Class-7 Science, Chapter-4 Heat, Additional exercises in line with NCERT book / CBSE Syllabus
Chapter
4
Heat
Additional Exercises
Exercises from textbook
Activities/Projects
Additional Exercises
Choose the correct
answer:
1. The liquid used in thermometer is
a. Alcohol
b. Mercury (✓)
c. Water
d. Eather
2. We wear woolen clothes in winter because
a. They produce heat
b. They are bad conductors of heat (✓)
c. They transform heat
d. They are conductors of heat
3. Heat from the sun reaches earth by
a. Conduction
b. Convection
c. Radiation (✓)
d. None of these
4. Heat transfer by conduction takes place in
a. water
b. Iron (✓)
c. Air
d. all the above
5. SI unit of heat is
a. Calorie
b. kilo calorie
c. Joule (✓)
d. Kelvin
6. A measure of degree of hotness of an object
is called:
a. Temperature (✓)
b. Heat
c. Conduction
d. Heater
7. Clinical thermometer is used to measure our
body temperature. The range of this thermometer is from
a. 35oC to 42oC (✓)
b. -10oC to 110oC
c. -25oC to 40oC
d. 0oC to 100oC
8. The range of laboratory thermometer is
usually from;
a. 35oC to 100oC
b. -10oC to 110oC (✓)
c. -25oC to 40oC
d. 0oC to 100oC
9.
Heat
transfer by convection occurs in
a.
Solids
b.
Liquids
c.
Gases
d.
Both
b and c (✓)
10. When heat falls on some object, which of the
following phenomenon occurs?
a. Reflection of heat
b. Absorption of heat
c. Transmission of heat
d. All the above (✓)
11. The temperatures reported in weather reports
are measured by
a. Clinical thermometer
b. Laboratory thermometer
c. Maximum- Minimum thermometer (✓)
d. None
of the above
Match the column
A
|
B
|
Heat
|
Energy
obtained from food
|
Joule
|
Liquid
used in thermometer
|
Calorie
|
Form
of energy
|
Mercury
|
SI
Unit of heat
|
Ans-
A
|
B
|
Heat
|
Form of Energy
|
Joule
|
SI Unit of heat
|
Calorie
|
Energy obtained from food
|
Mercury
|
Liquid uses in
thermometer
|
Fill in the blanks:
1-
A
reliable measure of the hotness of an object is its temperature.
2-
There
is an increase in volume of gas on heating.
3-
Heat
transfer in liquids takes place by convection.
4-
A thermos is made in such a way that transfer
of heat can be reduced by conduction, convection and radiation.
5-
Substance
expands on heating while contracts on cooling.
6-
Heat
is a form of energy.
7-
No
medium is required for heat transfer by radiation.
8-
In
solids, generally heat is transferred by the method of conduction.
Give One Word:
1-
The
process ot transfer of heat in a solid when molecules transfer heat to their
neighbouring molecules.
Ans- Conduction
2-
The
materials which allow heat to pass
through them easily.
Ans- Conductors
3-
The
materials which do not allow heat to pass through them easily.
Ans- Insulators
4-
The
normal temperature of human body.
Ans- 370C
5-
A
device used to measure temperature.
Ans- Thermometer
State whether the
following statements are true or false:
1-
Heat
flows from cold body to hot body. (False)
2-
Heat
transfer takes place by three methods, conduction, convection and radiation. (True)
3-
When
the temperature of two bodies becomes same the transfer of heat stops. (True)
4-
Our
sense of touch is always a reliabel guide to the degree of hotness of an
object. (False)
5- Air and water are poor conductors of heat. (
true)
6- What we call as normal body temperature is
the average body temperature of a large number of healthy persons. (True)
Select the odd one
(1) air, water, ebonite, iron (poor conductors of heat)
(2) aluminium, iron, wood, copper (good conductors of heat)
Differentiate between
(a)
Sea
breeze and Land breeze
(b)
Conduction,
Convection and Radiation
Sea breeze and Land
breeze
Sea
breeze
|
Land
breeze
|
The cooler air from the sea is called the
sea breeze.
|
Air from the land is called the land breeze.
|
The cool sea breeze blows during the daytime.
|
The cool land breeze blows during the night
time.
|
Conduction, Convection
and Radiation
Conduction
|
Convection
|
Radiation
|
The process by which heat is
transferred from the hotter end to the colder end of an object is known as
conduction.
|
The process in which heat is transferred
by the motion of molecules of fluids (liquids and gases) is known as
convection.
|
The process in which transfer of heat
takes place by electromagnetic waves without involvement of particles is
known as radiation.
|
It requires the presence of medium.
|
It requires the presence of medium.
|
It does not require the presence of
medium.
|
It is a slow process.
|
It is faster process.
|
It is the fastest process.
|
Answer the following
questions:
Q. You are given a choice
in winter of using either one thick blanket or two thin blankets joined
together. What would you choose and why?
Ans- If given a choice, I
would use two thin blankets joined together. There would be a layer of air in
between the blankets which will prevent the flow of heat from the body to the
cold surroundings. Two thin blankets joined together will be warmer than one
thick blanket.
Q. Is it possible to construct
buildings that are not affected much by heat and cold outside? How?
Ans- Yes, it is possible to
construct buildings that are not affected much by heat and cold outside by
1.
Constructing outer walls of buildings so that they have trapped
layers of air.
2.
Using hollow bricks for construction.
Q. Heat from the sun cannot reach
us by conduction or convection as there is no medium such as air in
most of the space between the Earth and the Sun. How does the heat from the sun
reach us?
Ans- From the sun, the heat
comes to us by a process known as a radiation. The transfer of heat by
radiation does not require any medium.
Q. Light a candle. Keep
one hand above the flame and one hand on the side of the flame. Do your hands field equally hot? If not, which
hand feels hotter? Why?
Ans- No, both of our hands,
do not feel equally hot. Towards the top, the air gets heated by convection.
Therefore the hand above the flame feels hot. On the sides, however, there is
no convection and air does not feel as hot as at the top.
Q. How does the heat
travel in the air?
Ans- The air near the heat source gets hot and
rises up. The air from the sides come in, to take its place. In this way air
gets heated. This mode of heat transfer is known as convection.
Q. How does the water get
heated up?
Ans- When water is heated,
the water near the flame gets hot. Hot water rises and the cold water from the sides
moves down towards the source of the heat. This water also gets hot and rises
and water from the sides moves down. This process continues till the whole
water gets heated. This mode of heat transfer is known as convection.
Q. Why does the mercury
not fall or rise in a clinical thermometer when taken out of the mouth?
Ans- There is a kink near
the bulb of clinical thermometer. It prevents mercury level from falling on its
own. Therefore, the mercury level does not fall or rise in the clinical
thermometer when taken out of the mouth.
Q. List the precautions
to be observed while reading a clinical thermometer.
Ans- Following precautions
should be observed while reading a clinical thermometer.
(1)
Thermometer
should be washed before and after use, preferably with an antiseptic solution.
(2)
Mercury
level should be below 35oC before use.
(3)
While
reading the thermometer, level of mercury should be along the line of sight.
(4)
Handle
the thermometer with care. It can break on hitting against some hard object.
(5)
Don’t
hold the thermometer by the bulb while reading.
Q. Draw the diagram of
clinical thermometer. Explain its structure.
Ans-
A clinical thermometer
consists of a long, narrow, uniform glass tube. It has a bulb at one end. This
bulb contains mercury. Outside the bulb, a small thread of mercury can be seen
to get the reading of temperature.
Give reason. Why?
Q. Woolen clothes keep us
warm in winter.
Ans- Wool is a poor
conductor of heat. There is air trapped in between the wool fibres. This air
prevents the flow of heat from our body to the cold surroundings. So, we
feel warm in woolen clothes.
Q. We feel more
comfortable wearing light-coloured clothes in the summer.
Ans- Light colour clothes
reflect most of the heat that falls on them. Therefore we feel more comfortable
wearing them in summer
Q. We feel more
comfortable in dark coloured clothes in the winter.
Ans- Dark surfaces absorb
more heat. Therefore, we feel comfortable with dark-coloured clothes in the
winter.
Q. The windows of the
houses in coastal areas are made to face the sea.
Ans- In coastal areas land
gets heated faster than water during the daytime. The air over the land becomes
hotter and rises up. The cooler air from the sea rushes towards the land to
take its place. The air from land moves towards the sea to complete the cycle.
To receive the cooler sea breeze, the windows of the houses in coastal
areas are made to face the sea.
Q. You are advised to use
an umbrella when you go out in the sun.
Ans- When heat
falls on some object, a part of it is reflected, a part is absorbed and a part
may be transmitted.
We are advised to use umbrella when
we go out in the sun because umbrella protects us from the heat of sun by
partially reflecting the heat radiations.
Q. We should avoid
keeping the clinical thermometer in the sun or near a flame.
Ans- The clinical
thermometer is designed to measure the temperature of human body only. This
thermometer has the range of 35oC to 42oC. It may break
in the sun or near a flame.
Q. The metallic pan for
cooking has a plastic or wooden handle.
Ans- Plastic and wood are
poor conductors of heat. Therefore, metallic pan for cooking has a plastic or
wooden handle.
Exercises from Textbook
Q. State similarities and
differences between the laboratory thermometer and the clinical thermometer.
Ans- Similarities between the
laboratory thermometer and the clinical thermometer-
1-
Both consists
of long, narrow, uniform glass tube.
2-
Both have a
bulb at one end.
3-
Both contain
mercury in the bulb.
Differences between the laboratory and
clinical thermometer-
Laboratory Thermometer
|
Clinical Thermometer
|
Range of laboratory thermometer is
-10oC to 110oC.
|
Range of clinical thermometer is 35oC
to 42oC.
|
There is no kink in laboratory
thermometer.
|
There is a kink near the bulb of
mercury in clinical thermometer.
|
Laboratory temperature is used to
measure temperature in laboratory.
|
Clinical thermometer is used to
measure the body temperature.
|
Q. Give two examples each
of conductors and insulators of heat.
Ans- Conductors of heat-
1)
Iron
2)
Aluminium
Insulators of heat-
1)
Plastic
2)
Wood
Q. Fill in the blanks:
1) The hotness of an object is
determined by it’s temperature.
2) Temperature of boiling water cannot
be measured by a clinical thermometer.
3) Temperature is measured in degree celcius.
4) No medium is required for the
transfer of heat by the process of radiation.
5) A cold steel spoon is dipped in a
cup of hot milk. It transfers heat to its other end by the process of conduction.
6) Clothes of dark colours
absorb heat better than clothes of light colours.
Match the following:
A
|
B
|
Land breeze blows during
|
Summer
|
Sea breeze blows during
|
Winter
|
Dark coloured clothes are preferred
during
|
Day
|
Light coloured clothes are preferred
during
|
Night
|
Ans-
A
|
B
|
Land breeze blows during
|
Night
|
Sea breeze blows during
|
Day
|
Dark coloured clothes are preferred
during
|
Winter
|
Light coloured clothes are preferred
during
|
Summer
|
Q. Discuss why wearing
more layers of clothing during winter keeps us warmer than wearing just one
thick piece of clothing.
Ans- When we wear more layers of
clothing, air gets trapped between these layers, which acts as an insulator. It
does not allow body heat to escape out. Therefore wearing more layers of
clothing during winter keeps us warmer than wearing just one thick piece of
clothing.
Q. Look at the given figure
and mark where the heat is being transferred by conduction, by convection and
by radiation.
Ans-
Q. In places of hot
climate it is advisable that the outer walls of houses be painted white.
Explain.
Ans- White colour reflects most of the
heat that falls on it. It prevents an object from heating up fast. Therefore,
in places of hot climate, it is advisable that the outer walls of houses be
painted white.
Q. Choose the correct
alternative:
1. One litre of water at 30oC is
mixed with one litre of water at 50oC. the temperature of the
mixture will be
a) 80 oC
b) more than 50 oC but less than 80
oC
c) 20 oC
e. between 30 oC and 50 oC
(✓)
2. An iron ball at 40 oC is dipped in
a mug containing water at 40 oC. the heat will
a) flow from iron ball to water
b) not flow from iron ball to water or from
water to iron ball (✓)
c) flow from water to iron ball
d) increase the temperature of both
3. A wooden spoon is dipped in a cup of ice
cream. its other end
a) becomes Cold by the process of conduction
b) becomes Cold by the process of convection
c) becomes Cold by the process of radiation
d) does not become cold (✓)
4. Stainless steel and are usually provided with
copper bottoms. the the reason for this could be that
a) copper bottom make the pen more durable
b) such pen appear colourful
c) copper is a better conductor of heat than the
stainless steel(✓)
d) copper is easier to clean than the stainless
steel
Extended learning- Activities and
Projects
1. Go to a doctor or your nearest health centre.
observe the doctor taking temperature of patients. Enquire:
a. Why does she dip the thermometer in a liquid
before use?
b. Why the thermometer is kept under the tongue.
c. Whether the body temperature can be measured
by keeping the thermometer at some place other than the mouth.
d. Whether the temperature of different parts of
the body is the same or different.
You
can add more questions which come to your mind.
2. Go to a veterinary doctor ( a doctor who
treats animals). Discuss and find out the normal temperature of domestic
animals and birds.
3. Wrap a thin paper strip tightly around an
iron rod. Try to burn the paper with candle while rotating the iron rod
continuously. Does it burn? Explain your observation.
4. Take a sheet of paper. Draw a spiral on it as
shown in the figure. Cut out the paper along the line. Suspend the paper as
shown here above a lighted candle. Observe what happens. Think of an
explanation.
5. Take two similar transparent glass bottles
having wide mouths. Put a few crystals of potassium permanganate or for a few
drops of ink in one bottle. Fill this bottle with hot water. Fill the other
bottle with water. Cover the cold water bottle with a thick piece of paper such
as a postcard. Press the postcard firmly with one hand and hold the bottle with
the other hand. Invert the bottle and place it on top of the hot water bottle.
Hold both the bottles firmly. Ask some other person to pull the postcard. Observe
what happens. Explain.
Did you know?
|
The Celsius scale was
devised by a Swedish astronomer, Anders Celsius in 1742. Strangely, he
fixed the temperature of the boiling water at 0oCelsius and of
freezing water at 100o Celsius. However this order was reversed
very soon.
|
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