Heat and Temperature – Complete Study Notes

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👉🏻Heat and Temperature – TNPSC Physics Test Series

Introduction to Heat and Temperature

Heat and temperature are important concepts in science and are closely connected with many events we observe in our daily lives. Cooking food, boiling water, melting ice, drying clothes and feeling the warmth received from the Sun are some familiar examples related to thermal effects. A clear understanding of these basic concepts helps in studying several other areas of science.

In this Heat and Temperature study section, we will cover the fundamental ideas related to heat and temperature, their measurement, temperature scales, thermometers and the effects of heat. The section also explains important concepts such as heat transfer, conduction, convection, radiation, specific heat capacity, latent heat, change of state, thermal expansion and calorimetry.

For TNPSC aspirants, these concepts are useful for understanding questions based on basic science, everyday applications and fundamental principles of heat. The notes are organised topic-wise so that each concept can be studied separately and revised easily.

What is Heat?

Heat is a form of energy that is transferred from a body at a higher temperature to a body at a lower temperature due to the difference in temperature. Heat always flows naturally from a hotter body to a colder body until both bodies reach the same temperature. For example, when a hot cup of tea is kept in a room, heat flows from the tea to the surrounding air, causing the tea to cool.

The amount of heat required to heat a substance depends on several factors.

• The mass of the substance is important. For example, heating 2 litres of water requires more heat than heating 1 litre of water to the same temperature because there is more water to heat.
• The nature of the substance also matters. For example, a given amount of heat can raise the temperature of sand more quickly than water because different substances require different amounts of heat for the same temperature increase.
• The change in temperature is another factor. For example, heating water from 20°C to 40°C requires less heat than heating the same amount of water from 20°C to 80°C, because the second case involves a greater rise in temperature.

The SI unit of heat is the joule (J) because heat is a form of energy. The older unit calorie (cal) is also used in some contexts. One calorie is approximately equal to 4.186 joules.

Heat can be transferred in three main ways: conduction, convection and radiation. These methods explain how heat moves through solids, liquids, gases and even through empty space.

For TNPSC preparation, remember that heat and temperature are different concepts. Heat refers to energy transferred because of a temperature difference, whereas temperature indicates the thermal condition or degree of hotness or coldness of a body.

What is Temperature?

Temperature is a physical quantity that tells us the degree of hotness or coldness of a body. It helps us compare the thermal condition of different objects. For example, a glass of ice water has a lower temperature than water kept in a vessel exposed to sunlight.

Temperature is related to the motion of the particles present in a substance. The particles of matter are always in motion. When their average kinetic energy increases, the temperature of the substance increases. When their average kinetic energy decreases, the temperature decreases.

How Temperature Changes

• When a substance is heated, its particles generally gain energy and move more rapidly.
• When a substance is cooled, its particles generally lose energy and their average motion decreases.
• A higher temperature generally indicates greater average kinetic energy of the particles.
• Temperature difference determines the direction of heat transfer.
• Heat naturally flows from a body at higher temperature to a body at lower temperature.

Example : Consider a metal spoon kept in a bowl of hot soup. Initially, the soup has a higher temperature than the spoon. As they remain in contact, heat flows from the hot soup to the cooler spoon. The spoon becomes warmer because its temperature increases.

Remember: Temperature tells us the thermal condition of a body, whereas heat is energy transferred because of a temperature difference.

Difference Between Heat and Temperature

Heat and temperature are closely related, but they are not the same physical quantity. Heat refers to the energy transferred between bodies because of a difference in temperature, whereas temperature indicates the degree of hotness or coldness of a body. Understanding the difference between them is important for TNPSC examinations.

For example, when a metal spoon is placed in hot water, the spoon becomes warm because heat is transferred from the hotter water to the cooler spoon. The temperature of the water is initially higher than that of the spoon. As heat is transferred, the temperature of the spoon increases and the temperature difference gradually decreases. This shows that temperature determines the direction of heat transfer, while heat is the energy transferred from the hotter body to the colder body.

A simple way to remember the difference is: temperature tells us how hot or cold something is, while heat is energy transferred because of a temperature difference.

Measurement of Temperature

Temperature tells us how hot or cold a substance or object is. It cannot be measured accurately by simply touching an object, so a suitable instrument called a thermometer is used. A thermometer gives a numerical value of temperature according to a particular temperature scale.

The measurement of temperature is based on a physical property of a substance that changes in a predictable way when its temperature changes. For example, in a traditional liquid thermometer, the liquid expands when heated and contracts when cooled. The change in the level of the liquid is then used to determine the temperature.

How Temperature is Measured

• Temperature is measured using a thermometer.
• A thermometer contains a temperature-sensitive substance or sensor.
• The sensor responds to changes in temperature.
• The thermometer is calibrated using a suitable temperature scale.
• The temperature is then read from the scale or displayed by the instrument.
• Common temperature scales include Celsius, Fahrenheit and Kelvin.

Example

When a thermometer is placed in warm water, its temperature-sensitive material responds to the heat from the water. After the thermometer reaches the temperature of the water, its reading gives the temperature of the water.

Different thermometers are designed for different purposes. A clinical thermometer is used to measure human body temperature, while a laboratory thermometer is used to measure the temperature of substances during scientific experiments. Other types of thermometers are used for weather observations, industrial processes and other applications.

Temperature Scales

Temperature scales are systems used to express the temperature of a substance or object using numerical values. The commonly used temperature scales are Celsius, Fahrenheit and Kelvin. Each scale has its own reference points and divisions.

1. Celsius Scale

The Celsius scale is widely used for measuring temperature in everyday life.

• Freezing point of water: 0°C
• Boiling point of water: 100°C
• The interval between these two points is divided into 100 equal parts.
• Each division represents 1°C.

These values are applicable at standard atmospheric pressure.

2. Fahrenheit Scale

The Fahrenheit scale is another temperature scale used in some countries.

• Freezing point of water: 32°F
• Boiling point of water: 212°F
• The interval between these two points is divided into 180 equal parts.

These values are applicable at standard atmospheric pressure.

3. Kelvin Scale

The Kelvin scale is the SI temperature scale and is widely used in scientific measurements.

• Freezing point of water: approximately 273.15 K
• Boiling point of water: approximately 373.15 K
• Absolute zero: 0 K
• Absolute zero is equal to −273.15°C.
• Kelvin is written as K, without the degree symbol.

Important Temperature Conversions

Celsius to Kelvin:

K = °C + 273.15

Example:
25°C = 25 + 273.15 = 298.15 K

Celsius to Fahrenheit:

°F = (9/5 × °C) + 32

Example:
20°C = (9/5 × 20) + 32 = 68°F

Thermometers

A thermometer is an instrument used to measure temperature. It provides a numerical reading that tells us how hot or cold an object or substance is. Different thermometers are designed for different purposes and temperature ranges. The choice of thermometer depends on what is being measured and the required range of measurement.

Traditional thermometers use the change in a physical property of a substance with temperature. For example, in a liquid-in-glass thermometer, a liquid expands when heated and contracts when cooled. This change is shown against a graduated scale and gives the temperature reading.

Types of Thermometers

1. Clinical Thermometer

A clinical thermometer is used to measure the temperature of the human body.

• It is commonly used in medical settings.
• Traditional clinical thermometers generally use mercury, while modern ones are commonly digital.
• The usual human body temperature is around 37°C, though it can vary.
• Traditional clinical thermometers are designed for a relatively narrow range suitable for body-temperature measurement.

2. Laboratory Thermometer

A laboratory thermometer is used to measure the temperature of substances during scientific experiments.

• It has a wider temperature range than a clinical thermometer.
• It can be used to measure the temperature of liquids and other substances in laboratory experiments.
• Unlike a traditional clinical thermometer, it does not have a constriction designed to retain the reading after removal.
• The thermometer should normally be kept in contact with the substance while taking the reading.

3. Digital Thermometer

A digital thermometer uses an electronic temperature sensor and displays the temperature on a digital screen.

• It gives a quick and easy-to-read measurement.
• It does not use mercury.
• Digital thermometers are commonly used for measuring body temperature and in other applications.

4. Other Thermometers

Different types of thermometers are used for specific purposes. Maximum-minimum thermometers are used to record the highest and lowest temperatures over a period, particularly in weather observations. Infrared thermometers measure temperature without direct contact by detecting infrared radiation emitted by an object.

Effects of Heat

When a substance gains or loses heat, its physical condition or temperature may change. The effect of heat depends on the nature of the substance and the amount of heat supplied or removed. Heat can produce several noticeable changes in matter.

1. Rise in Temperature

When heat is supplied to a substance, its temperature generally increases. For example, when water is heated in a vessel, its temperature rises gradually.

The amount of temperature rise depends on the quantity and nature of the substance and the amount of heat supplied.

2. Expansion of Substances

Most substances expand when heated and contract when cooled. This effect is known as thermal expansion.

• Solids generally expand when heated.
• Liquids expand when heated.
• Gases usually show greater expansion than solids and liquids.

For example, railway tracks are provided with small gaps to allow for expansion during hot weather. Similarly, gaps are provided in bridges and expansion joints are used in structures to accommodate thermal expansion.

3. Change of State

Heat can cause a substance to change from one state of matter to another.

For example:

• Ice changes into water when heated.
• Water changes into steam when further heated.
• Steam changes back into water when it loses heat.
• Water can change into ice when sufficient heat is removed.

During a change of state, heat is involved even though the temperature may remain constant for a period. This concept is studied in detail under latent heat and change of state.

4. Change in Volume and Pressure

Heating can cause changes in the volume or pressure of a substance, particularly in gases. When a gas is heated, its particles move more rapidly and may occupy a larger volume if the pressure is allowed to remain constant. If the volume is restricted, heating can instead increase the pressure of the gas.

For example, the pressure inside a closed container containing a gas can increase when the gas is heated.

5. Chemical Changes

In some cases, heat can cause chemical changes in substances. For example, cooking food involves several chemical changes caused by heating. Burning fuels is another example in which heat is produced along with chemical changes.

Thus, heat can produce different effects such as increase in temperature, thermal expansion, change of state, changes in volume or pressure, and certain chemical changes. These effects are important for understanding many natural phenomena and everyday applications.

Units of Heat and Temperature

Heat and temperature are different physical quantities, so they are measured using different units. Heat is a form of energy, while temperature indicates the degree of hotness or coldness of a body.

Units of Heat

Since heat is a form of energy, its SI unit is the joule (J).

Another commonly used unit of heat is the calorie (cal). It is mainly used in some traditional measurements and in nutrition.

• SI unit of heat → joule (J)
• Other commonly used unit → calorie (cal)
• 1 calorie ≈ 4.186 joules
• 1 kilocalorie (kcal) = 1000 calories

For example, when a substance absorbs heat, the amount of energy it receives can be expressed in joules.

Units of Temperature

Temperature is commonly expressed using the Celsius, Fahrenheit and Kelvin scales.

• Celsius → degree Celsius (°C)
• Fahrenheit → degree Fahrenheit (°F)
• Kelvin → kelvin (K)

The kelvin (K) is the SI unit of temperature. Unlike Celsius and Fahrenheit, the Kelvin scale is an absolute temperature scale and its unit is written without the degree symbol.

For example:

• Normal boiling point of water → 100°C
• Normal boiling point of water → 212°F
• Normal boiling point of water → 373.15 K

Understanding the units of heat and temperature is important because they are used throughout the study of heat transfer, specific heat capacity, latent heat and calorimetry.

Heat Transfer

Heat transfer is the process by which thermal energy moves from a body or region at a higher temperature to a body or region at a lower temperature. This transfer takes place because of a temperature difference. Heat transfer continues until thermal equilibrium is reached, when the bodies attain the same temperature.

Heat can be transferred in three main ways: conduction, convection and radiation. The method of transfer depends on the nature of the material and the conditions involved.

1. Conduction

Conduction is the transfer of heat through a substance without the substance as a whole moving from one place to another. It is most commonly seen in solids, especially metals.

For example, when one end of a metal rod is heated, heat gradually travels towards the cooler end. The particles transfer energy to neighbouring particles.

2. Convection

Convection is the transfer of heat through the actual movement of a fluid, such as a liquid or gas. When a fluid is heated, the warmer, less dense portion generally rises and the cooler, denser portion moves down. This produces convection currents.

For example, when water is heated in a vessel, the warmer water rises while cooler water moves downward, producing circulation within the water.

3. Radiation

Radiation is the transfer of heat in the form of electromagnetic waves. It does not require a material medium, so heat can travel through empty space.

For example, heat from the Sun reaches the Earth through radiation.

Comparison of the Three Methods

The three methods of heat transfer are important for understanding many everyday phenomena. Conduction, convection and radiation will be discussed separately in the following topics with their characteristics and examples.

Conduction

Conduction is one of the three methods of heat transfer. It is the process by which heat is transferred from a region of higher temperature to a region of lower temperature through a substance, without the substance as a whole moving from one place to another. Conduction occurs mainly in solids and is especially effective in metals.

When one part of a solid is heated, the particles in that region gain energy and vibrate more strongly. They transfer energy to neighbouring particles, and this process continues from the hotter region towards the cooler region. The particles themselves do not travel from the hot end to the cold end; rather, energy is passed from one particle to another.

Example of Conduction

Consider a metal spoon placed in a cup of hot liquid. The end of the spoon in contact with the hot liquid becomes heated first. After some time, heat travels through the metal and the other end of the spoon also becomes warm. This happens because heat is transferred through the metal by conduction.

Another common example is a metal cooking vessel. When its bottom is heated by a flame, heat travels through the metal and reaches other parts of the vessel.

Conductors of Heat

Materials that allow heat to pass through them easily are called good conductors of heat.

Examples include:

• Copper
• Aluminium
• Iron
• Silver

Metals are generally good conductors of heat, which is why they are commonly used for cooking vessels and other applications where heat needs to be transferred efficiently.

Poor Conductors or Insulators

Materials that do not allow heat to pass through them easily are called poor conductors or thermal insulators.

Examples include:

• Wood
• Plastic
• Rubber
• Air

These materials are useful when we want to reduce or prevent the transfer of heat. For example, the handles of many cooking utensils are made from materials that conduct heat poorly, helping to protect the user from excessive heat.

Important Features of Conduction

• Conduction is most common in solids.
• Metals are generally good conductors of heat.
• Heat is transferred from a higher-temperature region to a lower-temperature region.
• There is no bulk movement of the substance during conduction.
• Energy is transferred from particle to particle through the material.
• Good conductors are useful where efficient heat transfer is required.
• Poor conductors or insulators are useful where heat transfer needs to be reduced.

Convection

Convection is a method of heat transfer in which heat is transferred from one place to another by the actual movement of a fluid. Fluids include liquids and gases. Convection occurs because different parts of a fluid can have different temperatures and densities.

When a fluid is heated, the particles gain energy and move more rapidly. The heated fluid generally becomes less dense and rises, while the cooler and denser fluid moves downward to take its place. This continuous movement produces what are called convection currents. In this way, heat is transferred through the movement of the fluid itself.

Example of Convection in Water

When water is heated in a vessel, the water at the bottom receives heat first. As it becomes warmer, it expands and becomes less dense, so it rises. The cooler and denser water from the upper part moves downward. This water is then heated and rises again. This continuous circulation of water is called a convection current.

Convection in Air

Convection also occurs in gases. When air is heated, it expands, becomes less dense and rises. Cooler air then moves into the space left by the rising warm air.

For example, sea breeze and land breeze occur because land and water heat and cool at different rates. During the day, land becomes warmer more quickly than the sea. The air above the land becomes warm and rises, while cooler air from the sea moves towards the land. This movement of air produces a sea breeze.

Important Features of Convection

• Convection occurs mainly in liquids and gases.
• It involves the actual movement of the fluid.
• Warm fluid generally rises because it becomes less dense.
• Cooler, denser fluid generally moves downward.
• The continuous movement of fluid produces convection currents.
• Convection plays an important role in the heating of liquids and movement of air.
• Sea breeze and land breeze are common examples of convection in the atmosphere.

Radiation

Radiation is a method of heat transfer in which heat energy is transferred in the form of electromagnetic waves. Unlike conduction and convection, radiation does not require a material medium. Therefore, heat can be transferred by radiation through empty space.

The Sun is the most important natural example of heat transfer by radiation. The space between the Sun and the Earth is largely empty, yet the Earth receives heat and light from the Sun through radiation.

How Radiation Takes Place

All objects emit thermal radiation to some extent. The amount of radiation emitted depends on the temperature and nature of the surface. A hotter object generally emits more thermal radiation than a cooler object.

For example, when you stand near a fire, you can feel its warmth even without touching the fire. The heat reaching your body is mainly transferred by radiation.

Examples of Radiation

• Heat from the Sun reaches the Earth through radiation.
• The warmth felt when standing near a fire is partly due to radiation.
• Heat from a hot stove can reach nearby objects without direct contact.
• Infrared radiation is used in some thermal imaging and temperature-measuring devices.

Radiation and Surface Colour

The nature and colour of a surface affect the absorption and emission of radiant heat.

• Dark, dull surfaces are generally good absorbers and emitters of thermal radiation.
• Light-coloured and shiny surfaces are generally poor absorbers and emitters and good reflectors of radiant heat.

This is why the inner surface of some solar cookers is designed to absorb radiation effectively, while shiny surfaces are used where reflection of radiant heat is useful.

Important Features of Radiation

• Radiation transfers heat through electromagnetic waves.
• It does not require a material medium.
• It can occur through vacuum.
• The Sun’s heat reaches the Earth mainly through radiation.
• Dark, dull surfaces generally absorb and emit radiant heat better than light, shiny surfaces.
• Radiation is different from conduction and convection because it does not depend on direct contact or bulk movement of a fluid.

Specific Heat Capacity

Specific heat capacity is an important property of a substance that tells us how much heat energy is required to raise the temperature of a given mass of that substance by a certain amount.

More precisely, the specific heat capacity of a substance is the amount of heat required to raise the temperature of 1 kg of the substance by 1°C (or 1 K) without a change of state.

The amount of heat required depends on the mass of the substance, the change in temperature and the specific heat capacity of the material.

The relationship is: Q = mcΔT

where:

• Q = heat supplied
• m = mass of the substance
• c = specific heat capacity
• ΔT = change in temperature

Example

Suppose equal masses of water and sand receive the same amount of heat. Their temperatures will not necessarily increase by the same amount because water and sand have different specific heat capacities.

Water has a relatively high specific heat capacity. Therefore, it requires a larger amount of heat to raise its temperature by the same amount compared with many common substances. This is one reason why water heats up and cools down relatively slowly.

This property of water has important applications in daily life. For example, water is used as a coolant in some engines because it can absorb a considerable amount of heat without a very large increase in temperature.

Important Points

• Specific heat capacity is a property of a substance.
• It is the heat required to raise the temperature of 1 kg of a substance by 1°C or 1 K.
• SI unit: joule per kilogram per kelvin (J kg⁻¹ K⁻¹).
• A substance with a higher specific heat capacity requires more heat for the same rise in temperature, when the masses are equal.
• Water has a relatively high specific heat capacity.
• Specific heat capacity is different from the total amount of heat absorbed by an object.

Understanding specific heat capacity is useful for explaining why different materials heat up and cool down at different rates.

Latent Heat

Latent heat is the heat energy absorbed or released by a substance when it changes from one state of matter to another, without a change in its temperature. The word “latent” means hidden because this heat is involved in changing the state of the substance rather than increasing its temperature.

For example, when ice is heated at its melting point, it absorbs heat and changes into water. During this change, the temperature of the ice-water mixture remains constant until all the ice has melted. The heat supplied during this process is used to change the state of ice into water.

Similarly, when water reaches its boiling point, it continues to absorb heat while changing into steam. The temperature does not increase during the change of state until the liquid water has completely changed into vapour.

Types of Latent Heat

There are two important types of latent heat:

1. Latent Heat of Fusion

Latent heat of fusion is the heat required to change a substance from a solid to a liquid at its melting point without changing its temperature.

• Ice → Water
• Heat is absorbed during melting.
• The reverse process, water → ice, releases the same type of latent heat.

2. Latent Heat of Vaporisation

Latent heat of vaporisation is the heat required to change a substance from a liquid to a gas at its boiling point without changing its temperature.

• Water → Steam
• Heat is absorbed during vaporisation.
• The reverse process, steam → water, releases heat.

Formula

The amount of heat involved in a change of state is given by:

Q = mL

where:

• Q = heat energy
• m = mass of the substance
• L = specific latent heat

The SI unit of specific latent heat is J/kg.

Example in Daily Life

When sweat evaporates from our skin, it absorbs heat from the body. This removes heat from the skin and produces a cooling effect. This is one reason why sweating helps regulate body temperature.

Latent heat is therefore important in understanding melting, freezing, boiling, condensation and evaporation. The detailed process of change of state is covered separately in the next topic.

Change of State

Matter exists mainly in three states: solid, liquid and gas. A substance can change from one state to another when heat is supplied or removed. This change is called a change of state.

When heat is supplied, the particles of a substance gain energy. Depending on the amount of heat supplied, the substance may change from solid to liquid or from liquid to gas. When heat is removed, the reverse changes can take place.

Change of State and Temperature

During a change of state, the temperature of a pure substance remains constant at a given pressure until the change is complete, even though heat may continue to be supplied or removed. The energy involved in changing the state is associated with latent heat.

For example, when ice at its melting point is heated, it absorbs heat while changing into water. The temperature does not rise until the ice has completely melted.

These changes of state are reversible physical changes in which the substance changes its physical state while its chemical identity remains the same.

Thermal Expansion

Thermal expansion is the increase in the size of a substance when its temperature increases. When a substance is heated, its particles gain energy and generally move or vibrate more vigorously. As a result, the average distance between the particles increases, causing the substance to expand. When the substance is cooled, it generally contracts.

Thermal expansion occurs in solids, liquids and gases, but the amount of expansion is different for each state of matter. Gases generally expand more than liquids, while liquids generally expand more than solids for a comparable temperature change.

Expansion in Solids

Solids can expand in length, area and volume when heated.

• Increase in length → linear expansion
• Increase in area → superficial or area expansion
• Increase in volume → cubical or volume expansion

For example, a metal rod becomes slightly longer when heated.

Expansion in Liquids

Liquids also expand when heated. Since liquids do not have a fixed shape, their expansion is mainly observed as an increase in volume.

A common example is the liquid inside a thermometer. When the temperature rises, the liquid expands and moves up the narrow tube, allowing the temperature to be measured.

Expansion in Gases

Gases generally show greater thermal expansion than solids and liquids. When a gas is heated, its particles move more rapidly and, if the pressure is kept constant, the gas tends to occupy a larger volume.

For example, a hot-air balloon rises because the air inside it is heated, causing it to expand and become less dense than the surrounding cooler air.

Applications of Thermal Expansion

Thermal expansion needs to be considered in the design of many structures and objects.

• Small gaps are provided between railway tracks to allow for expansion during hot weather.
• Expansion joints are provided in bridges and concrete structures.
• Electric wires are not stretched completely tight because their length can change with temperature.
• The liquid in some traditional thermometers expands and contracts with temperature changes.
• Bimetallic strips use the different expansion of two metals and are used in devices such as thermostats.

Calorimetry

Calorimetry is the measurement of the amount of heat transferred during a physical or chemical process. It is used to determine how much heat a substance gains or loses when its temperature changes or when a change of state takes place.

The instrument used for measuring heat transfer is called a calorimeter. A calorimeter is designed to reduce heat exchange with the surroundings so that the heat involved in the experiment can be measured more accurately.

Principle of Calorimetry

The basic principle of calorimetry is based on the conservation of energy. When two bodies at different temperatures are brought into thermal contact in an insulated system, heat lost by the hotter body is equal to heat gained by the colder body, provided there is no significant heat loss to the surroundings.

Heat lost = Heat gained

For a substance whose temperature changes without a change of state, the heat transferred can be calculated using:

Q = mcΔT

where:

• Q = heat transferred
• m = mass of the substance
• c = specific heat capacity
• ΔT = change in temperature

Simple Example

Suppose a quantity of hot water is mixed with a smaller quantity of cooler water in a calorimeter. Heat flows from the hot water to the cooler water. The hot water loses heat, while the cooler water gains heat. After some time, both reach the same temperature. By measuring the masses and temperature changes, the amount of heat transferred can be calculated.

Uses of Calorimetry

Calorimetry is used to:

• Determine the specific heat capacity of a substance.
• Measure the heat released or absorbed during certain processes.
• Study heat changes during physical and chemical reactions.
• Compare the heat-absorbing properties of different materials.
• Determine the energy content of fuels and foods in appropriate calorimetric measurements.

Daily Life Applications

Heat and temperature are involved in many activities and processes that we experience in our daily lives. The principles of heat transfer, thermal expansion, change of state and specific heat capacity help us understand how different objects and materials behave when they are heated or cooled.

Cooking and Heating

Cooking vessels are commonly made of metals such as aluminium or copper because metals are good conductors of heat. They allow heat from the stove to reach the food efficiently. The handles of many cooking vessels are made from materials such as plastic or wood, which are poor conductors of heat and help reduce the transfer of heat to our hands.

Refrigeration and Cooling

A refrigerator removes heat from the inside compartment and transfers it to the surroundings. This keeps food and other items at a lower temperature and slows down the growth of microorganisms and spoilage.

Evaporation also produces a cooling effect. When sweat evaporates from our skin, it takes heat from the body, helping to cool us.

Use of Water as a Coolant

Water has a relatively high specific heat capacity, so it can absorb a considerable amount of heat with a comparatively smaller rise in temperature. Therefore, water is used as a coolant in some engines and industrial systems.

Sea Breeze and Land Breeze

The different rates at which land and water heat and cool lead to changes in air temperature and density. This produces convection currents.

• During the day, land heats up faster than the sea. Warm air above the land rises, and cooler air from the sea moves towards the land. This is called a sea breeze.
• At night, land cools faster than the sea. Air above the relatively warmer sea rises, and cooler air from the land moves towards the sea. This is called a land breeze.

Thermal Expansion in Railway Tracks and Bridges

Materials expand when heated and contract when cooled. Therefore, small gaps or expansion joints are provided in railway tracks, bridges and other structures to allow for changes in size due to temperature variations.

Thermos Flask

A thermos flask is designed to reduce heat transfer between its contents and the surroundings. Its construction reduces heat transfer by conduction, convection and radiation, helping hot liquids remain hot and cold liquids remain cold for a longer period.

Woollen Clothes in Winter

Wool is a poor conductor of heat and can trap air within its fibres. Air is also a poor conductor of heat. Therefore, woollen clothes reduce the loss of body heat to the colder surroundings and help keep us warm.

Solar Energy

The Earth receives heat from the Sun mainly through radiation. Solar cookers and solar water heaters make use of solar radiation to heat materials or water without direct contact with the Sun.

These examples show how the principles of heat and temperature are applied in cooking, cooling, construction, weather phenomena, clothing, household appliances and energy use in everyday life.

Conclusion

A clear understanding of these basic principles helps TNPSC aspirants answer questions related to heat, temperature and their everyday applications. Regular revision of definitions, units, important concepts and examples can make this topic easier to remember and useful for examination preparation.

Further References

For additional reading and conceptual understanding for Science Topics, learners can refer to:

• NCERT Class 7 Science – Heat — directly relevant to heat, temperature, measurement of temperature and modes of transfer of heat.
• NCERT Science Exemplar – Unit 4: Heat — useful for additional practice and conceptual revision on Heat.