in m2, when it exerts a force of 50 N and produces a pressure of 2000 Pa?
Sol: Force (F) = 50N
Pressure (P) = 2000 Pa
Area (A) = ?
P = F / A
= m2
= m2
= 0.025 m2.


CHAPTER - 6
Energy and Work

1) a) What do you understand by the term energy?
Ans : Ability to do work is called energy.

b) Name two basic kinds of energy.
Ans : Energy has been divided into two kinds, i.e., kinetic energy and potential energy.

2) a) What do you understand by the term work?
Ans : When a force causes displacement in its own direction, work is said to be done.

b) State two factors which determine the work done by a body.
Ans : The two factors which determine the work done by a body are :
(i) There must be a force acting on the body.
(ii) The body must move in the direction of applied force.

c) State a situation in which force is applied on a body, but no work is done.
Ans : A boy standing with his school bag on his back.

d) Write the mathematical expression for work.
Ans : W = F x S

3) a) What do you understand by the term kinetic energy?
Ans : The energy possessed by a body due to its motion is called kinetic energy.

b) Give four examples of kinetic energy.
Ans : (i) A running train (ii) A speeding car (iii) A shooting arrow and (iv) A stone
rolling down a hill.

c) State two factors which determine kinetic energy.
Ans : The two factors are :
(i) The more the mass of a body, the more is its kinetic energy.
(ii) The more the speed of a moving body, the more is its kinetic energy.

d) Two bodies have equal mass. However, speed of one body is double than that of
the other. Which of the two bodies has more kinetic energy?
Ans : The body moving with more speed has more kinetic energy.

4) a) What do you understand by the term potential energy?
Ans : The energy possessed by a body due to its position or configuration is called
potential energy.

b) State two factors which determine potential energy.
Ans : The two factors which determine potential energy are weight of a body and the
distance through which a body is raised.

c) Give four examples of potential energy.
Ans : (i) Wound – up spring of an alarm – clock. (ii) Water stored in a tank (iii) Stretched bow and arrow and (iv) Stretched rubber of a catapult.


5) State the kind of energy (potential energy or kinetic energy) possessed by the
Following.
Ans : (a) A stone resting at the top of hill. Potential energy.
(b) An arrow shooting from a bow. Kinetic energy.
(c) A flying mosquito. Kinetic energy.
(d) A wound up spring of a toy car. Potential energy.
(e) A speeding car. Kinetic energy.
(f) A bullet fired from a gun. Kinetic energy.


CHAPTER - 7
Simple Machines

1) a) What do you understand by the term machine?
Ans : A machine is a device which helps us to lift heavy loads, or speed up the motion or
change the direction of force in a desired direction.

b) Name six simple machines.
Ans : (i) Lever (ii) pulley (iii) Inclined plane (iv) Wedge (v) Screw and
(vi) Wheel and axle

2) State four objectives which can be achieved by a machine.
Ans : The four objectives which can be achieved by a machine are
(i) To lift a heavy load by applying a small effort, i.e., to multiply effort.
(ii)To speed up the motion of a body.
(iii)To change the effort in the desired direction.
(iv)For doing unsafe and dangerous work.

3) a) Define lever.
Ans : A lever is a rigid bar which can rotate about a fixed point or a fixed line, called the
axis of rotation. The point or the axis of rotation is called the fulcrum.

4) Give two examples each for the levers of first, second and third order.
Ans : (i) Levers of first order : See – saw, Scissors.
(ii) Levers of second order : Wheel barrow, nut – cracker.
(iii) Levers of third order : A bread knife, fire tongs.

5) Classify the following as levers of first, second and third order :
(i) Forceps : Lever of third order.
(ii) Lock and key : Lever of second order.
(iii) Pliers : Lever of first order.
(iv) Fishing rod : Lever of third order.
(v) A nut cracker : Lever of second order.
(vi) A see – saw : Lever of first order.

6) a) What for single pulley is commonly used?
Ans : Single pulley is commonly used in drawing water from village wells.

b) State one use of single movable pulley.
Ans : Crane is an application of single movable pulley.

7) a) What is an inclined plane?
Ans : Any sloping flat surface along which a load can be easily pushed or pulled is called
an inclined plane.

b) Give four examples of inclined plane, commonly used in daily life.
Ans : Wooden plank, ramp, gang plank,chute.

8) a) What is a wedge? Give three examples of wedge.
Ans : A double inclined plane is called a wedge. Examples : chisel, axe, knife.

b) What for a wedge is employed commonly?
Ans : A wedge is used to tear apart solid object.

9) What is wheel and axle? Give two examples of wheel and axle?
Ans : Wheel and axle essentially consists of two cylinders of different diameters joined
together, such that if one is made to rotate the other also rotates.
Examples : door knob, a screw driver

10) a) What is a screw?
Ans : A rotating inclined plane is called a screw.

b) Give three uses of screw.
Ans : (i) They are used to fasten two pieces of wood or metal.
(ii) A cork screw is used for pulling out cork from the bottles of ketchup or wine.
(iii) Screw jack is basically a nut and bolt arrangement used for lifting one side of
a car or a truck, in order to change the punctured wheel.

11) Classify the following simple machines:
Ans : (i) A railway signal : lever.
(ii) A door knob: Wheel and axle.
(iii) A screw jack : Screw
(iv) A staircase : inclined plane.
(v) An axe : Wedge
(vi) A wheel barrow : lever



CHAPTER – 8
Some Facts About Magnet

1. a) What is a natural magnet?
Ans: A material which occurs naturally and has magnetic properties is called natural
magnet.

b) How is artificial magnet prepared from a natural magnet?
Ans: Artificial magnets are made by rubbing natural magnets on iron and steel.

2. What are artificial magnets?
Ans: A substance to which properties of natural magnet are imparted by artificial
means is called an artificial magnet.

3. Why are artificial magnets preferred to natural magnets?
Ans: Artificial magnets can be made very powerful which is not possible in case of
natural magnets. They can be made in any desired shape or size.

4. What are (a) magnetic substances (b) non - magnetic substances? Give four
examples of each kind.
Ans: a) The substances which are strongly attracted by magnet or can be converted into
magnet artificially are called magnetic substances.
Ex: iron, cobalt, nickel and steel.

b) The substances which are neither attracted by magnet nor can be converted into
artificial magnets are called non – magnetic substances.
Ex: stone, glass, wood and paper.

5. a) You have a steel nail 10cm long. How will you magnetise it using bar magnet?
Ans: Take a steel nail about 10cm long. Place it along one edge of wooden table. At one end, place north pole of the bar magnet. Rub the magnet along the length of the nail. Now lift the magnet and place it at the starting end. Repeat the rubbing process 40 times.
Now bring the end A of the steel nail near the north pole of freely pivoted magnetic needle. Then the north pole of freely suspended magnetic needle is repelled. So, the end A of the steel nail changed into north pole of magnet. Similarly, if we bring end B of the steel nail near the south pole of freely pivoted magnetic needle, then again repulsion takes place. Thus the steel nail gets magnetized.

b) How will you test the poles of magnet?
Ans: Take a magnetic needle and suspend it by a fine thread such that it points in north - south direction. Now bring the pole of a bar magnet near the north pole of the freely suspended magnetic needle. If the pole of bar magnet is repelled, then the pole brought near is also north pole because like poles repel each other. If the pole of magnet attracts the needle, it means that it is south pole. This is because unlike poles attract each other. From this we can test the poles of a magnet.


6. How will you convert an iron nail about 8 cm long into a magnet with the help of electric current?
Ans. Take an iron nail about 8 cm long and wind over it an insulated copper wire. Bare the ends of copper wire from insulation. Fix each end of bare copper wire on the terminals of a dry cell. Hold the copper wire at terminals with cello tape.

Bring the above arrangement near the iron paper clips placed on the table. It is observed that iron paper clips cling to the wire. This proves that the iron nail changes to magnet when current flows around it.

Now remove the wire from the dry cell. It is found that paper clips fall down. From this we conclude that the iron nail behaves like magnet only as long as current flows around it.

7. State six important properties of a magnet.
Ans. Properties:
i) A magnet attracts magnetic substances (iron, steel, cobalt, nickel) towards
itself.
ii) When suspended freely, it points in north- south direction.
iii) Similar poles of magnet repel each other.
iv) Opposite poles of magnet attract each other.
v) Repulsion is the surest test of magnetism.
vi) When a magnet is broken, then each piece is a complete magnet.

8. What are magnetic keepers? How magnetic keepers are used to store magnets.
Ans. Two soft iron bars placed at the either end of the pair of magnets are called magnetic keepers. This system forms a giant magnetic chain, and hence protects them from demagnetisation.

9. A box contains nails of brass and iron. How will you separate them by using a magnet?
Ans. Place an electro magnet in the box containing nails of brass and iron then the iron nails are removed from the scrap as they are attracted towards the electro magnet.


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