Heat
Heat is a form of energy that makes things feel hot or warm. When something is hot, it has a lot of heat energy, and when something is cold, it has less heat energy. Heat can move from a hot object to a cooler object, and this transfer of energy is what makes things feel hot or cold.
Measuring Temperature:
Temperature is a measure of how hot or cold something is. We use a device called a thermometer to measure temperature. There are different types of thermometers, such as clinical thermometers used to measure body temperature, and laboratory thermometers used for other objects and substances.
Transfer of Heat:
Heat can be transferred in three ways: conduction, convection, and radiation. Conduction is the transfer of heat through a material, like when a metal spoon gets hot when placed in hot soup. Convection happens in liquids and gases, where heated molecules rise and cooler ones replace them. Radiation is the transfer of heat through electromagnetic energy waves, like the heat we get from the sun.
Absorption of Heat:
Different colors can absorb different amounts of heat. Dark colors, like black, absorb more heat, which is why we feel comfortable wearing them in winters. Light colors, on the other hand, reflect heat, making us feel comfortable wearing them in summers. Woolen clothes can trap air and prevent heat from escaping, keeping us warm in winter.
Difference Between Heat and Temperature:
Heat is the energy stored in an object, while temperature is a measure of how hot or cold that object is. Heat depends on factors like mass and material, while temperature is related to the kinetic energy of the object’s particles.
Radiation:
Radiation is the process through which we get heat energy from the sun. Unlike conduction and convection, radiation can travel through space and doesn’t require a medium for transmission.
Disadvantages of the Celsius Scale:
The Celsius scale can go below zero degrees Celsius, which can be a disadvantage in certain situations. Additionally, it doesn’t directly correspond to changes in the volume and pressure of gases.
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FAQ
Give two examples each of conductors and insulators of heat.
Conductors of heat: Metals like copper and aluminum are good examples of conductors of heat as they allow heat to pass through them easily.
Insulators of heat: Materials like wood and plastic are good examples of insulators of heat as they do not allow heat to transfer through them easily
3. Fill in the blanks : (a) The hotness of an object is determined by its __________. (b) Temperature of boiling water cannot be measured by a _____________ thermometer. (c) Temperature is measured in degree ______________. Rationalised 2023-24 HEAT 35 (d) No medium is required for transfer of heat by the process of __________. (e) A cold steel spoon is dipped in a cup of hot milk. Heat is transferred to its other end by the process of ______________. (f ) Clothes of ______________ colours absorb more heat better than clothes of light colours.
(a) The hotness of an object is determined by its "temperature."
(b) Temperature of boiling water cannot be measured by a "clinical" thermometer.
(c) Temperature is measured in degree "Celsius" (°C).
(d) No medium is required for transfer of heat by the process of "radiation."
(e) A cold steel spoon is dipped in a cup of hot milk. Heat is transferred to its other end by the process of "conduction."
(f) Clothes of "dark" colours absorb more heat better than clothes of light colours
Match the following : (i) Land breeze blows during (a) summer (ii) Sea breeze blows during (b) winter (iii) Dark coloured clothes are preferred during (c) day (iv) Light coloured clothes are preferred during (d) night
(i) Land breeze blows during (b) winter (ii) Sea breeze blows during (a) summer (iii) Dark-colored clothes are preferred during (c) day (iv) Light-colored clothes are preferred during (d) night
Discuss why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing .
Wearing more layers of clothing during winter keeps us warmer because the air trapped between the layers acts as an insulator, preventing heat from escaping our body, whereas a single thick piece of clothing may not trap enough air and allow heat to dissipate more quickly.
In places of hot climate it is advised that the outer walls of houses be painted white. Explain.
In places of hot climate, painting the outer walls of houses white is advised because white reflects sunlight and heat. When sunlight falls on a white surface, it is mostly reflected back, rather than being absorbed. As a result, the white walls of houses do not absorb as much heat, keeping the interior cooler. This helps in reducing the amount of heat that enters the house, making it more comfortable and energy-efficient, especially during hot weather.
One litre of water at 30°C is mixed with one litre of water at 50°C. The temperature of the mixture will be (a) 80°C (b) more than 50°C but less than 80°C (c) 20°C (d) between 30°C and 50°C
The temperature of the mixture will be (b) more than 50°C but less than 80°C.
To find the final temperature of the mixture, we can use the principle of the conservation of energy, which states that the total heat energy before the mixing is equal to the total heat energy after the mixing.
An iron ball at 40°C is dropped in a mug containing water at 40°C. The heat will (a) flow from iron ball to water. (b) not flow from iron ball to water or from water to iron ball. (c) flow from water to iron ball. (d) increase the temperature of both.
(b) not flow from iron ball to water or from water to iron ball.
Stainless steel pans are usually provided with copper bottoms. The reason for this could be that (a) copper bottom makes the pan more durable. (b) such pans appear colourful. (c) copper is a better conductor of heat than the stainless steel. (d) copper is easier to clean than the stainless steel
(c) copper is a better conductor of heat than the stainless steel.
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