Heat:
Heat is a form of energy which gives sensation of warmness. Heat is also defined as the sum of kinetic energy of all molecules present in substance. Unite of heat is joule (J) in SI unit. It is unit in CGS unit is calorie.
[1 calorie=4.2 joule]
Amount of Heat present in a boby is affected by;
i. Number of molecules present in body.
ii. Average Kinetic energy of molecules.
Temperature:
It is the degree of hotness or coldness of a substance Temperature is also defined as the average kinetic energy of the molecules of the body. Kelvin (K) is SI unit of temperature.
Some Effects of Heat:
i. Expansion of body
ii. Change of state of body
- Change in temperature of body
- Change in solubility of body
- Physical and chemical changes of body
Anomalous expansion of water:
Generally liquids expands on heating and contracts on cooling but when water is heated from 00C the volume decreases up to 40C and increases beyond 40C. This unusual expansion of water from 00C to 40C is known as anomalous expansion of water.
Scientific fact of Anomalous expansion of water:
Anomalous expansion of water takes place because when water is heated up to 4oC hydrogen bonds are formed. Thoughts ice is supposed to expand when it is converted into water, this gradual formation of hydrogen bond causes it to contract, i.e. the contraction caused due to the formation of hydrogen bond is greater than the actual expansion of ice. At 4oC water has maximum density because all the hydrogen bonds are formed by 4oC beyond which water obeys kinetic theory of molecules, an increase in volume when heated and the reverse when cooled, the same thing happens in reverse when water is called beyond 4oC.
Advantages of anomalous expansion of water
- Existence of marine life in cold countries even in winter.
- Drinks are stored inside the pond to prevent freezing in the cold countries.
Disadvantages of anomalous expansion of water.
- Water pipes burst due to expansion of water in colder regions.
Heat Equation:
Let object of mass (m) is heated from ‘t1’ temperature to ‘t2’ by supplying ‘Q’ amount of heat. Let ‘dt’ is change in temperature. Then it is found that;
Heat gained to body is directly proportional to mass
i.e.Qαm- – – – (i)
Also heat gained by body is directly proportional to change in temperature.
i.e. Qαdt —— (ii)
Combining (i) and (ii)
Qαmdt
Or [Q=msdt] where S is the specific heat capacity of body.
Specific heat capacity:
The amount of heat required to change the temperature of a substance of unit mass by 10C is known as specific heat capacity. Its SI unit is J/Kg0C.
Principle of calorimetry:
Amount of heat gained by cold body is equal to the amount of heat lost by hot body. i.e. [heat gained= Heat lost]
REASONABLE FACTS
1. If heat is supplied to a solid continuously, it melts.
Ans- When solid is heated, the Kinetic energy of the molecules increases which decrease the binding force of molecules and hence the intermolecular distance increases as a result if heat is supplied to a solid continuously, it melts.
2. A thick glass tumbler crack when boiling water is poured in it.
Ans- Glass is a bad conductor of heat. So when boiling water is poured in a thick glass tumbler, the inner surface gets suddenly expanded whereas the outer surface remains same. Hence due to such unequal expansion of inner and outer surfaces, the thick glass tumbler cracks.
3. Sea breeze occurs at days and land breeze occurs at nights.
Ans- because water has maximum specific heat capacity and sand has less specific heat capacity.
Due to it, at days sand of land is heated faster than water and the air above it becomes less dense by its expansion. Thus, air above the seas being denser blow towards the land and sea breeze occurs. But at night the sea water cools slowly but sand cools faster. Now the air above sea water becomes less dense and that above land is denser. Thus, air over lands moves towards the sea and land breeze occurs.
4. A wet handkerchief is kept on the forehead of the patient suffering from fever.
Ans- When a person is suffering from fever, a handkerchief is kept on the forehead to lower his/her body temperature. As the wet handkerchief contains water, it can absorb a large amount of heat due to its high specific heat capacity. As a result, the temperature (i.e.high fever) reduces. Hence a wet handkerchief is kept on the forehead of the patient suffering from fever.
5. The metal antimony behaves like water.
Ans- The metal antimony expands on freezing and contracts at first when warmed above its melting point. Due to such expansion, it makes sharp castings. Hence it behaves like water.
6. Water is the earthen pot is cooler than that in a metal pot.
Ans- Earthen pot is porous. Due to capillary action, small amount of water of the pot rises to the outer surface of pot. The heat energy absorbed from environment evaporates water from the surface of the pot. The temperature of water in the pot doesn’t get heat from the environment and remains cold.
7. Vegetables and fruits get damaged during severe frost.
Ans- Vegetables, fruits and plants get damaged during severe frost when temperature falls below 4oC because water present in there things expends As a result, the cell walls of fruits may burst due to expansion of water inside them.
8. When we get out of bed in the very cold morning we feel air of the room cold but when we come back staying outside for some time, we felt air in the room warm.
Ans- Heat always flows from high temperature to low temperature. The temperature of our body is higher than that of air temperature of the room. So heat flows from our body to the air of room and we feel cold. But when we came back to the same room after staying outside for some time, our body temperature is lower than that of air temperature of the room. So heat flows from the air to our body and we feel warm.
9. The temperature of water at the bottom of a pond is 40Cwhen its surface water freezes.
Ans- The temperature of water at the bottom of pond is 40C when its surface water freezes due to the highest density, that cause water at 40Cdenser and sinks at the bottom.
10. Fish can survive under a pond where the surface is even covered with ice.
Ans- Water has maximum density at 40C.due to the anomalous expansion of water and is found at the bottom of the pond. There are other layers of water of 30C, 20C and 10C respectively above water of 00C. As ice is insulator of heat so it does not allow the heat of pond water to escape out. Hence, fish can survive under a pond where the surface is even covered with ice.
11. Soft drink bottles are not completely filled.
Ans- A bottle completely filled with water is cooled at 00Cin refrigerator, it expands due to anomalous expansion of water i.e. ice has large volume. The increase in volume gives very large force on the bottle and gets burst. So to prevent such bursting of the bottle they are not filled completely.
12. The water pipes filled with water often burst in water.
Ans- Water pipes burst in winter season due to anomalous expansion of water. When water is cooled from40C to 00C, the volume of water starts to increase due to which there will not be enough space for the increased volume of warer inside the pipe and gives outward pressure. Hence, the water pipes filled with water often burst in winter.
13. If a beaker completely filled with water of 40Cis heated or cooled, water overflows.
Ans- If a beaker completely filled with water of 40Cis heated or cooled, water overflows because of anomalous expansion of water as it has least volume at this temperature. When water at 40Cis heated or cooled its volume increases.
14. The deserts is very hot at day and very cold at night.
Ans- Sand gets heated quickly due to the sun’s heat during day time and gets cooler soon in the absence of sun’s heat at night due to less specific heat capacity of sand so the desert is very hot at day and very cold at night.
15. The climate nearby the oceans remains pleasant throughout the year.
Ans- The specific heat capacity of sand is five times lesser than that of water so the temperature of the land remains higher than that of water at day and heat flows from land to the ocean and occurs vice-versa at night. Hence, the climate nearby the oceans remains pleasant throughout the year.
16. If the sand and water of equal weight are heated, the temperature of sand will be higher.
Ans- If the sand and water of equal weight are heated, the temperature of sand will be higher because it has less specific heat capacity as sp. Heat capacity of substance is inversely proportional to the increasing temperature.
17. Milk boils faster than water.
Ans- Water has very high specific heat capacity (4200J/Kg0C) as compared with other liquids (e.g. oil, water etc) so it takes a longer time to boil as it takes larger amount of heat to boil.
18. Steel chair feel colder than the wooden chair during the winter season.
Ans- During winter season, when the temperature fall down the amount of heat lost by the steel chair will be greater than the wooden chair because the specific heat capacity of steel or iron is greater than the wood.
19. Equal mass of water and oil heated for some time, water cools slowly than oil.
Ans- Equal mass of water and oil heated for some time, when cools down water cools slowly than oil because water has very high specific heat capacity (4200J/Kg0C) as compared with other liquids (e.g. oil). So, it takes a long time to cool.
20. Ice is covered with saw dust prevents the ice to melt.
Ans- Since the saw dust is a poor conductor of heat and therefore it prevents the heat transfer from air to ice so ice is covered with saw dust prevents the ice to melt.
21. The water is used in the hot water bag instead of oil.
Ans- The water is used in the hot water bag instead of oil because water has very high specific heat capacity (4200J/Kg0C) as compared with other liquids (e.g. oil) and it can store a large amount of heat energy for a longer period of time in the water bag. So, the water is used in the hot water bag instead of oil.
22. Water is used in cooling the engines of motor car.
Ans- Water has capacity to absorb a large amount of heat from the heat engines as it has very high specific heat capacity Error! Not a valid link. as compared with other liquids. So, water is used in cooling the engines of motor car.
23. Well water is warmer in the morning during winter season.
Ans- The specific heat capacity of soil is very less as compared to that of water so during winter night, the temperature of soil decreases very fast than that of water. Hence, well water is warmer in the morning during winter season.
24. We wear warm clothes in winter.
Ans- During winter , the temperature of surrounding is very low as compared to our body temperature. So, more amount of heat is lost from our body to the surrounding and we feel very cold. Hence , we wear warm clothes in winter to prevent the heat loss from the body as the woolen clothes are also the bad conductor of heat.
25. A new quilt is felt warmer than an old one.
Ans- A new quilt encloses more spaces that get filled with more air as compared to that of the old quilt. Since, air is bad conductor of heat, it does not allow the heat to flow from the body to the surrounding. As a result, a new quilt is felt warmer than the old one.
26. During the winter, the animals curl into a ball.
Ans- The amount of heat loss by a baby depends upon its area. When the animals curt into a ball, the surface area of their body will be reduced. As a result, the heat loss to the surrounding will be reduced. This helps them to remain warm in the winter.
27. We sweat in summer.
Ans- In summer, the atmospheric temperature goes up higher than our normal body temperature (37C). To maintain our body temperature fixed at 37C, our body loses the excess heat by excreting sweat. So, we sweat in summer.
29. Water solidifies from top but ghee solidifies from bottom.
Ans- The density of solid form of water is less than its liquid form so, it floats and seems to be solidifying from top but the solid ghee has more density than its liquid form and sinks and seems to be solidifying from bottom.
29. The density of water is maximum at 40C.
Ans- The volume of water is minimum at 40C. So the density of water is maximum at that temperature- [ ∵d=m/v] i.e. density is inversely proportional to the volume.
30. Mercury is used as thermometric liquid.
Ans- Mercury is used as a thermometric liquid because
i) It is a good conductor of heat.
ii) It has low specific heat capacity, i.e. 140J/Kg0C
31. Alcoholic thermometer cannot measure the boiling point of water.
Ans- The boiling point of alcohol is less than that of water. (Boiling point of alcohol=780C and boiling point of water=1000C) so the boiling point of water cannot be measured by using alcoholic thermometer.
32. Heat always flows from a body from higher temperature to the body at lower temperature.
Ans- Average kinetic energy of molecules of hot body is more than that of cold body. When molecules with more K.E. are in contact with less energetic molecules they give up some of their K.E. to less energetic one. Therefore, the direction of flow of heat is from the hotter to the colder objects.
33. Different materials posses’ different specific heat.
Ans- Different materials absorb energy in different ways. The energy may increase the to and fro vibration motion of molecules, which raises the temperature, or it may increase the amount of internal vibration or rotation within the molecules and go into potential energy, which does not raise the temperature. General there is combination of both. For this reason, different materials possess different specific heat.
Heat:
Definition: The heat is a form of energy which produces the sensation of warmth (Hotness). It is measured in Joule(J).
Temperature:
Definition: The degree of hotness or coldness of a body is called temperature.Its SI unit is Kelvin (K).
A relation between Joule and Calorie:
2.4 Joule=1 calories
alorie: The amount of heat used to raise the temperature of a 1gm substance by 1°C is called Calorie.
A relationship among Celcius, Fahrenheit, and Kelvin:
C-0°/100 = F-32°/180 = K-273°/100
or, C-0°/10 = F-32°/18 = K-273°/10
Source of energy: The largest source of energy is called Sun. It radiates heat and light by nuclear.
A principle of Nuclear fusion: E=mc²
Specific heat capacity (S):
Definition: The amount of heat required to raise the temperature of a 1kg substance by 1°C is called Specific heat capacity (S).
Q∝m — (a)
Q∝ ΔE — (b)
From (a) and (b)
Q∝ Δt
or, Q=smΔt
Where,
Q= Amount of heat (Joule)
m= Mass of substance (Kg)
Δt= Difference in temperature (C°).
S= Specific heat capacity.
S= Q/mΔt
= Joule/Kg°C
=J/kg°C
Factors on which Specific heat capacity depends:
- S∝Q
- S∝1/m
- S∝1/Δt
Thermometer:
Name of thermometric liquid:
- Mercury (Freezing point = -39°c and boiling point= 357°c
- Alcohol (Freezing point = -117°c and boiling point= 78°c
Thermometer: It is used to measure temperature.
Types: a)Mercury or Clinical thermometer
b) Alcohol thermometer
c) Digital thermometer
d) Maximum and minimum thermometer, etc.
Mercury or Clinical thermometer: It is used by the doctor to measure the temperature of the human body. It is a mercury thermometer. The normal body temperature is 37°c (98.6°F).
Digital thermometer: It is used by the thermistor at one end. Its reading is more accurate than Mercury thermometer.
Alcohol thermometer: The freezing point of an alcohol thermometer is -117°c and boiling point is 78°c. So, it is suitable to measure the temperature of the very cold region.
Maximum and Minimum thermometer: It uses mercury and alcohol as the thermometric liquid. It is U-shape in construction and used to measure maximum and the minimum temperature of an environment.
Heat Equation:
Definition: According to this equation the heat lost by not body is equal to the heat gained by the cold body.
- Heat lost= Heat gained
m1S1(t1-t)= m2s2(t-t2) - It is also called Principle of calorie try
- Explanation:
Case-1
mass= m1
Specific heat capacity= s1
Temperature= t1°c
∴Heat lose= m1S1(t1-t)
Case-2
mass= m2
Specific heat capacity= s2
Temperature= t°c
∴Heat gained= m2s2(t-t2) - ∴ Heat lost= Heat gained
or, m1S1(t1-t)= m2s2(t-t2)
The specific heat capacity of water is maximum: (4200J/14°). So, the water is heated slowly and cooled slowly.
Example: a) water is used in automobile engine as a heat absorber due to high specific heat capacity. It slowly absorbs heat for a long time.
b) The hot water bottle is used in a hospital to release stomach pain because of the specific heat capacity of water is more and it slowly cools down.
c)The temperature fluctuation is low on the island because it is surrounded by water which specific heat capacity is high. So, it gains or loses heat very slowly.
The specific heat capacity of sand is low, so it is quickly heated and cooled:
Example: In the desert, the day is very hot and the night is very cold due to the low specific heat capacity of sand which is quickly heated in a day and quickly cooled in the night.
Answer these questions:
- What is heat? On which factors does the amount of heat depend?
Ans: The heat is a form of energy which produces a sensation of warmth (Hotness).
The amount of heat depends on the speed of a particle. - Mention the effect of heat.
Ans: The effect of heat is given below:
a) Change in temperature.
b) Change in physical states, etc. - What is the temperature? How it is measured?
Ans: The degree of hotness or coldness of a body is called Temperature.
It is measured by the thermometer. - Differentiate between heat and temperature.
Ans: The differentiate between heat and temperature are given below:HeatTemperatureIt is a form of energy which produces the sensation of warmth.It is the degree of hotness or coldness of an object.Its SI unit is Joule (J).Its SI unit is Kelvin (k).It is measured by a calorimeter.It is measured by a thermometer. - What is a thermometer? What are the parts of thermometer?
Ans: The thermometer is a device which is used to measure the temperature of an object.
The parts of the thermometer are given below:
a) Bulb
b) Mercury
c) Glass tube
d) Temperature
e) Capillary tube
f) Constriction, etc. - Define:
a) Specific heat capacity: The amount of heat required to raise the temperature of a 1kg substance by 1°C is called Specific heat capacity (S).
b) One Calorie heat: The amount of heat used to raise the temperature of a 1gm substance by 1°C is called Calorie.
c) Heat capacity: The amount of heat required to raise the temperature of an object through 1°c is called Heat capacity. - What do you mean by the fact that the specific heat capacity of water is 4200 J/kg° c?
Ans: Specific heat capacity of water is 4200 J/kg°c because it slowly absorbs heat for a long time and releases heat after a long time. - Mention some effect of the highest specific heat capacity.
Ans: Some effect of highest specific heat capacity are given below:
a) Aquatic life will be in hazards due to high heating and freezing point.
b) Water will impure.
c) Global warming, etc. - What is the heat equation?
Ans: The amount of heat lost or gained by an object is equal to the product of mass, specific heat capacity and change in temperature are called the Heat Equation.
Give reasons:
- Water is used to cool the engines of vehicles.
Ans: Water is used to cool the engines of vehicles because it can absorb a large amount of heat from the hot engine without raising the temperature by a significant value. - A thick glass tumbler cracks when hot water is poured into it.
Ans: A thick glass tumbler cracks when hot water is poured into it because when hot water is poured into the glass, it can’t absorb hot water and got cracked. - Honey solidifies from the bottom whereas water solidifies from the top.
Ans: Honey solidifies from the bottom whereas water solidifies from the top because water’s density decreases and volume increases and it solidifies from the top but honey’s density decrease and its volume decrease. - It is very hot during the day and very cold at night.
Ans: It is very hot during the day and very cold at night because during day sand gets heated due to sun rapidly but during night sand losses heat rapidly and gets cool faster. - Temperature of coastal region remains fairly constant.
Ans: Temperature of the coastal region remains fairly constant due to the high specific heat capacity of water (4200 J/kg°c). The water plays a vital role in temperature fluctuation.
Numerical problems:
a) How much heat is required to increase the temperature of 5kg of water from 20°c to 70°c? (Given specific heat capacity of water= 4200 J/kg°c)
Given data,
m= 5kg
s= 4200 J/kg°c
t= 70°-20°c = 50°c
we know that,
H= s×m×t
= 4200×5×50
= 105×104 Joule
= 1.05×106 Joule
∴So, 1.05×106 Joule heat is required to increase the temperature of 5kg of water from 20°c to 70°c.
b) Calculate the final temperature of a pressure cooker of mass 1.5kg and temperature 30°c, when it is heated with 7.5×104 Joule. (The specific heat capacity of aluminum is 1000 J/kg°c)
Given data,
H= 7.5×104 Joule
s= 1000 J/kg°c
m= 1.5kg
t= t2-t1
=t2-30
we know that,
H= m×s×t
or, t= H/m×s
or, t2-30 = 7.5×104/1.5×1000 = 5×10/1
or, t2= 5×10+30
∴t2= 80°c∴So, the final temperature is 80°c.
c) The temperature of 20kg water in the radiator of an engine of a car is 30°c. It the temperature of the water increases to 100°c after the engine is heated. What quantity of heat is absorbed by the water?
Given data,
Mass(m)= 20kg
initial temperature (t1)= 30°c
Final temperature (t2)= 100°c
Change in temperature (dt)= t2-t1= 100°-30°= 70°c
Specific heat capacity (s)= 4200 J/kg°c
Amount of heat gained (Q)= ?
we know that,
Q= m.s.d.t
= 20×4200×70°
= 5880000
=5.88×106 Joule
∴The amount of heat gained is 5.88×106 Joule.
d) What will be the quantity of heat required to raise the temperature of 2kg paraffin by 10°c if 44000 Joule of heat energy is required to raise the temperature of the paraffin by 20°c?
Given data,
Mass (m)= 2kg
Specific heat capacity (s)=?
we have,
H=s.m.t
or, 44000= s×2×20
or, s= 44000/20×2
∴ s= 1100Now,
Q=m.s.t
=2×1100×10
=2.2×104 Joule
∴ The quantity of heat required to raise the temperature is 2.2×104 Joule
e) Hot water of 100°c is added to 300g of water at 0°c and the final temperature of the mixture reached 40°c. Find the mass of hot water added. (Given, the specific heat capacity of water= 4200° J/kg°c)
Given data,
Condition- i
t1= 100°c
m1=?
S1= 4200 kg°c
Condtion- ii
t2= 100°c
m2=?
S2= 4200 kg°c
∴t= 40°c
we know that,
m1s1(t1-t)= m2s2 (t-t2)
or, m1= m2s2 (t-t2)/s1(t1-t)
or, m1= 0.3×40/60= 1.2/6= 0.2kg
∴Required amount of hot water is 0.2 kg.
f)The temperature of the water is 5°c in the winter season. If 20 liters of water is to be heated to 35°c for taking a bath. Calculate the amount of heat required for it.
Given data,
s= 4200 J/kg
Mass (m)= 20kg
temperature (t)= 30°c
we know that,
H= s.m.t
=4200×20×30
= 2.52 ×106
∴The amount of heat required for it is 2.52 ×106
g) For taking a bath, water at 40°c is required. Calculate the mass of water at 15°c to be added to 80kg water at 80°c for making it suitable for bathing.
Given data,
t= 40°c
t1= 15°c
m2= 80kg
t2= 80°c
s= 4200 j/kg
m1=?
we know that,
m1s1 (t1-t)= m2s2 (t-t2)
or, m1= m2s2 (t-t2)/s1 (t1-t)
or, m1= 80×(40-80)/ 15-40
or, m1= 80× (–40)/–20
or, m1= 3200/ 25
or, m1= 128kg
∴ Mass of water is 128 kg.
