TH—Revised Edition Physics For ICSE—6
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TH—Revised Edition Physics For ICSE—6
ANSWER KEY
Chapter 2: Measurement
Exercises (Pages 28, 29 and 30) Q. 1 (a) A unit which is agreed upon and acceptable by a majority of people
to use as a basic unit of measurement is called standard unit.
(b) SI unit of length—metre (m)
It is the distance between two end marks on a rod made up of an
alloy of platinum and iridium at 0°C.
Span, palm, cubit, uncia etc. are some units of length used in the
earlier times.
(c) Sub multiple units of length—mm, cm, dm (two examples)
Multiple units of length—km, dm, hm, (two examples)
Multiple units are used for measuring large lengths such as distance
between home and school or distance between Delhi and Agra.
Submultiple units are used to measure small length such as that
of pencil, or a comb, or a book.
(d) We wrap a thread around a pencil leaving no gaps. We make 25
to 40 turns to form a tight coil. We place this coil against a scale
and measure the length of the coil. The total length divided by
the number of turns of the coil gives the thickness of the coil.
Thickness of the thread =
Length of the coil
Number of turns
(e) (i) L
ower fixed point of laboratory thermometer is 0°C, lower
fixed point of clinical thermometer is 35°C (95°F), upper
fixed point of laboratory thermometer is 100°C, upper fixed
point of clinical thermometer is 42°C (110°F). Human body
temperature does not fall below 37°C (98.6°F) nor does
it rise above 42°C, as in both cases it would cause death.
Normal body temperature is 37°C, a person has fever if the
temperature of his/her body rises above 37°C or 98.6°F.
(ii) Temperature of boiling water is 100°C or more upper fixed
point of clinical thermometer is 43°C. Mercury will rise in the
capillary tube and may burst the thermometer.
(f) SI unit of time—seconds (s)
1
It is
part of a mean solar day.
86400
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Price : `18.00
(g) The kink prevents the mercury from contracting and falling back
into the bulb when the thermometer is taken away from the
patient’s body. So the temperature can be read at leisure.
(h) Same answer as in question (1) (e) (i)
(i) Figure 2.21, Figure 2.20 (pg. 23, textbook)
(j) Figure 2.10 Measuring the area of a leaf (textbook, pg-15)
Method : A flat, lamina-shaped, irregular object, such as leaf, is
taken. It is placed on the graph paper with squares of 1 cm each.
The outline of the leaf is neatly marked with a sharp pencil on the
graph paper. Then we remove the leaf encloses many complete
squares and a few incomplete squares within the leaf’s outline are
counted and noted. Next, the number of incomplete squares are
counted. That is those, which are half on more than half within
the outline. The squares which are less than half can be ignored.
Approximate area
of the leaf
2
Since the area of each square is 1 cm , the area of the leaf, after adding the number of squares, turns out to be that many cm2.
= number of complete squares
+ number of incomplete squares
(k) Method—an appropriate amount of water is taken in a measuring
cylinder and its initial level is noted. The irregular solid whose
volume is to be measured is tied with a string and slowly immersed
in the water. The solid should not touch the bottom or the sides of
the cylinder. On completely immersing the solid, the water level
in the cylinder rises. The new level is noted.
Volume of irregular solid = Final level – Initial level
See Figure 2.15 (textbook, pg-18).
(l) Precautions to be taken to reduce errors in measuring length.
(i) The scale should be placed exactly along the length to be
measured.
(ii) The ruler or scale must not have frayed or worn out edges.
Bevelled or slanting edges are given on rulers and scales for
accuracy.
(iii) To read the scale, the eyes should be placed in line or in front
of or vertically above the measurement to be taken.
(m)(i)Mean solar day—The average of all the solar days in which
the earth make, one complete revolution is considered, which
is known as mean solar day.
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(ii) Mass—Mass is the quantity of matter contained in a body.
(iii) Temperature—Temperature is the degree of hotness or
coldness of a body.
(n) Average of a quantity gives us a fair approximation or estimation
of that quantity.
(o) The shopkeeper weighs 15 kg of rice. Then he divides them into
two equal parts and weigh them by putting the two in both of
balance. If both pans carry equal quantities, then the beam remains
horizontal. Thus 7.5 kg is obtained.
Q. 2 (a)Tonne
(b)Centimetre
(c) Hour
(d)Kilogram
2
(e) Metre square (m )
3
(f) Metre cube (m )
3
Q. 3 Volume—mm
Distance (length)—mm
Mass—mg
Time—days
Temperature – Fahrenheit
3
Q. 4 (a) (i) Volume = 4 × 2 × 3 = 24 cm
(ii) Volume = 8 × 1 × 2 = 16 cm3
(iii) Volume= 1 × 1 × 16 = 16 cm3
Volume in (i) is maximum.
(b) (i) Area = 4 × 3 = 12 cm
(ii) Area = 8 × 1 = 8 cm
2
2
(iii) Area = 1 × 1 = 1 cm2
Area of (i) is maximum.
30
Q. 5 (a) (i)
× 6 = 10°C
18
30
× 12 = 20°C
(ii) 18
(b) Clinical thermometer
(c) No, Because
(i) Water is transparent, reading becomes difficult.
(ii) Boiling point is 100°C and freezing point is 0°C.
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So, we can only measure temperature between this range.
(iii) Water absorbs large amount of heat from the body.
Q. 6 (a) Receive frequency of television transmission.
(b) Used to measure very small lengths such as diameter of a wire.
(c) Used to listen Heart beat
(d) For weather forecast
(e) For knowing time
(f) To see microorganism
30
2
= 1.2 m
Q. 7 (a) Area = 4 ×
100
450
3
(b) Volume = 5 ×
× 4 = 90 m
100
(c) Volume = 3.6 × 3.6 × 3.6 = 46.656 m3
(d) Area = 24 × 21 = 504 km2
(e) Volume = 60 × 25 × 15 = 22500 cm3
22500
Mass = 22500 × 1 = 22500 g = = 22.5 kg
1000
(f) Volume = (33.2 – 24.7) mL = 8.5 mL = 8.5 cm3 [∴1 mL = 1 cm3 = 1 cc]
= 8.5 cc
Q. 8 (a) 6 kg = 6000000 mg = 6000 g
80
= 0.08 km
(b) 80 m = 8000 cm =
1000
2
2
2
(c) 9 km = 9000000 m = 90000000000 cm
12 1
1
(d) 12 hours = =
day =
× 60 × 24 = 720 min
24 2
2
(e) 2 m3 = 2000000 cm3 = 2000000000 mm3
(f) 42 litres = 42000 mL
Q. 9(a) 17 : 30
(b) 06 : 42
(c) 22 : 06
(d) 04 : 32
(e) 23 : 45
(f) 00 : 00
Q. 10 (a) False, 320 K (318 K)
(b) False, same (not same)
(c) False, kilometre (metre)
(d)True
(e)True
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Q. 11 (a)(iii)
(b)(ii)
(c)(i)
(d)(iii)
(e)(iv)
(f)(i)
Chapter 3 : Force and Pressure
Exercises (Pages 45, 46 and 47)
Q. 1 (a) Force is that physical cause which changes or tends to change the
state of rest or motion of an object or the shape of an object.
Effects : (i) A force can cause motion in a body at rest.
(ii)A force can stop a moving body.
(iii) A force can change the speed of a moving body.
(iv) A force can change the direction of a moving body.
(v) A force can change the shape or size of a body.
(b) Speed of motion increases.
(c) Newton (N), Kilogram force (kgf)
(d) 1 kgf is the weight of a body of mass 1 kg. It is the force required
to lift a body of mass 1 kg vertically upwards.
(e) Friction is the force that acts between two bodies in contact when
one body tries to move against the other.
Friction opposes motion, produces heat and causes wear and tear.
(f) Friction opposes motion, causes wear and tear, produces heat,
reduce efficiency of machine but without friction we cannot walk,
we cannot write, we cannot grip, we cannot light matchstick so,
friction though evil is also necessary for modern civilization.
(g) The thrust (force acting normally) acting per unit area is called
F
pressure. P =
A
SI unit of pressure—N/m2 or Pascal (Pa). One pascal is the
pressure acting on a surface when 1 newton force acts normally
on an area of 1 square metre.
(h) Two forces of the same magnitude which act in opposite directions
cancel each other and the resultant force is zero. Such forces are
called balanced force.
For example, planets revolving around Sun, centripetal and
centrifugal forces balance each other.
(i) Weight of a body is the force by which earth attracts a body towards
itself.
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(j) Electrostatic forces—The forces acquired by non-conductors due
to friction.
Magnetic forces—The force exerted by the magnet on magnetic
substances is known as magnetic force.
The similarity between electrostatic and magnetic forces is that
both are non-contact forces.
(k) Camels have broad feet, which reduces the pressure exerted on
the sand, as area of contact is large. This prevents the camel’s feet
from sinking into the sand while walking through the desert.
(l) Pressure depends on thrust (force acting perpendicularly) and
area.
Q. 2 (a) The heat produced due to friction between the meteors and the
atmosphere burn the meteors.
(b) Due to more area, pressure on the shoulder is reduced.
(c) In this case friction is reduced.
(d) Due to less friction.
(e) This increases friction.
(f) In order to increase friction.
(g) Due to less area, pressure is more.
(h) Because heat produced, due to friction.
(i) Friction due to use, causes wear and tear.
(j) Rolling frictions is less than sliding friction.
(k) Oily hand reduces friction.
Q. 3 (a) Electrostatic force
(b) Magnetic force
(c) Muscular force
(d) Gravitational force
(e) Frictional force
Q. 4 (a) (8 + 9) – 6 = 11 N in the direction of 8 N and 9 N.
(b) P =
F
550
550 × 1000
=
=
Pa = 6250 Pa
A
0.044 × 2
44 × 2
F
6
6 × 1000
=
=
= 2000 Pa
A
0.003
3
F
120
2
=
= 0.002 m
(d) A =
P
60000
(c) P =
(e) (700 – 500) N = 200 N along the boat.
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(f) A = 5 × 2 = 10 m2, P = 50 Pa
F = A × P = 10 × 50 = 500 N
(g) F = P × A = 0.05 × 10 × 6 = 3 N
F
1250
=
= 50 Pa
(h) P =
A
25
F
693
2
=
= 23100 N/cm
(i) P =
A
0.03
F
3000 × 9.8
2
(j) A =
=
= 1.96 m
P
15000
Q. 5 (a) False, lesser (more)
(b) False, muscular (gravitational)
(c) False, larger (smaller)
(d)True
(e) False, force (pressure)
(f) False, more (less)
Q. 6 (a) Starts moving
(b) Stops motion
(c) Change in direction
(d) Change in shape and size
Q. 7 (a) Contact force (muscular force)
(b) Contact force (muscular force)
(c) Contact force (muscular force, frictional force)
(d) Non contact force (magnetic force)
(e) Contact force (frictional force)
(f) Contact force (muscular force)
(g) Contact force (impact force)
(h) Contact force (muscular force)
(i) Contact force (muscular force)
(j) Non-contact force (electrostatic force)
Q. 8 (a) Magnetic force—The force exerted by the magnet on magnetic
substances is known as magnetic force.
Electrostatic force—The force developing on non-conductors due
to friction is called electrostatic force.
(b) Pressure—Thrust acting per unit area is called pressure.
Force—It is that physical cause which changes or tends to change
the state of rest or motion of an object or the shape of an object.
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(c) Rolling friction—When a wheel is in contact with a solid surface,
and a force is applied to the wheel, the wheel will start to roll. The
friction that comes into action is rolling friction.
Sliding friction—The frictional force offered when sliding an
object is called sliding friction.
(d) Lubricating—Putting certain substances such as oil and grease
between the moving parts of a machine reduces friction.
Polishing—Making the surfaces, which are in contact, smooth by
polishing them helps to reduce friction.
(e) Streamlining—Making a body ‘boat-shaped’ helps to reduce
friction offered by air or water. Birds, fishes, ships, aeroplanes
etc. have a streamlined shape. This helps them to cut through air
or water easily.
Having treads on tyres—Rougher the surface, the more is the
friction. Hence the tread on tyres of automobiles are designed
suitably to increase its grip on the road.
Q. 9 (a)(ii)
(b)(iv)
(c)(iii)
(d)(i)
(e) (i), (iv)
(f) (i)
(g)(iii)
(h)(iv)
Q. 10 (a)(ii)
(b)(i)
(c) 5 Pa
Q. 11 (a) (40 + 30) N = 70 N
(b) (20 – 20) N = 0 N
(c) No motion
(d) Frictional force
Q. 12 (a) Figure (i) due to more frictional force
(b) Figure (ii)
(c) Figure (ii)
Q. 13 (i)
Chapter 4: Work and Energy
Exercise (pages 62, 63 and 64)
Q. 1 (a) Work is said to be done when the point of a force moves an object
through a certain distance in the direction of the force.
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SI unit of work—Joule (J)
One joule of work is said to be done when a force of 1 newton (N)
moves a body through a distance of 1 metre (m).
(b) If there is no distance moved in the direction of force.
(c) force, displacement
(d) W = F × S
W → Work done , F→ Force, S → Displacement
(e) Energy is the ability or capacity to do work. SI unit →joule (J)
(f) Potential energy—It is the energy possessed by a body by virtue
of its position or configuration (shape).
Kinetic energy—It is the energy possessed by a body by virtue
of its motion.
(g) Body moving fast
(h) Heavy body
(i) Stone which is kept on the top of a tree.
(j) Elastic potential energy, due to change in shape
(k) Dynamo or generator
Q. 2 (a) On 2nd floor
(b) potential energy
(c)Zero
Q. 3 (a) (i) B
(ii) Kinetic energy
(b) Potential energy to kinetic energy.
Q. 4 (a) Potential energy to kinetic energy.
(b) Nail would have gone more in the block.
Q. 5 (a) Potential to kinetic,
(b) Chemical to heat to mechanical
(c) Potential to kinetic
(d) Chemical to heat
(e) Electrical to mechanical
(f) Electrical to sound
(g) Light to chemical
(h) Electrical to light
(i) Electrical to heat
(j) Solar to electrical
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(k) Muscular to mechanical
(l) Electrical to sound.
Q. 6 (a) W = F × S
= 65 × 16
= 1040 J
(b) W = F × S
= 40 ×
= 32 J
80
100
(c) W = F × S
= 30.8 J
= 70 × 44
100
(d) W = F × S
= (600 + 400) × 30
= 30,000 J
(e) W = F × S
⇒ 568 = F × 8
568
= 71 N
⇒ F =
8
(f) W = F × S
⇒ 16500 = 750 × 5
16500
= 22 m
⇒
S =
750
Q. 7 (a)True
(b) False, is done (is not done)
(c) False, heat (mechanical)
(d)True
(e) False, newton (joule)
Q. 8 (a) Potential, kinetic, electrical
(b) Chemical, electrical, electrical, chemical
(c) Sound, electrical
(d) Motion, force
Q. 9 (a)(i), (b) (ii), (c) (i), (d) (iii)
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Chapter 5: Simple Machines
Exercises (Pages 75, 76 and 77)
Q. 1 (a) A simple machine is a tool or a device that helps us to
(i)multiply
(ii) increase the speed of doing work
(iii) apply the force (effort) in a convenient direction
(iv) make the force act at the desired position.
(b) Yes, output work is always less than the input work. In other
words, we have to do more work on the machine then that done
by the machine. This is because some extra work has to be done
in order to overcome friction between the movable parts of the
machine, part of the input work is used up in doing work against
the force of friction and moving the movable parts of the machine.
Thus no machine is 100% efficient.
(c) Input work is the work done by the effort applied. It is the product
of the effort and the distance moved by the effort. This is work
done on the machine.
Output work is the useful work done by the machine. It is the
product of the load and the distance moved by the load.
(d) Class I lever.
(e) A fixed pulley (Figure 5.10 at pg 70 of textbook)
A movable pulley (Figure 5.11 at pg 71 of textbook)
(f) A lever is balanced when the product of the load and the load arm
is equal to the product of the effort and the effort-arm. This is the
principle of lever.
(g) Lever, wheel and axle, pulley, inclined plane, wedge and screw.
(h) Windlass, screwdriver.
(i) An inclined plane is simply a slope used to raise a heavy load by
pushing it up with smaller effort. For example, staircase, ramp
often provided in front of house in order to push a bicycle or
scooter onto the verandah.
(j) A wedge is simply two inclined planes joined together to form a
sharpened edge. It may also have only one inclined surface and
one straight.
A wedge is used to split a solid object into two, like a log of wood,
by inserting the sharp end of the wedge into a crack in the log and
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hammering at the top of the broad end. For example,Axe, knife,
hammer and chisel.
Q. 2 (a) A does (250 × 5) or 1250 J of work
B does (530 × 3) or 1590 J of work
B does (1590 – 1250) J = 340 J of more work.
(b)
(c)
(d)
By increasing effort arm (i.e., distance FE)
For scissor MA < 1, gain in speed is obtained.
For shears MA > 1, force multiplier is used.
An inclined plane has to be used.
Q. 3 (a)
(c)
(e)
(g)
Wheel and axle Lever, (III Class), Lever (III class), Wheel and axle
(b) Inclined plane,
(d) Lever (II class),
(f)Screw,
(h)Wedge.
(b) 10 g
Q. 4 (a)A
(c) part with B
(d) part of A
(e) class I
(f) part with A, having more distance and gaining more moment will
go down.
Q. 5 (a) In the second case (i.e. Y)
(b)(i)True
(ii)False
Q. 6 (a) Figure (b)
(b) Figure (c)
(c) Smaller effort is required.
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Q. 7 (a) (i) 20 ×
=2J
100
1
(ii) 100 × =1J
100
1
(iii)
× 100% = 50%
2
(b) No, as no practical machine is 100% efficient.
Q. 8 (a)
(b)
E
F
E
L
F
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(c)
(d)
F
E
L
F
L
(e) (f)
L
F
L
E
E
E
F
Q. 9 (a)True
(b) False, second (first)
(c) False, pulley (wedge)
(d)True
(e) False, force (speed)
(f)True
(g) False, fixed (movable)
Q. 10 (a)
0.3 m
1.2 m
L
E
MA =
(b)
MA =
MA =
⇒ 20 =
⇒
(c)
F
n =
MA =
⇒
4 =
⇒
E =
E.A
1.2
=
=4
L.A
0.3
L
860
=
= 20
E
43
Effort arm
Load arm
150
n
150
= 7.5 cm
20
L
E
256
E
256
= 64 N
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(d) 75 × n = (20 + 25) × 1.5
⇒ 75 × n = 45 ×1.5
1
= 0.9 m
⇒
n=
100
700 × 3
(e) Efficiency =
× 100
120 × 35
= 50 %
Q. 11 (a) (i) (b)(ii)
(c) (iii) (d)(ii)
(e)(i)
Chapter-6 Magnetism
Q. 1 (a) The phenomenon by which a magnet attracts certain substances
is called magnetism.
(b) Magnetic substances are those substances that are attracted by
magnets. For example, iron, cobalt, nickel, steel etc.
Non-magnetic substances are those that are not attracted by
magnets. For example, rubber, plastic, glass, gold etc.
(c) Four important properties of a magnet are:
(i) Attractive property
(ii) Directional property
(iii) Unlike poles attracts like poles repel.
(iv) Poles exist in pairs.
(d) Activity 3 (Textbook page-80)
(e) Activity 4 and 5 (Textbook page-81)
(f) A piece of iron or steel rod is taken and placed on a wooden table.
A strong bar magnet is taken and the iron rod is stroked with the
bar magnet in only one direction, moving from one end to the
other. Say from (A to B) . Each time, same pole of the magnet is
used. The end of the magnet is drawn along the bar from one end
to the other, raised and then brought back to the starting position.
This process is repeated about forty to fifty times in the same
direction. The iron rod if tested with iron filings will be seen to
possess magnetism. Also it will be seen that end A of the iron bar
will possess the some polarity as the pole being rubbed with it.
We may, also try this method by using a flat steel needle instead
of the iron bar. (See Figure 6.12 of textbook page 83)
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(g) Activity 7 (textbook page 84)
Figure 6.16 (textbook page 84)
(h) Magnetic keepers are simple pieces of soft iron. They are kept in
contact with opposite poles of a pair of bar magnets or across the
poles of a horse shoe magnet. Figure 6.22 (Textbook page 86).
A magnet can be demagnetised by hammering the magnet, by
rough handling, heating the magnet above a certain temperature,
by passing electric current through an insulated wire wrapped
around the magnet for some time.
(i) Increasing the current, increasing the number of turns in the coil.
(j) The end of the bar magnet which points towards the north is called
North pole and the end pointing towards south is called the South
pole.
(k)Lodestone
Natural magnets shape is not proper and strength is weak as
compared to artificial magnets.
(l) We tie one end of a thread around the middle of a bar magnet
and knot it tightly. We tie the other end of the thread to the end
of a foot rules. We insert the free end of the ruler in between two
body lying in a stack placed along the edge of a table. We make
sure that the magnet is hanging freely as shown in the (Figure 6.6 of Textbook page 80). The end which points towards geographic
north is north pole and the end pointing towards geographic south
is south pole.
(m) Uses of electromagnets:
(i) Used in telephones, telegraphs, radios
(ii) Used in cranes to lift large and heavy articles made of magnetic
substances like iron or steel.
(iii) Used to run Maglev trains
(iv) Used in factories to lift heavy iron objects.
(n) A magnetic compass or simply compass is a device used to
determine direction. It is essentially made up of a magnetic needle
which is free to swing about a pivot at its centre. The needle always
comes to rest pointing towards the Earth’s north-south direction.
(o) See Figure 6.4 (Textbook page 79)
Q. 2 (a) A, because it repel. Repulsion is sure test of magnetism.
(b) We bring an electromagnet on the sand mixture, iron filings being
magnetic substance will be attracted on the electromagnet, on
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switching off the current iron filling would drop on a separate
place. Thus sand and iron fillings are separated.
(c) We cannot separate the iron loads from the permanent magnet
in that case an electromagnet is preferred, whose current source
can be switched off and on, then we can separate heavy iron loads
from an electromagnet easily.
(d) Attraction can take place between opposite poles,as well as
between magnets and non-magnets (magnetic substance) but
repulsion always occur between same poles of two magnets.
Hence, repulsion is a surer test of magnetism.
(b)Electromagnet
Q. 3(a)Electromagnet
(c)Plastic
(d)Steel
(e)Demagnetisation
(f)lodestone
Q. 4 (a) False, tin (iron)
(b) False, stainless steel (steel)
(c) False, east-west (north-south)
(d)True
(e) False, the middle part (poles)
Q. 5 1 → N-pole
2 → S-pole
3 → N-pole
4 → S-pole
5 → S-pole
Q. 6 (a) 1 → S-pole
2 → N-pole
(b) 1, 3 → N-pole
2, 4 → S-pole
Q. 7 (a) Iron clip is attracted towards the rod.
(b) Strength increases, more iron clips are attracted.
(c) Strength increases, more iron clips are attracted.
(d) No attraction takes place
(e) An electromagnet.
Q. 8 (a) It becomes a magnet.
(b)A → S - pole
B → N-pole
(c) Plastic being non-magnetic, nothing will happen.
Q. 9 (ii) is correct as N-pole will induce S-pole and vice versa.
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Q. 10 (a) A magnet will attract and repel a magnet will not attract a bar of
brass, will always attract a bar of iron.
(b) A magnetic compass will show polarities of a given magnet by
repulsion, shows no movement for a bar of brass, for iron piece
compass needle do not deflect.
(b)(i)
Q. 11 (a)(iv)
(d)(iii)
(c)(iv)
(f)(iii)
(e)(iii)
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