Heat Energy
Multiple Choice Questions:
1.
What happens to the volume of water when it is heated from 00C
to 100C?
a)
increases b) remains unchanged c) First decreases and then increase d) decreases
2.
What happens to the density of a substance when it is
heated?
a) first
decreases and then increases b) decreases c) increases d) remains unchanged
3.
What is the freezing point of alcohol?
a) -1000C b) -1110C c) 1170C d) -1170C
4.
One Calorie is equals to ………….. Joule.
a) 100 J b) 4200 J c) 1000 J d)
4.2 J
5.
Which of the following has highest value of specific heat
capacity?
a) water b) oil c) alcohol d) iron
6.
a
Answer: 1(c), 2(b), 3(d), 4(d), 5(a),
Very Short Answer Questions: [1 mark each]
- Define
heat, what is its SI unit?
The total
kinetic energy presents in the molecules of a body is called heat. Its SI unit
is Joule.
- What
is one Joule heat?
The amount of heat required to raise the temperature of
water of mass 1kg through 10C is one Joule heat.
- What
is one calorie heat? Mention the relation between.
The amount to heat required for 1gm pure water to raise the
temperature 1°C or 1k is called one calorie heat.
1 calorie = 4.18 joules. =4.2 (approx)
- On
what factors the heat energy depends on?
The heat energy depends on.
(i) Mass of an object.
(ii) K.E. of the molecules present in the object.
- What
is temperature? Write its SI unit.
The average kinetic energy presents in the molecules of a
body is called temperature. Its SI unit is Kelvin (K).
- On
what factors temperature depends on?
The temperature of a body depends on the kinetic energy of
the molecules.
- What
are the effects of heat?
The effects of heat are.
(i) Change in state. (ii)
Rise in temperature (iii) Thermal
expansion. (iv) Chemical change.
(v) Change in solubility.
- Define
thermometer and calorimeter.
The device which is used to measure the temperature of a
body is called thermometer.
The device which is used to measure the amount of heat is
called calorimeter.
- Define
anomalous expansion of water.
When water is heated from 0°C to 4°C the volume of water
contracts instead of its expansion and when it is cooled from 4°C to 0°C, the
volume of water expands instead of contraction, this peculiar character of
water is called anomalous expansion of water.
- What
is liquid thermometer?
The thermometer which contains liquid like mercury or
alcohol based on the principle of uniform change in volume of liquid with the
change in temperature is called liquid thermometer.
- What
is the working principle of thermometer?
The working principle of thermometer is the ‘expansion and
contraction of liquid with the change in temperature’.
- What do you mean by thermal expansion?
The expansion of a substance due to heat is called thermal
expansion.
- What
are the fixed points in a thermometer?
The fixed point in a thermometer are: upper fixed point and
lower fixed point.
- Define
upper fixed point.
The temperature at which pure water boils at normal
atmospheric pressure is called upper fixed point.
- What
is lower fixed point?
The temperature at which pure ice starts to melt is called
under normal atmospheric pressure is lower fixed point.
- Define
specific heat capacity of a substance.
The specific heat capacity of a substance is defined as the
amount of heat gain or loose to change the temperature of unit mass (1 Kg) of
pure water by 10C or 1K.
- State
the principle of calorimeter.
It states that amount of heat gained is equal to amount of
heat lost by a body in a closed system.
- What
is meant by specific heat capacity of water is 4200 J/kg°C?
It means that the amount of heat required for the water of
mass 1k-to raise the temperature 1°C or 1K is 4200j.
- Define
absolute zero.
20. The
temperature of a body at the condition in which the KE of molecules is equal to
zero is called absolute zero. It is equal to -273°C or 0K.
21. On what
factors heat lost or heat gain by a body depends? And mention the relation of
them with heat lost or gain.
The heat gain or lost by a body denend upon: (i) mass of the
body (ii) sp. heat capacity (iii) change in temperature. The amount of heat
gain or lost is directly proportion to all these above mentioned factors.
- What
is heat equation?
23. The
quantity of heat energy gained or lost by an object is product of mass of the
object, specific heat capacity and difference in temperature. (Q = nisdt)
Where.
Q = quantity of heat gained or lost.
M = mass of the object
S = specific heat capacity of the
substance
dt = change in temperature.
- How does the change in volume occur when water is cooled from
10°C to 0°C ?
The volume of water gradually
decreases from 10°C to 4°C due to contraction of molecules but the volume of
the water starts to increase on cooling further below 4°C upto 0°C due to
anomalous expansion of water.
25. Write the
relation of temperature in various scales.
The relation between various scales of thermometer are:
26.
Short answer type questions [2 marks each]
1.
What is the cause of anomalous expansion of water?
Water
molecules are attached to each other by hydrogen bonding. It forms linear
structure in liquid state and has less volume. When water freezes water
molecules form a tetrahedral structure and has more intermolecular space so
that volume increases.
2.
The heat changes the state of body, why? Give reason.
When a
body is heated, the kinetic energy of the molecules increases, intermolecular
force decreases. So that the intermolecular space increases. As a result solid
changes into liquid and liquid into gaseous on heating. Hence the state of a
body changes by heat.
3.
When gases state of a body is cooled it changes into liquid,
furthercooling it changes into solid, why? Give reason.
When
gaseous state of a body is cooled, the kinetic energy of the molecules
decreases, intermolecular force increases. So that intermolecular space
decreases as a result it changes into liquid on cooling by the same process it
changes into solid on further cooling.
4.
Why heat can change the temperature of a body? Give reason.
Heat is
total KE of the molecules present in a body and temperature is average KE of
molecules of a body. On heating KE of molecules increases as a result average
KE of molecules or temperature also increases.
5.
Different quantity of same object can have same temperature but
different heat energy, why? Give reason.
Temperature
is average KE of molecules present in the body so it may be same in different
quantity of matter but heat is total KE of molecules present in the body so it
may be more in a body which has more quantity and less in the body which has
less quantity.
6.
Why does heat cause the expansion of volume of a body?
When a
body is heated, the KE of the molecules of a body increases, intermolecular force
decreases, so that inter-molecular space increases as result heat causes the
expansion of volume of body.
7.
Small gap is kept between the two railway tracks, Why?
When the
trains move on the track with a speed, heat is produced due to friction as a
result the volume of railway track increases, if the gap is not left it bends
and accident may happen. so small gap is kept between two railway tracks.
8.
Electric wires are seen sagging during summer seasons. Why?
During
summer, the surrounding receives more heat from sun so it becomes more hot. Due
to this heat the volume of wires increases as a result electric wires are seen
sagging (looped).
9.
Why the chemical change occurs due to heat?
Heat
increases the KE of the molecules of reactants. So that there becomes more
probability of collision of reactant molecules, on reactant molecules collide
with more force, As we know that the combined chemical reaction occurs due to
collision of reactant molecules, the chemical reaction occurs due to heat,
For
decomposition reaction, we know that heat is released due to formation of bond,
and energy is required for the breaking of bonds, sometime heat provides the
energy to break the bond. So chemical reaction occurs due to heat.
10. Why heat causes the
change in solubility?
Solubility
means amount of solute in gm that can dissolve in 100 gmto form saturated
solution. And while dissolving the solute takes the intermolecular space. When
solvent is heated, the KE of molecules increases intermolecular force
decreases, intermolecular space increases so that solvent can dissolve more solute.
As a result solubility increases, hence heat causes the change in solubility.
11. Water gets solidified
from the top but ghee and honey solidify from bottom, why?
When the
temperature of water decreases, the density of the water continue to increase.
When the temperature water reaches to 4 degree Celsius, the density became
highest. Whereas on further decreases in the temperature of water below 4
degree Celsius, the density of water start to decrease.. At 0 degree Celsius (
i.e ice), the density of water become the lowest 0.9 gm/cm3. Hence, those ice
formed will float on the surface of water forming a layer, due to its low
density. So, water seems to be freezes from top to the bottom.
In
contrast ghee and honey, on the lowering of the temperature, frozen ghee
(solid) and honey acquire higher density than that of liquid form. Hence, ghee
and honey seems to be freezes from bottom to the top.
12. A beaker fully filled
with water at 4°C overflows on heating andcooling, why?
Water has
highest density at 40C and least volume, when it is cooled the
volume increases due to anomalous character of water and further heating again
volume increases due to thermal expansion. So, a beaker fully filled with water
at 4°C overflows on heating and cooling.
13. Aquatic animal can
survive at the bottom although pond is covered with ice. Why?
Due to
anomalous behavior of water. Water has maximum density at 4°C.When the
temperature of surrounding decreases gradually from 4°C to 0°C. there is the
layers of water from 0°to 4°C from top to bottom in ponds as the density of
4°C>3°C>2°C>0°C. So water gets frozen at 0°C. and remain at top as a
result aquatic animal can survive although the pond is covered with ice.
14. Days in desert are very
hot and nights are very cold. Why?
The
specific heat capacity of sand is very low. i.e. 1300J/kg °C. So temperature
raises very fast during day and it cools fasters at nights. As a result days in
desert are very hot and nights are very cold.
15.
Temperature of a small island remains same throughout the year.
Why?
The temperature of a
small island remains the same throughout the year because of the
specific heat capacity of water. Water has a high specific heat capacity, which
means that it takes a lot of energy to change its temperature. The ocean, which
surrounds most islands, has a large mass of water, and therefore a high
specific heat capacity. This means that the ocean can absorb a lot of heat from
the sun without its temperature changing significantly. The air above the ocean
is also warmed by the ocean, and so the temperature of the air above an island
is also relatively constant throughout the year.
16. Newly built quilt is
warmer than older one, why?
Newly
built quilt contains more air molecules, which is bad conductor of heat. It
blocks the flow of heat from body to surroundings. So, newly built quilt is
warmer than old one.
17. Wearing two shirts is
warmer than single jacket, why?
While
wearing two shirts there is air between them, which stops to, flow the more
heat from our body to the surrounding as a result the wearing two shirts is
warmer.
18. Water is used to cool
the engine, why?
Water has
highest specific heat capacity i.e. 4200 j/ kg °C. So it can absorb more heat
from engine with minimal raise in temperature. As a result, the engine of
vehicle remains comparative cooler for a long time. So, water is used to cool
the engine.
19. A metal chair is felt cooler
than a wooden chair during winter, why?
Metal is good conductor of heat so while touching the metal
the heat flows from our body, unlike wooden chair, as it is bad conductor so we
feel more cooler when we touch a metal chair.
20. When a drop of water is
added in boiling oil, it bursts. Why?
When a drop of water added in boiling oil, its temperature
rises very fast so that its kinetic energy sharply increases. Sharp increases
in vibration of water molecules causes it to brust.
21. A beaker at ordinary
glass gets crack when boiling water is poured in it? Why?
Ordinary glass is affected by temperature, when boiling
water is kept. its lower part expands unlike upper part, and so it cracks.
22. A fully filled bottle is
kept in refrigerator to freeze, why?
Water has highest density and least volume at 4°C. So when
temperature becomes 0°C the volume expands as a result a fully filled bottle
with water gets break. So. a fully filled bottle is kept in refrigerator.
23. Some space is left in
the bottle of soft drink, why?
Soft drinks are kept in refrigerator, if the bottle gets
freezed, the water in the bottle gets expanded below 4°C due to anomalous
expansion of water so that extra space left in the bottle maintains the volume
of extra space.
24. Water is used in hot
water bag rather than oil, why?
Water has highest specific heat capacity i.e. 4200 J/kg°C.
So, it remains hotter for longer time so that it can be used in hot water bag
to warm longer but oil has low specific heat capacity Due to having low
specific heat capacity it does not remains hotter for a long time.
25. Perspiration is
necessary during summers, why?
We are warm blooded animal, i.e. temperature of our body
remains fixed i.e. 37°C, during summer the temperature of surrounding becomes
more, so heat flows from surrounding to our body, to keep our temperature
constant perspiration is necessary.
26. Water in earthen pots
remains cool in summer day, why?
Numerous pores are present in the earthen pots, so water
slowly comes out to the surface of pot from inner part and gets vaporized which
prevents the heat energy to flow from surrounding to water, as a result water
inside the pot remains cool.
27. Why does milk boil
faster than water? Give reason.
The milk has less specific heat capacity than water, so the
temperature of milk increases faster on applying equal heat, so the milk boils
faster.
28. Wet clothes are kept at
the forehead of a person suffering from fever, why?
Water has highest sp. heat capacity i.e 4200 j/kg°C. So it
absorbs more heat from our body during fever As a result wet clothes are kept
at the forehead of a person suffering from fever.
29. When we get out of a bed
in the very cold morning we feel the room cold or but when we come back staying some time
outside, we feel the air of room warmer, why?
At first when we are inside the room, we have no comparison
of loose of heat energy as a result we feel cool due to flow of heat from our
body to surrounding.Our body loses more heat energy when we remain outside,
when we get inside the room from outside our body loses comparatively less heat
energy as a result we feel warmer, but at first when we are inside the room, we
have no comparison of lose of heat energy as a result we feel cool.
30. Heat energy contained in
burning matchstick is less than the 5 liter water at 20° C. Why?
Heat is total kinetic energy of the molecules of the
substance so that heat depends on the mass of the object. The mass of the burning
matchstick is less than 5 liter water so that heat energy contained in burning
matchstick less than 5 liter water at 20°C.
31. Temperature below OK or
- 273°C is not possible in this universe, why?
Temperature is the measure of average kinetic energy of the
molecules of a substance. The kinetic energy of the molecules is never be
negative. As a result temperature below 0 K is never possible.
32. Animals curl to ball
during winter, why?
The temperature of atmosphere falls sharply in the winter.
As animals curl to ball, minimum area of the body is exposed out to lose heat
energy from their body that helps to keep them warm. So that animals curl to
ball during winter.
33. Water supplying pipes
burst during winter in cold region, why?
As the atmospheric temperature falls below 4°C the
temperature of water also falls. As the temperature of water falls below 4°C in
fully filled pipelines, the volume of water increases due to anomalous
expansion of water but there remains no extra space for increased volume of
water so that the water provides more outward pressure to burst.
27. Two different metal
balls of equal mass of different specific heat capacity are given equal heat
energy which of them gets heated more and why?
The metal ball with less specific heat capacity gets heated
more because less heat energy is sufficient to increase the temperature of it
by 1°C.
28. Two metal balls with
different specific heat capacity and equal massare heated upto 200°C, which of
them needs more heat and why?
Metal ball with more specific heat capacity absorbs more
heat energy because more heat energy is required for it to change the
temperature.
29. What is the cause of
land breeze?
During nights the lands cools faster due to low specific
heatcapacity and the water of sea remains hotter due to more specific heat
capacity, the air above the sea also becomes hotter and raises up, so that air
from land blows towards the sea.
30. What is cause of sea
breeze?
During days, the land becomes hot faster due to its less
specific heat capacity, so the air particles above land also become hotter and
raise up, but the air above sea remains colder due to more specific heat
capacity of water, as a result air blows from sea to land.
31. If a
person wants to increase the temperature from 16°C to 40°C of 200 kg of water
to have a warm bath, calculate the amount of heat energy required (sp. heat
capacity of water = 4200° j/kg°C)
Here,
Initial temperature (T1)= 16°C
Final temperature(T2) = 40°C
Mass of water (m) = 200 kg
Specific heatcapacity
of water (s) = 4200J/Kg0C
The amount of heat required (Q) = ?
We know that
Q= msdt = ms(T2-T1)
=
Therefore amount of heat required is 2.0 6 x 10 .1.
32. 2.1 x 105
J of heat energy is given to 2 kg object to warm up from 25°C to 50°C.
Calculate its specific heat capacity.
Given:
Amount of heat required (Q) = 2.1×105 J
Mass of object (m) = 2 kg
Initial temperature (T1) = 25°C
Final temperature (T2) = 50°C
Specific heat capacity (s) = ?
We have formula
Q = msdt
or, 2.1 × 105= 2×S(50-25)
or, 2.1 × 105 = 2×25s
or, s =
⸫The specific heat capacity of the substance is 4200J/Kg0C.
33. How much
heat energy is liberated out by two kg iron sphere during cooling from 10°C to
- 12°C. Specific heat capacity of iron is 47OJ/kg°C.
Here.
Mass of iron (m) = 2 Kg
Initial temp (T1) = -12°C Final temp (T2) =10°C Sp. heat
capacity (S) = 470 J/Kg°C
Heat lost (Q) = ?
We have
Heat lost (Q) = ms(T2— TI)
Or, Q = 2 ×470 [10-(-12)]
Or, Q= 2× 470 × 22 = 20680 Joules.
Hence amount of heat lost by iron ball = 20680 J.
34. 70 KJ of
heat energy is lost by 2 kg iron sphere when cooled down from 90°C to 15 °C.
Calculate its specific heat capacity.
Here, Amount of heat (Q) = 70 KJ
= 7 x 104Joule.
Mass of iron (m) = 2Kg,
Initial temperature (T1) = 90°C
Final temperature (T2) = 15°C
Specific heat capacity (S) = ?
We have
Q = msdt
Or, 7× 104 = 2×S(90-15)
Or, S=
S=466.66 J/Kg°C.
Hence the Sp. heat capacity of iron = 466.66 J/Kg°C.
35.
A person
drinks 250 g of cold drink at 7°C. Calculate the heat lost from the body of the
person. Specific heat capacity of cold drink is 3500 J/kg°C.
Here,
Mass of cold drink (m) = 250g = 0.25 Kg Initial temp (T1) =
7°C
Final temp (body temperature) (T2) = 37°C
Specific heat capacity (S) = 3500 J/Kg°C
Heat lost (Q) = ?
We have,
Q = ms (t2—t1)
Or, Q=0.25×3500 x(37-7)
Or, Q =0.25×3500×30 = 26250 Joule.
⸫Heat lost from his body is 26250 J.
36.
A liquid
is at 37 °C. It is heated up to 67°C temperature. Calculate heat absorbed by
the liquid of 250 g mass. Specific heat capacity of liquid is 3800 JIkg°C.
Here,
Specific heat capacity. (S) = 3800 J/Kg°C
The initial temperature (T1) = 37°C
Final temperature (T2) = 67°C
Mass (m) = 250 gm. = 0.25 kg.
Amount of heat gain (Q) = ?
We have,
Q = ms (T2 - T1) = 0.25×3800 (67 —37)
Or Q = 0.25×3800×30 = 28500 Joule.
37.
Very Long Answer type questions [4 marks
each]
1.
Observe the given curves and answer the following questions.
It
explains the change in volume of water on changing temperature from 0°C to its
boiling point.
(ii)
What does figure (b) explain?
It explains
the change in density of water on changing temperature from 0°C to its boiling
point.
(iii)
What is the density of liquid in figure (b) at 4°C?
The
density of liquid in figure b is maximum at 4°C.
(iv) Write an
advantage of this phenomenon.
The
advantages of this phenomenon are:
Aquatic
animals remain alive in water although the water on the surface is frozen.
2.
Write
four advantages of anomalous expansion of water.
Ans: The
advantages of anomalous expansion of water are given below.
(i)
The aquatic animal can survive even after the pond is
covered with ice in cold region.
(ii)
The frozen ice over the river and sea acts as natural
bridge.
(iii)
It maintains moderate temperature inside large water bodies.
(iv)
The anomalous expansion of water helps to erode rocks and
soil. When water freezes, it expands and can break apart rocks and soil. This
helps to create new landforms and deposit sediments in new places.
1.
Three metal balls of the same mass having different specific
capacityx, y, z are given in the table below.
Answer the
following questions on the basis of given table.
|
Metal |
Sp.
heat capacity |
|
X |
450
J/kg°C |
|
Y |
500
J/kg°C |
|
z |
140
j/kg°C |
(i)
Which one will have more temperature if all of them are
heated with I0000J heat? Why?
The metal
z will have more temperature because it has least specific heat capacity (140J/kg°C).
Since specific heat capacity is inversely proportional to the change in
temperature i.e. Sα
(ii)
Which of them cools faster, heating up to 200°C temperature
and placed separately, why?
The metal
z cools faster as we know that heat lost by a body is equal to heat gain, when
it is heated up to 200°C. It is because
it has less specific heat capacity. As we know that specific heat capacity is
inversely proportional to the change in temperature i.e.
(iii)
Which metal penetrates to the greatest depth when each
metallic ball of the given metals are kept on the wax slab after heating them
to 2000C?
Substance
Y penetrates to the greatest depth when each of the metallic balls of the given
metals are kept on the wax slab after heating them to 2000C because
amount of heat contained in a body is directly proportional to the specific
heat capacity i.e. Q α s when mass (m) and temperature (t) are kept
constant. Therefore more the specific
heat capacity, more is the heat contain in a body. Thus, the metallic ball Y
releases more amount of heat among the three metals and hence it can penetrates
to the greatest depth.
(iv)
If the equal masses of the above metals are heated from 1000C
to 2000C, which will require more heat, why?
The amount
of heat require to gain the temperature is directly proportional specific heat
capacity i.e. Q α s when mass (m) and difference in temperature (dt) are
constant. Here, the metal Y has highest specific heat capacity therefore it
needs more heat to increase its temperature from 1000C to 2000C
if the equal masses of the above metals are heated.
2.
Specific heat capacities of three different metals are given
in the tablebelow. Answer the following questions.
|
Metal |
Sp.
heat capacity |
|
A |
910
J/kg°C |
|
B |
380
J/kg°C |
|
C |
470
J/kg°C |
(i)
Which metals will have more temperature, if all the three
metals with same mass and same initial temperature are given 5000 J of heat
energy and why ?
The metal
‘B ‘will have more temperature if all the three metals with same mass and same
initial temperature are given 5000J of heat energy. This is because specific
heat capacity is inversely proportional to the change in temperature i.e.
(ii)
Which metal will penetrate to the maximum depth if all of
them with equal mass are heated upto 100°C and placed on wax slab and why?
Metal A
will penetrate to the maximum depth if all of them with equal mass are heated
upto 1000C and placed on wax slab. The amount of heat contained in a body is
directly proportional to the specific heat capacity. Since metal A has highest
specific heat capacity so it releases large amount of heat for a longer time
and thus penetrate to maximum depth.
i)
What do you mean by the specific heat capacity of metal B is
380J/kg°C?
The
specific hat capacity of metal B is 380J/Kg0C means that metal B
need 380 J of heat energy to raise its temperature through 10C.
3.
If three different substances A, B and C having equal mass
are takenin equal sized vessel and exposed in sunlight. The increased
temperature of A, B and C is given in the table below. Answer the following questions.
|
Substance |
Raised
temperature |
|
A |
5°C |
|
B |
20°C |
|
C |
12°C |
(i)
Which substance has highest specific heat capacity and why?
Substance
A has the highest specific heat capacity. This is because its temperature is
least among A, B and C as specific heat capacity is inversely proportional to
the change in temperature when amount of heat and mass remain constant.
(ii)
The substance A, B and C are let to cool after heating upto
50C, which one of them cools faster and why?
The
substance B will cooler faster as its change in temperature is highest among
the three substances. As its specific heat capacity is lowest among all, its loses
heat significantly faster than A and C.
(iii)
Which of them will be suitable to make thermometric liquid,
why?
Substance
B will be suitable to make thermometric liquid since it has least specific heat
capacity and its expansion will be faster as compare to other two.
4.
Differentiate between heat and temperature.
|
Heat |
Temperature |
|
1. The total kinetic energy present in the molecules of a
body is heat. |
1. The average kinetic energy present in the molecules of
a body is temperature. |
|
2.Its SI unit is joule. |
2. Its Si unit is degree Kelvin. |
|
3.It is measured by calorimeter. |
3.It is measured by thermometer. |
|
4.It is cause of temperature. |
4.It is the effect of heat. |
Here,
Heat required
(Q) = 433.2 KJ = 4.33 x 105 Joule.
Mass of
copper (m) = 2kg
Initial
temperature (T1) = 30°C
Final temperature
(t2) = 600°C
Specific
heat capacity (S) =?
We have,
Q = ms(T2-
TI)
Or4.33×105=
5×S(600-30)
Or S=
6.
10 Kg of water at 45°C is mixed with 20 kg water at 10°C in
winter to take a bath, find the final temperature of the water.
Here,
Mass (m1)
= 10 kg
Mass (m2)
= 20 kg
Temperature
ofm1(t1) = 45°C
Temperatureof
m2 = 10°C
Specific
heat capacity of water = S (let)
Final temp
(t) = ?
We have.
Heat lost
= heat gained
Or, m1
(45 - t) = m2s (t— 10) [⸪ both the substance is water)
Or. 10 (45
- t)= 20 (t - 10)
Or, 45—t =
2t-20
Or, 3t = 65
Or, t =
Therefore,
the final temperature of water is 21.670C.
7.
An iron ball of 2kg with temp 200°C is kept in the water of
mass 20kg of temp 20°C, what will be the final temp of the mixture if Sp. heat
capacity of iron = 470 J/kg°C and Specific heat capacity of water = 4200 J/kg°C?
Here,
Mass of
iron ball (m1) =2kg
Temperature
of iron ball (t1) = 200°C
Specific
heat capacity (S1) = 470 J/kg°C
Mass of
water (m2) = 20kg
Temp of
water (t2) = 20°C
Sp. heat
capacity(S2) = 4200 J/kg°C
Final temp
(t) = ?
According
to the principle of calorimetry,
Heat lost
by iron ball (Q1) = heat gained by water (Q2)
Or, m1S1(t1-t)
=m2S2(t-t2)
Or,
2×470(200-t) = 20×4200(t-20)
Or, 940
(200-t) = 84000(t-20)
Or, 94(200-t)
= 8400(t-20)
Or,
18800-94t = 8400t-168000
Or,
8400t+94t = 18800+168000
Or, 8494t
= 186800
Or t =
⸫ Final
temperature of mixture is 220C.
8.
What will be the quantity of heat required to raise the
temperature of 2 kg paraffin by 1°C. If 44000 J of heat energy is required to
raise the temperature of 1Kg paraffin by 20°C.
Here,
Heat
required t (Q) = 44000J = 4.4×104J.
Mass (m1)
= 1kg
Change in
temp (dt) = 20°C
Sp. heat
capacity (s) =?
We have
formula
Q=m1sdt
Or, 4.4×104=1×S×20
Or, S =
Again,
Amount of
heat (Q') =?
Sp. heat
capacity (S) = 2200 J/kg°C
Mass (m2)
=2 kg
Change in
temp dt = 1°C
Using
formula, Q’ =m2sdt
Q=2×2200×1
4400 J
9.
The specific heat capacity of an object is 1Calorie/g0C.
Convert it in to SI system.
Ans:
Given,
Specific
heat capacity = I cal/g0C
=
=
4200J/kg°C
15. The specific heat capacity of an
object is 5 x 106 erg/gm°C. Convert into SI system.
Ans: Given,
Ans: Given,
Specific
heat capacity = 5 x l06 erg/gm0C
Here 1 erg
= 1×10-7J
⸫ 5×106
erg = 5×106×10-7/10-3
= 500J/kg°C
16. 10kg water is at 12°C. An electric immersion heat or of 48 watt runs for 10mm. Calculate its final temperature. (specific heat capacity of water (S) = 4200J/kg°C) Ans: Given, mass of water (m) = 10kg Specific heat capacity (S) = 4200J/kg°C Initial temperature T1) 12°C
Final
temperature (T2) ?
Power (P)
= 48 watt
Time taken
(T) = 10 min = 600sec. We know that.
- workdone
or energy converted - time taken
energy
converted or. 48 = 600
energy
converted (Q) = 28800J. Now, according to the heat equation. Q=Msdt
28800 = 10
>. 4200 x (12 - 12) or. 28800 = 42000T —504000 or, 28800 + 504000 = 42000T2
or, 532800 = 42000T2
or,
12.68°C = T
Final
temperature of water is 12.68°C
2kg
pressure cooker has 4kg water at 12°C. How much heat energy is required so that
the temperature of the system is 55°C. Specific heat capacity of alloy of
pressure cooker is l000JIkg°C & water is 4200J/kg°C.
Ans: Case
of pressure cooker
Mass (M) =
2kg
Initial
temperature (T1) = 12°C
Final
temperature (T2) 55°C
Heat
gained (Q) =?
Specific
heat capacity (S) = 1000J!kg°C Difference in temperature NO = 43°C We know
that,
Q = msdt = 2 x 1000 x 43 = 86000J Similarly,
Case of
water
Mass (M) =
4kg
Specific
heat capacity (S) = 4200J!kg°C Initial temperature (Ti) = 12°C
Final
temperature (T2) 55°C
Difference
in temperature (dt) = 43°C We know that,
Qi = msdt
= 4 x 4200
x 43
= 722400J
The total
heat supplied = Heat gained by water - heat gained by cooker
=(722400
+86000)1
= 808400J
What do
you mean by the statement that the specific heat capacity of mercury is 138 J/Ikg°C?
How much heat energy does mercury require to increase the temperature of 2 kg
mercury by 50°C?
10 kg
water is at 5°C mixed with 5 kg water at 50°C. Calculate the temperature of
mixture. (Practice Yourself)
Answer the
following questions on the basis of the given diagram.
i) Name
the instrument and mention its one use.
The
instrument is clinical thermometer and it is used to measure the temperature of
human body.
ii) Name
A, B and C.
Name of A
is bulb, B is constriction or kink and C is capillary tube.
iii) Write
the function of B.
The
function of B (kink) of thermometer is to avoid the back flow of mercury from
the capillary tube when the thermometer is removed from the body of a patient.
iv) How is
it differ from digital thermometer?
A clinical
thermometer measures the temperature on the basis of expansion of mercury while
a clinical thermometer works on the basis of thermistor having resistance that
changes significantly with temperature.
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