 CLASS
VII Science (Physics)
Chapter- Heat and Temperature
Question with
solution Part-1
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Q.1. What is heat?
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Ans: Heat is form of energy
that produces feeling of hotness. It is measured in Joule . Calorie is used
to measure energy value of food. 1 cal. =4.2 joule
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Q. 2.What is energy?
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Ans: Energy is capacity to do
work. Energy is neither created nor destroyed it can only changed one form to
another.
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Q. 3.What are the effects of
heat?
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Ans: Heat cause many
change in living and non living thing. They are
1. Heat increase in temperature
2. Heat expand a
substance
3. Heat changes the
state
4. Heat bring chemical change
5.Heat effect living thing
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Q.4. What is temperature?
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Ans: The degree of hotness and
coldness of a body is called temperature of body. Thermometer is an
instrument used to measure temperature. It is work on principle of expansion
in liquid on heating. It is measured in Celsius and Fahrenheit
scale but for scientific work Kelvin scale is used.
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0F = (9/5
x 0C) +32 and oC = (9/5)(F- 32) and K=
C + 273o
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Q. 5.What is thermometry?
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Ans: The science of
measurement of temperature is known as thermometry
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Q.6. What are different types
of thermometer?
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Ans: Thermometer: It
consist of long narrow glass tube having fine bore.There is a glass bulb
filled with liquid mostly mercury at the one end and sealed at other end.
There is small bend just above bulb called Kink. it does not allow
the mercury to fall as soon as taken out from our mouth.
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(i). Laboratory Thermometer:
It ranges from -10oC to 110oC
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(ii) Clinical thermometer: It
is used to measure body temperature. It ranges from 35oC to 42oC
and 94oF to 108oF. Mercury thermometer can
measure temperature from -35oC to 357oC.
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(iii) Alcohol
thermometer used to measure temp. from -125oC to 50oC.
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Q. 7.What is the use of
the m a x i m u m - m i n i m u m thermometer?
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Ans: The maximum and
minimum temperatures atmosphere reported in weather reports which is measured
by a thermometer called the m a x i m u m - m i n i m u m thermometer.
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Q.8. What is the normal body
temperature?
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Ans: 37oC or 98.6oF.
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Q.9. Why mercury preferred
in thermometers?
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Ans: Mercury used due to
following reasons
(i) It expand
uniformly
(ii) It does not stick to wall
(iii) It is shiny and
easy to see
(iv) It remain liquid at
room temperature.
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Q.10. Find at what temperature
measurement on Celsius equal to Fahrenheit.
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[Ans: - 400]
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Q.11. Find at what temperature
measurement on Fahrenheit double of Celsius
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[Ans: 1600]
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Q. 12.What is thermal
expansion (enlargement)?
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Ans: The expansion produced in
substance on heating is called thermal expansion. When we heat a substance
its molecules gain energy and start vibrating rapidly and spread out . As a
result a substance expands.
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Q.13. Why does gas expand more
than solid and liquid?
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Ans: Gas expands more than
solid and liquid because its molecules are bound with very weak force of
attraction.
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Q.14. A bimetallic strip made
of brass and iron welded together. When it is heated, the strip bend why?
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Ans: Brass expand and contract
more than iron on heating and cooling. This unequal expansion and contraction
bent the strip.
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Q. 15.The same quantity of
heat supplied to same amount of different substances does not
necessarily produce the same increase in temperature. Why?
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Ans: Different substances
absorb differently that depends on
(a) Mass of body
(b) change in temperature
(c) Nature of substance. For
this reason the same quantity of heat supplied to same amount of
different substances does not necessarily produce the same increase in
temperature
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Q.16. If difference in
temperature between A and B is 50C , What is the difference in
Kelvin?
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Ans: 5K
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Q.17. Give some examples
expansion causes problems?
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Ans (i). Gaps are left between
two sections of railway tracks that allow expansion in summer and protect
from bending causing accident.
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(ii). During summer, iron
expands and cause serious accidents. To allow this expansion Space left
between two sections of rail tracks.
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(ii). When we pour hot liquid,
sometime glass tumbler crack because inner wall get heated quickly and expand
than outer wall. A Pyrex glass resist from this unequal expansion.
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Q. 18.Explain one good
use of expansion:
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1. In fire alarm expansion put
in good use. The alarm contains two strips of iron and brass bolted together.
When it is heated because of fire, brass expands more than iron and bends
towards iron. Bell starts ringing. As the fire put out strip gets cooled and
straighten again.
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Q.19. What is heat capacity?
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Ans: The amount of heat
required to raise temperature of a substance by 10C . It is
different for different substance. It depends on (a) Mass of body (b) change
in temperature (c) Nature of substance. Q µ m and
Q µ t Þ Q = S m t
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Here, S is a constant and
named Specific heat of body.
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Q. 20.What is specific heat
capacity?
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Ans. The amount of heat
required to raise the temperature of 1 kg by 10C . Water has
highest heat capacity. SI unit is j/kg0C
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Q.21. Define melting and
boiling point
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Ans .The temperature at which
solid melts is called Melting point. Melting point of ice is 00C
and wax is 630 C. The temperature at which liquid changes
into vapour is called boiling point.
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Q. 22.What is latent heat of
fusion?
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Ans: Latent heat or hidden is
amount of heat that only change state not temperature.
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The amount of heat required to
melt 1 kg substance from solid to liquid without change of temperature is
called latent heat of fusion.
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Q. 23.What is latent heat of vaporization?
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Ans: The amount of heat
required to change 1 kg substance from liquid to vapour state without change
of temperature is called latent heat of vaporization.
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Q. 24.Why stem burn more than
boiled water?
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Ans: Because stem has more
latent heat than boiled water[ about 2260j/g]
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Q.25. why does water used as
coolant in car?
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Ans: Water has high
specific capacity this makes water to take long time to heat up by absorbing
very large quantity of heat. Therefore water used as coolant in car and
factories.
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Q.26. What are different mode
of transfer of heat?
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Ans: Heat flows from higher to
lower temperature till both body attend same temperature.
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There are three mode of
transfer of heat
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(a) Conduction: The mode of
transfer of heat from molecules to molecules without movement of particles..
Conduction takes place in solid as its molecules ate closely packed. Solids,
metals and alloy are good conductor. Non metals, plastic glass are bad conductor
of heat.
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(b)Convection: The mode of
transfer of heat from molecules to molecules with movement of particles. In
liquids and gasses heat transferred by convection as molecules are far apart
from each other .
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(c) Radiation: The mode of
transfer of heat that does not require any material medium. Heat of sun reach
the earth by radiation.
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Q.27. At what factor heat
absorbed on radiation by body depends on?
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Ans: (a) Distance between body
and source of heat
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(b) its colour(Black coloured
surface absorb more than white surfaces)
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Q. 29. A desert is very hot in
the day and very cold at night?
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Ans: Due to low specific heat
capacity air above land heated up quickly in the day and cooled quickly at
night. For this reason a desert is very hot in the day and very cold at
night.
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Q.30. Describe construction
and working of thermos flask.
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Ans: thermos flask is doubled
walled glass vessel. Air inside glass wall prevents conduction and
convection. Glass walls are silvered on the inside. Silver is good reflector
of heat this prevent heat loss due to radiation. If we remove the silvering
thermos flask not keep liquids hot or cold for quite a long time.
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