Unit - 4 Heat
Unit - 4
Heat
Summary
1. The sun, biofuels, electricity and fossil fuels are the main sources of heat.
2. Solar heat warms the environment, heats water and produces electricity.
3. Wood, straw, straw, organic gas etc. are biofuels.
4. Coal, petrol, diesel, kerosene, etc. obtained from mines are called biofuels. E
5. Heat changes the state and volume of matter.
6. Dark and black colored clothes dissipate heat faster than pale and light colored clothes.
7. Heat is used to warm the body, cook food, dry clothes and other items,
It is used in activities such as purifying water, producing goods in factories.
Fill in the blanks:
- (a) The sun is the main source of heat.
- (b) Water is heated by solar oven.
- (c) Firewood, straw, straw etc. are called as renewable fuel.
- (d) Coal, petrol etc. are called non-renewable fuel.
- (e) Heat changes the state and temperature of matter.
- (f) When water is heated it becomes steam.
- (g) When the air is heated, pressure increases.
Choose the correct one from the given answers:
(a) Which is a fossil fuel?
- Firewood
- Coal
- Bio gas
- Gui“tha
(b) Which color of cloth absorbs the most heat?
- Black
- White
- Green
- Red
(c) Which of the following changes in temperature?
- Steam to water
- Water to ice
- Steam to ice
- Ice to water
(d) Which is a biofuel?
- Natural gas
- Coal
- Chhwali
- Crude oil
(e) Which is not a source of heat?
- Moon
- Sun
- Coal
- Electricity
(f) Where is natural gas obtained from?
- By mining
- By air
- By rotting dung
- By burning firewood
Write the answers to the following questions:
(a) Why is the sun considered the main source of heat? The sun is the main source of heat because it is the only star in our solar system that produces its own light and heat. The sun's energy is essential for life on Earth, as it provides the energy needed for plants to grow and for animals to survive.
(b) What is biofuel? Biofuel is a renewable energy source that is made from organic matter, such as plant or animal waste. Biofuel can be used to power vehicles, generate electricity, and heat homes and businesses.
(c) What is the name of the device that produces heat from electricity? The name of the device that produces heat from electricity is a heater. Heaters are used to warm homes and businesses, and they can also be used to cook food and heat water.
(d) What is the effect of heat on matter? Heat can cause matter to change its state, temperature, and volume. When heat is applied to a solid, it can cause the solid to melt, vaporize, or decompose. When heat is applied to a liquid, it can cause the liquid to evaporate or boil. When heat is applied to a gas, it can cause the gas to expand or contract.
(e) What happens when water is heated? When water is heated, it changes from a liquid to a gas, or steam. The temperature at which water boils is 212 degrees Fahrenheit.
(f) Mostly black color clothes in winter months and white color clothes in summer It is worn, why? Black clothes absorb more heat than white clothes, so they are worn in the winter to help keep people warm. White clothes reflect more heat than black clothes, so they are worn in the summer to help people stay cool.
(g) What should be done to purify the water for drinking? Give suggestions. There are many ways to purify water for drinking. Some common methods include:
- Boiling the water for one minute.
- Adding chlorine bleach to the water at a rate of 4 drops per gallon.
- Using a water filter.
(h) Clothes dry slowly in the shade but dry quickly in the sun, why? Clothes dry slowly in the shade because the sun's heat is not available to evaporate the water from the clothes. Clothes dry quickly in the sun because the sun's heat evaporates the water from the clothes quickly.
(i) Write two reasons for eating most foods cooked. There are two main reasons for eating most foods cooked:
- Cooking kills harmful bacteria that can cause food poisoning.
- Cooking makes food more digestible and easier to absorb nutrients.
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