Heat: Heat is a form of energy produced due to the random motion of molecules constituting the body. Heat is measured in terms of its S.I. unit – joule (J). Heat also has other units like calorie (cal) and kilocalorie (kcal). Joule and calorie are related to each other as follows:

1 cal = 4.186 J ~ 4.2 J

Temperature: A quantity that tells about the thermal state of the body is called Temperature. Temperature also helps determine the direction of heat flow when two bodies having different temperatures are placed in contact. Temperature is measured in terms of its S.I. unit – kelvin (K). The most commonly used unit of temperature is degree Celsius (0C). Kelvin and degree celsius are related to each other as follows:

Tk = 273 + t0C

You must have seen that substances expand when they are being heated. This happens because the density decreases when materials are heated and vice versa when cooled down. Let us now consider the case of water.

Generally, cold water remains unchanged until 40C. As we cool the water, its density gradually increases. As it reaches 4oC, the density reaches its maximum point. What happens next is quite surprising. If you try to cool the water further, to turn it into ice (00C), water will expand and drop its temperature. That is, the density of water will decrease when you cool it down from 40C to 00C. This is called the anomalous expansion of water.

Global warming is a gradual increase in Earth’s temperature, usually due to the greenhouse effect, which results from increased levels of CFCs, carbon dioxide, and other pollutants. A phenomenon like global warming has changed the climatic pattern of the earth. 

There are a few causes of this phenomenon that harms plants, animals, and humans. The causes of global warming are classified as human-made and natural. 

1. Man-made causes: Deforestation, chlorofluorocarbon, vehicles, agriculture, industrial development, overpopulation, etc. 
2. Natural Cause: Water vapour, volcanoes, forest blazes, melting permafrost, etc. 

The Greenhouse Effect is one of the reasons which leads to global warming. Understanding the greenhouse effect is equally important because global warming and greenhouse effects are related to each other. In a greenhouse, the plants require a warm temperature to grow. 

A greenhouse is almost entirely made up of glass. Hence, the heat is retained, which helps the plants to thrive. The temperature in the greenhouse gets higher than the temperature outside the greenhouse. This is called the greenhouse effect.

Thermodynamics deals with the movement of energy from one form to another form. It gives the relationship between temperature and heat with work done and energy. Given below are the laws of thermodynamics:

1. The first law of thermodynamics: This law is associated with the law of conservation of energy. It states that energy is always conserved. It can neither be created nor destroyed but can be transferred from one form to another form. 
2. The second law of thermodynamics: There exists a useful state variable called entropy S. The change in entropy delta S is equal to the heat transfer delta Q divided by the temperature T.
3. Third law of thermodynamics: At absolute zero, the entropy of a perfect crystal is zero.
4. Zeroth Law: If both the two systems are in thermal equilibrium with a third system, then all three of them are in thermal equilibrium with each other.

The energy sources can be commercial or non-commercial.

• Commercial entities usually consume commercial energy. It is accessible to the consumers at a price to be paid. It is a non-renewable source of energy. It is usually not used by households and residents. Commercial sources like electricity, coal, and petroleum are bought and sold to users. 
• Non-commercial energy is used for household purposes by people and is available free of cost. It marks the standard of living of a country. Example: firewood, cow dung, agricultural waste, etc.

Renewable Sources Of EnergyNon-Renewable Sources Of EnergyThe resources which can be renewed are called renewable sources of energy.The resources which cannot be renewed once consumed are called non-renewable sources of energy.These resources do not harm the environment in terms of pollution. These resources create pollution and harm the environment. These resources are inexhaustible. These resources are exhaustible. These resources do not get affected by any kind of human activity.These resources get affected by human activity. Example: Water, Air, Solar energy.Example: Oil, Mineral, Coal.

1. What is heat and its S.I. unit?
2. A: Heat is a form of energy produced due to the random motion of molecules constituting the body. Heat is measured in terms of its S.I. unit – joule (J).
3. Which substances expand when heated? Give examples.
4. A: Iron and brass are two examples of substances that expand on heating.
5. What is a system in thermodynamics?
6. A: It is a body of ration or/and matter, confined in space by the walls. It separated from the surroundings with defined permeabilities.
7. Is the sun renewable or non-renewable energy?
8. A: Sun is renewable energy.
9. What is an anomalous expansion of water?
10. A: The expansion of water when it cooled down from 4oC to 0oC is the anomalous expansion of water.