Heat
$\displaystyle \small \bullet$ Heat is a form of energy which makes us feel hot or cold
$\displaystyle \small \bullet$ Heat is the kinetic energy of the molecules in motion
$\displaystyle \small \bullet$ Units of heat
$\displaystyle \small \circ$ Calorie: The amount of heat required to raise the temperature of 1 gm of water through 1$\displaystyle \small ^{0}C$.
$\displaystyle \small \circ$ Centigrade Heat Unit (C.H.U.): The amount of heat required to raise the temperature of 1 lb of water through 1$\displaystyle \small ^{0}C$.
$\displaystyle \small \circ$ British Thermal Unit (B.T.U.): The amount of heat required to raise the temperature of 1 lb of water through 1$\displaystyle \small ^{0}F$.
$\displaystyle \small \circ$ Joule: S.I. Unit (1 Calorie = 4.186 joule)
Specific Heat
$\displaystyle \small \bullet$ The quantity of heat required to raise the temperature of one gram of substance through 1$\displaystyle \small ^{0}C$ is called specific heat.
$\displaystyle \small \bullet$ It is denoted by ‘s’
$\displaystyle \small \bullet$ Unit of specific heat: J/KgK, Cal/g$\displaystyle \small ^{0}C$.
Thermal Capacity
$\displaystyle \small \bullet$ Thermal capacity of a substance is the amount of heat required to raise the temperature of a substance through 1$\displaystyle \small ^{0}C$.
$\displaystyle \small \bullet$ Thermal capacity of substance, Q = ms calories/$\displaystyle \small ^{0}C$.
Calorific value
The amount of heat released by the complete combustion of unit quantity of the fuel (mass or volume) is known as calorific value of fuels.
Water Equivalent of Heat
$\displaystyle \small \bullet$ It is the amount of water which requires the same amount of heat as required to heat the substance to 1$\displaystyle \small ^{0}C$.
$\displaystyle \small \bullet$ Water equivalent, W = ms gm.
Types of Heat
Sensible Heat
Sensible heat is the heat absorbed or given off by a substance without changing its physical state
Latent Heat
The heat gained or given by the substance during a change of state (from solid to liquid to gas) is called latent heat or hidden heat.
Latent heat of fusion
$\displaystyle \small \bullet$ The amount of heat required per unit mass of a substance at melting point to convert it from the solid to the liquid state is called latent heat of fusion of solid. Its unit is cal/gram.
$\displaystyle \small \bullet$ Latent heat of fusion of ice (L) = 80 cal/gram
Latent heat of vaporisation
$\displaystyle \small \bullet$ The amount of heat required to vaporise a unit mass of liquid at its boiling point is called latent heat of vapourisation.
$\displaystyle \small \bullet$ Latent heat of steam(L) = 540 cal/gram
Temperature
$\displaystyle \small \bullet$ The degree of hotness of a body, compared with some standard is called temperature of the body
$\displaystyle \small \bullet$ Units of temperature: Kelvin (K), Degree Centigrade ($\displaystyle \small ^{0}C$), Degree Fahrenheit ($\displaystyle \small ^{0}F$)
Boiling Point
Any substance starts turning into a gas shows the temperature at which it boils this is known as the boiling point. The boiling point of water is 100$\displaystyle \small ^{0}C$.
Melting Point
The temperature at which any solid melts into liquid or liquid freezing to solid is called the melting point of substance. The melting point of ice is 0$\displaystyle \small ^{0}C$.
Temperature Scales
$\displaystyle \small \frac{C}{100}=\frac{F-32}{180}=\frac{Re}{80}$
$\displaystyle \small \frac{C}{5}=\frac{F-32}{9}=\frac{Re}{4}$
Measuring Heat Energy
Calorimeter
$\displaystyle \small \bullet$ The apparatus used to measure the amount of heat by mixer method is called calorimeter. It is nothing but cylindrical shaped vessel and a stirrer made out of mostly copper.
$\displaystyle \small \bullet$ In a calorimeter when the hotter solid/liquid substance are mixed with the cooler solid/liquid substances, heat transfer takes place until both substances reach the same temperature. By the same time calorimeter also reaches the same temperature.
Quantity of Heat
$\displaystyle \small \bullet$ The quantity of heat gained or lost by a body depends on the mass, specific heat and temperature of the substance.
$\displaystyle \small \bullet$ Quantity of heat in the substance $\displaystyle \small =m\times s\times \Delta t$
where,
m = mass of substance
s = specific heat
$\displaystyle \small \Delta t$ = rise in temperature
Interchange of Heat
$\displaystyle \small \bullet$ Heat flows from higher temperature to lower temperature.
$\displaystyle \small \bullet$ If a solid is heated and dipped in cold water then, heat is transferred from solid to water.
$\displaystyle \small \bullet$ The solid loses heat and water gains heat till the temperature of solid and water becomes equal.
$\displaystyle \small \bullet$ Heat lost = Heat gained
$\displaystyle \small m_{1}s_{1}t_{1}=m_{2}s_{2}t_{2}$
where,
$\displaystyle \small m_{1}$ = mass of solid
$\displaystyle \small s_{1}$ = specific heat of solid
$\displaystyle \small t_{1}$ = temperature of solid
$\displaystyle \small m_{2}$ = mass of water
$\displaystyle \small s_{2}$ = specific heat of water
$\displaystyle \small t_{2}$ = temperature of water
Transmission of Heat
$\displaystyle \small \bullet$ Heat can be transmitted from one body to another
$\displaystyle \small \bullet$ Methods of heat transmission
$\displaystyle \small \circ$ Conduction: It is the flow of heat from the hotter to the colder region of a body without any visible movement of the particles of the body. Ex: heating iron rod
$\displaystyle \small \circ$ Convection: In this method heat gets transferred by the motion of heated particles. On heating water it takes heat and comes upwards while cold water from top goes to the bottom. Ex: boiling water
$\displaystyle \small \circ$ Radiation: In this system, heat does not need any medium. The heat goes direct from source in the form of rays to the point of consumption. Ex: sun rays reaching ground
Temperature Measuring Instruments
Thermometer
$\displaystyle \small \bullet$ Thermometers are based on the principle that liquid and solids expand, when they are subjected to heat.
$\displaystyle \small \bullet$ A common thermometer consists of a capillary glass tube filled with mercury having both of its ends sealed.
$\displaystyle \small \bullet$ It has a bulb at one end to store mercury at low temperatures.
$\displaystyle \small \bullet$ As the bulb is kept in contact with hot body, mercury is heated and it expands along the capillary tube.
$\displaystyle \small \bullet$ On cooling the bulb, mercury thread contracts.
$\displaystyle \small \bullet$ Can measure upto 300$\displaystyle \small ^{0}C$.
$\displaystyle \small \bullet$ Advantages of Mercury
$\displaystyle \small \circ$ It expands almost uniformly with rise in temperature
$\displaystyle \small \circ$ It can be easily seen in the tube
$\displaystyle \small \circ$ It does not wet the surface of the tube
$\displaystyle \small \circ$ It is a good conductor of heat
$\displaystyle \small \circ$ It is easily available in pure state
$\displaystyle \small \bullet$ Disadvantages of Mercury
$\displaystyle \small \circ$ Its freezing point is low (-39$\displaystyle \small ^{0}C$)
$\displaystyle \small \circ$ Its boiling point is high (357$\displaystyle \small ^{0}C$)
$\displaystyle \small \circ$ So it remains as liquid over a large range of temperature
Thermo-couple
$\displaystyle \small \bullet$ It is an arrangement where circuit is closed by wires of different metals.
$\displaystyle \small \bullet$ One wire is kept at low temperature and other at high temperature.
$\displaystyle \small \bullet$ Thermos-electro-motive force is created which can be seen by galvanometer.
$\displaystyle \small \bullet$ This works on the effect of seebeck.
$\displaystyle \small \bullet$ Thermocouple elements:
$\displaystyle \small \circ$ Nickel – Iron (300$\displaystyle \small ^{0}C$ to 600$\displaystyle \small ^{0}C$)
$\displaystyle \small \circ$ Iridium – Platinum (0$\displaystyle \small ^{0}C$ to 1600$\displaystyle \small ^{0}C$)
$\displaystyle \small \circ$ Copper – Constantan (0$\displaystyle \small ^{0}C$ to 1880$\displaystyle \small ^{0}C$)
Pyrometer
$\displaystyle \small \bullet$ Pyrometer is used to measure temperature of furnaces and other high temperatures.
$\displaystyle \small \bullet$ This works on the law of thermocouple.
$\displaystyle \small \bullet$ Types of pyrometer
(i) Thermo-Electric Pyrometer
(ii) Optical Pyrometer
Thermo-Electric Pyrometer
$\displaystyle \small \bullet$ The hot end is welded and closed in porcelain or silicon pipe which is placed in furnace and cold end is kept in water.
$\displaystyle \small \bullet$ e.m.f. produced can be read in galvanometer.
$\displaystyle \small \bullet$ Can measure temperature upto 2000$\displaystyle \small ^{0}C$
$\displaystyle \small \bullet$ It is simple and durable.
Optical Pyrometer/ Radiation Pyrometer
$\displaystyle \small \bullet$ This instrument concentrates on thermal rays through an optical lens and focus them on to a thermo element.
$\displaystyle \small \bullet$ Optical pyrometer use the variation of colour with variation of its temperature.
$\displaystyle \small \bullet$ The colour of hot body turns from red to white as its temperature increases.
$\displaystyle \small \bullet$ This colour is matched with the colour of a glowing filament carrying electric current.
$\displaystyle \small \bullet$ Thus, by measuring currents passing through the filament, the temperature of the hot body is estimated.
$\displaystyle \small \bullet$ Can measure temperature upto 3000$\displaystyle \small ^{0}C$
Expansion of Solids
$\displaystyle \small \bullet$ All materials expand on heating and contract on cooling.
$\displaystyle \small \bullet$ Types of Expansion
1. Linear expansion: expansion in length is termed as linear expansion.
Coefficient of linear expansion is defined as the increase in length per degree rise in temperature.
$\displaystyle \small \alpha =\frac{l_{2}-l_{1}}{l_{1}(t_{2}-t_{1})}$
where,
$\displaystyle \small \alpha$ = coefficient of linear expansion
$\displaystyle \small l_{1}$ = initial length
$\displaystyle \small l_{2}$ = final length
$\displaystyle \small t_{1}$ = initial temperature
$\displaystyle \small t_{2}$ = final temperature
2. Superficial expansion: expansion in area is termed as superficial expansion.
Coefficient of superficial expansion is defined as the increase in area per degree rise in temperature.
$\displaystyle \small \beta =2\alpha$
3. Cubical expansion: expansion in volume is termed as cubical expansion.
Coefficient of cubical expansion is defined as the increase in volume per degree rise in temperature.
$\displaystyle \small \gamma =3\alpha$
Insulating Materials
$\displaystyle \small \bullet$ The material which restrict heat flow is called insulating materials.
$\displaystyle \small \bullet$ Properties: Low conductivity, Resistance to fire, Less moisture absorption, Good rigidity, Odourless, Vapour permeability, Light in weight.
$\displaystyle \small \bullet$ Insulating Materials: Thermocole, Fibreglass, Glass wool, Puf
Pressure
Pressure is an expression of force exerted on a surface per unit area.
SI unit: Pascal (Pa)
Metric unit: Bar
$\displaystyle \small 1 Pascal=1 N/m^{2}$
$\displaystyle \small 1 Bar=10^{5} Pascal$
$\displaystyle \small \bullet$ Heat is a form of energy which makes us feel hot or cold
$\displaystyle \small \bullet$ Heat is the kinetic energy of the molecules in motion
$\displaystyle \small \bullet$ Units of heat
$\displaystyle \small \circ$ Calorie: The amount of heat required to raise the temperature of 1 gm of water through 1$\displaystyle \small ^{0}C$.
$\displaystyle \small \circ$ Centigrade Heat Unit (C.H.U.): The amount of heat required to raise the temperature of 1 lb of water through 1$\displaystyle \small ^{0}C$.
$\displaystyle \small \circ$ British Thermal Unit (B.T.U.): The amount of heat required to raise the temperature of 1 lb of water through 1$\displaystyle \small ^{0}F$.
$\displaystyle \small \circ$ Joule: S.I. Unit (1 Calorie = 4.186 joule)
Specific Heat
$\displaystyle \small \bullet$ The quantity of heat required to raise the temperature of one gram of substance through 1$\displaystyle \small ^{0}C$ is called specific heat.
$\displaystyle \small \bullet$ It is denoted by ‘s’
$\displaystyle \small \bullet$ Unit of specific heat: J/KgK, Cal/g$\displaystyle \small ^{0}C$.
Thermal Capacity
$\displaystyle \small \bullet$ Thermal capacity of a substance is the amount of heat required to raise the temperature of a substance through 1$\displaystyle \small ^{0}C$.
$\displaystyle \small \bullet$ Thermal capacity of substance, Q = ms calories/$\displaystyle \small ^{0}C$.
Calorific value
The amount of heat released by the complete combustion of unit quantity of the fuel (mass or volume) is known as calorific value of fuels.
Water Equivalent of Heat
$\displaystyle \small \bullet$ It is the amount of water which requires the same amount of heat as required to heat the substance to 1$\displaystyle \small ^{0}C$.
$\displaystyle \small \bullet$ Water equivalent, W = ms gm.
Types of Heat
Sensible Heat
Sensible heat is the heat absorbed or given off by a substance without changing its physical state
Latent Heat
The heat gained or given by the substance during a change of state (from solid to liquid to gas) is called latent heat or hidden heat.
Latent heat of fusion
$\displaystyle \small \bullet$ The amount of heat required per unit mass of a substance at melting point to convert it from the solid to the liquid state is called latent heat of fusion of solid. Its unit is cal/gram.
$\displaystyle \small \bullet$ Latent heat of fusion of ice (L) = 80 cal/gram
Latent heat of vaporisation
$\displaystyle \small \bullet$ The amount of heat required to vaporise a unit mass of liquid at its boiling point is called latent heat of vapourisation.
$\displaystyle \small \bullet$ Latent heat of steam(L) = 540 cal/gram
Temperature
$\displaystyle \small \bullet$ The degree of hotness of a body, compared with some standard is called temperature of the body
$\displaystyle \small \bullet$ Units of temperature: Kelvin (K), Degree Centigrade ($\displaystyle \small ^{0}C$), Degree Fahrenheit ($\displaystyle \small ^{0}F$)
Boiling Point
Any substance starts turning into a gas shows the temperature at which it boils this is known as the boiling point. The boiling point of water is 100$\displaystyle \small ^{0}C$.
Melting Point
The temperature at which any solid melts into liquid or liquid freezing to solid is called the melting point of substance. The melting point of ice is 0$\displaystyle \small ^{0}C$.
Temperature Scales
$\displaystyle \small \frac{C}{100}=\frac{F-32}{180}=\frac{Re}{80}$
$\displaystyle \small \frac{C}{5}=\frac{F-32}{9}=\frac{Re}{4}$
| Scale | Freezing Point | Boiling Point |
|---|---|---|
| Centigrade | $\displaystyle \small ^{0}C$ | 100$\displaystyle \small ^{0}C$ |
| Fahrenheit | 32$\displaystyle \small ^{0}F$ | 212$\displaystyle \small ^{0}F$ |
| Kelvin | 273K | 373K |
| Reaumur | 0$\displaystyle \small ^{0}Re$ | 80$\displaystyle \small ^{0}Re$ |
Measuring Heat Energy
Calorimeter
$\displaystyle \small \bullet$ The apparatus used to measure the amount of heat by mixer method is called calorimeter. It is nothing but cylindrical shaped vessel and a stirrer made out of mostly copper.
$\displaystyle \small \bullet$ In a calorimeter when the hotter solid/liquid substance are mixed with the cooler solid/liquid substances, heat transfer takes place until both substances reach the same temperature. By the same time calorimeter also reaches the same temperature.
Quantity of Heat
$\displaystyle \small \bullet$ The quantity of heat gained or lost by a body depends on the mass, specific heat and temperature of the substance.
$\displaystyle \small \bullet$ Quantity of heat in the substance $\displaystyle \small =m\times s\times \Delta t$
where,
m = mass of substance
s = specific heat
$\displaystyle \small \Delta t$ = rise in temperature
Interchange of Heat
$\displaystyle \small \bullet$ Heat flows from higher temperature to lower temperature.
$\displaystyle \small \bullet$ If a solid is heated and dipped in cold water then, heat is transferred from solid to water.
$\displaystyle \small \bullet$ The solid loses heat and water gains heat till the temperature of solid and water becomes equal.
$\displaystyle \small \bullet$ Heat lost = Heat gained
$\displaystyle \small m_{1}s_{1}t_{1}=m_{2}s_{2}t_{2}$
where,
$\displaystyle \small m_{1}$ = mass of solid
$\displaystyle \small s_{1}$ = specific heat of solid
$\displaystyle \small t_{1}$ = temperature of solid
$\displaystyle \small m_{2}$ = mass of water
$\displaystyle \small s_{2}$ = specific heat of water
$\displaystyle \small t_{2}$ = temperature of water
Transmission of Heat
$\displaystyle \small \bullet$ Heat can be transmitted from one body to another
$\displaystyle \small \bullet$ Methods of heat transmission
$\displaystyle \small \circ$ Conduction: It is the flow of heat from the hotter to the colder region of a body without any visible movement of the particles of the body. Ex: heating iron rod
$\displaystyle \small \circ$ Convection: In this method heat gets transferred by the motion of heated particles. On heating water it takes heat and comes upwards while cold water from top goes to the bottom. Ex: boiling water
$\displaystyle \small \circ$ Radiation: In this system, heat does not need any medium. The heat goes direct from source in the form of rays to the point of consumption. Ex: sun rays reaching ground
Temperature Measuring InstrumentsThermometer
$\displaystyle \small \bullet$ Thermometers are based on the principle that liquid and solids expand, when they are subjected to heat.
$\displaystyle \small \bullet$ A common thermometer consists of a capillary glass tube filled with mercury having both of its ends sealed.
$\displaystyle \small \bullet$ It has a bulb at one end to store mercury at low temperatures.
$\displaystyle \small \bullet$ As the bulb is kept in contact with hot body, mercury is heated and it expands along the capillary tube.
$\displaystyle \small \bullet$ On cooling the bulb, mercury thread contracts.
$\displaystyle \small \bullet$ Can measure upto 300$\displaystyle \small ^{0}C$.
$\displaystyle \small \bullet$ Advantages of Mercury$\displaystyle \small \circ$ It expands almost uniformly with rise in temperature
$\displaystyle \small \circ$ It can be easily seen in the tube
$\displaystyle \small \circ$ It does not wet the surface of the tube
$\displaystyle \small \circ$ It is a good conductor of heat
$\displaystyle \small \circ$ It is easily available in pure state
$\displaystyle \small \bullet$ Disadvantages of Mercury
$\displaystyle \small \circ$ Its freezing point is low (-39$\displaystyle \small ^{0}C$)
$\displaystyle \small \circ$ Its boiling point is high (357$\displaystyle \small ^{0}C$)
$\displaystyle \small \circ$ So it remains as liquid over a large range of temperature
Thermo-couple
$\displaystyle \small \bullet$ It is an arrangement where circuit is closed by wires of different metals.
$\displaystyle \small \bullet$ One wire is kept at low temperature and other at high temperature.
$\displaystyle \small \bullet$ Thermos-electro-motive force is created which can be seen by galvanometer.
$\displaystyle \small \bullet$ This works on the effect of seebeck.
$\displaystyle \small \bullet$ Thermocouple elements: $\displaystyle \small \circ$ Nickel – Iron (300$\displaystyle \small ^{0}C$ to 600$\displaystyle \small ^{0}C$)
$\displaystyle \small \circ$ Iridium – Platinum (0$\displaystyle \small ^{0}C$ to 1600$\displaystyle \small ^{0}C$)
$\displaystyle \small \circ$ Copper – Constantan (0$\displaystyle \small ^{0}C$ to 1880$\displaystyle \small ^{0}C$)
Pyrometer
$\displaystyle \small \bullet$ Pyrometer is used to measure temperature of furnaces and other high temperatures.
$\displaystyle \small \bullet$ This works on the law of thermocouple.
$\displaystyle \small \bullet$ Types of pyrometer
(i) Thermo-Electric Pyrometer
(ii) Optical Pyrometer
Thermo-Electric Pyrometer
$\displaystyle \small \bullet$ The hot end is welded and closed in porcelain or silicon pipe which is placed in furnace and cold end is kept in water.
$\displaystyle \small \bullet$ e.m.f. produced can be read in galvanometer.
$\displaystyle \small \bullet$ Can measure temperature upto 2000$\displaystyle \small ^{0}C$
$\displaystyle \small \bullet$ It is simple and durable.
Optical Pyrometer/ Radiation Pyrometer
$\displaystyle \small \bullet$ This instrument concentrates on thermal rays through an optical lens and focus them on to a thermo element.
$\displaystyle \small \bullet$ Optical pyrometer use the variation of colour with variation of its temperature.
$\displaystyle \small \bullet$ The colour of hot body turns from red to white as its temperature increases.
$\displaystyle \small \bullet$ This colour is matched with the colour of a glowing filament carrying electric current.
$\displaystyle \small \bullet$ Thus, by measuring currents passing through the filament, the temperature of the hot body is estimated.
$\displaystyle \small \bullet$ Can measure temperature upto 3000$\displaystyle \small ^{0}C$
Expansion of Solids$\displaystyle \small \bullet$ All materials expand on heating and contract on cooling.
$\displaystyle \small \bullet$ Types of Expansion
1. Linear expansion: expansion in length is termed as linear expansion.
Coefficient of linear expansion is defined as the increase in length per degree rise in temperature.
$\displaystyle \small \alpha =\frac{l_{2}-l_{1}}{l_{1}(t_{2}-t_{1})}$
where,
$\displaystyle \small \alpha$ = coefficient of linear expansion
$\displaystyle \small l_{1}$ = initial length
$\displaystyle \small l_{2}$ = final length
$\displaystyle \small t_{1}$ = initial temperature
$\displaystyle \small t_{2}$ = final temperature
2. Superficial expansion: expansion in area is termed as superficial expansion.
Coefficient of superficial expansion is defined as the increase in area per degree rise in temperature.
$\displaystyle \small \beta =2\alpha$
3. Cubical expansion: expansion in volume is termed as cubical expansion.
Coefficient of cubical expansion is defined as the increase in volume per degree rise in temperature.
$\displaystyle \small \gamma =3\alpha$
Insulating Materials
$\displaystyle \small \bullet$ The material which restrict heat flow is called insulating materials.
$\displaystyle \small \bullet$ Properties: Low conductivity, Resistance to fire, Less moisture absorption, Good rigidity, Odourless, Vapour permeability, Light in weight.
$\displaystyle \small \bullet$ Insulating Materials: Thermocole, Fibreglass, Glass wool, Puf
Pressure
Pressure is an expression of force exerted on a surface per unit area.
SI unit: Pascal (Pa)
Metric unit: Bar
$\displaystyle \small 1 Pascal=1 N/m^{2}$
$\displaystyle \small 1 Bar=10^{5} Pascal$
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