ICSE Class 8 Physics Chapter 05 More About Energy

More About Energy

Learning Outcomes

Sources of energy: renewable and non-renewable

Solar energy

Biomass

Wind energy

Geothermal energy

Tidal energy

Hydroelectric energy

Fossil fuels

Air pollution

Nuclear energy

Conservation of energy

Fact File

Ancient people used energy from fire to cook, energy from mice to develop tools, energy from wind to move their boats, and energy from waterwheels for irrigation. Ancient Romans heated their public baths by running water over sun-exposed black tiles.

What Is Energy?

Do you notice any difference in yourself when you wake up in the morning and when you go to bed at night? In the morning, you are full of energy and feel fresh, while at night you feel tired and exhausted as your energy gets used up during the day in all your activities. What does this energy mean? You have studied it in earlier classes. Do you remember what energy is?

Energy is the ability to do work.

Energy is all around you everyday. Without energy there would be nothing - no wind, no rivers, and no life at all. Every object in our surrounding is full of energy. This energy exists in different forms such as potential energy, kinetic energy, solar energy, light energy, chemical energy, etc. In order to use all these energies efficiently, we need to change one form of energy to another. We call this transformation of energy. You might have studied about this in class 6.

In this chapter, you will learn about the various sources of energy, their advantages and disadvantages, and how they are useful to us.

Teacher's Note

Energy powers everything we do - from charging our phones to heating our homes. Ask students to observe and list all the energy transformations they experience in a single day.

Sources Of Energy

All forms of energy that we see are stored in different energy sources that we use everyday. These sources are divided into two groups - renewable and non-renewable sources of energy.

You might be using LPG (cooking gas), petrol, kerosene, and coal in your day-to-day life. Do you know that these sources of energy are limited and they take a lot of time, over millions of years, to form? These resources, once used, cannot be replenished within a short period of time and will be lost forever. Such sources of energy are called non-renewable sources of energy. Even nuclear power and minerals like uranium, etc. are non-renewable sources of energy. However, other forms of energy that we get from sources like the sun, water, wind, tides, and biomass are continuously replenished through a number of natural phenomena. So, such resources are called renewable sources of energy.

Let us learn about all these non-renewable and renewable sources of energy in detail.

Teacher's Note

Help students understand that renewable resources like solar and wind can be used indefinitely, while fossil fuels are being depleted. Have them research which energy sources their local region relies on.

Renewable Sources Of Energy

Solar Energy

We know that the sun is the ultimate source of all energy. But the solar energy that reaches our earth is in a diffused form. i.e., the solar energy falling on a unit area of the earth's surface is very small. Thus, special devices called solar collectors are used to collect the solar energy over large areas and change it into a storable and usable form. Some devices that use solar energy directly for some day-to-day functions are mentioned here.

Solar cooker: is a device which uses solar energy for cooking food. It is made of an insulated wooden box painted black from inside and has a glass cover on top. A plane mirror attached to the box reflects sunlight. The food to be cooked is kept in containers, painted black from outside, inside the box. Since food in a solar cooker is cooked at low heat, the nutrients are not destroyed. Also, this saves fuel like LPG (non-renewable) and does not produce smoke.

Solar photovoltaic cell: is a device that is used to convert solar energy into electrical energy by generating a potential difference. A solar cell is made of materials, like silicon, and is used in calculators, watches, and transistor radios where a very small amount of current is required. To generate a large amount of current, a number of solar cells are connected together forming a solar panel.

Benefits and problems of solar energy

The use of solar cells is fast becoming more economical. Even though they are expensive, they are useful in remote areas where it is cheaper to build solar panels than to run power lines. They power irrigation pumps, telephone booths, and aircraft navigation beacons. Solar panels also provide power to satellites, spacecrafts, and sometimes to isolated buildings. Solar energy is renewable and non-polluting. However, solar cells and collectors are costly. Also, solar energy can be used to make electricity only in places that get enough sunlight everyday. So, people are working on new kinds of solar cells that work with less sunlight and are less expensive.

Teacher's Note

Solar energy is increasingly powering homes and schools worldwide. Show students pictures of solar panels on rooftops and discuss why sunny regions are better suited for this technology.

The Big Solar Pond At Bhuj

One way to trap solar energy is through the use of solar ponds. A solar pond collects and stores energy on a large scale in the bottom layer where there is dissolved salt. It can be used for water desalination, drying, and power generation. Apart from being cost-effective, solar ponds can be used for reducing the consumption of fossil fuels and bringing down pollution.

The solar pond at Bhuj, Gujarat is one of the largest operating solar ponds in the world. This pond has been successfully supplying processed heat since September, 1993. Some towns in Israel get their energy from solar ponds on the Dead sea. These ponds generate 5 MW of electricity, enough for a small town.

Biomass (Bio Energy)

Have you ever come across the term biomass? Do you know what it means? Biomass means biological mass, which constitutes both plants and animals. Biomass collectively refers to plants, animals, industrial waste, wood, sewage, crop residue, cow dung, and other wastes. It is a rich renewable source of energy but is underutilized. Biomass, like wood, cow dung, etc., is usually burnt in air to obtain heat. However, this is not an efficient method of getting energy. An efficient method is to convert biomass into biogas, a gaseous fuel. This is done in a biogas plant. Biomass is mixed with water and kept in a tank, which has no supply of air. In the absence of air, biomass mixed with water forms methane, carbon dioxide, and other gases. This mixture of gases is called biogas. After the formation of biogas, the residue left behind serves as a good fertilizer.

Table 5.1 shows the composition of biogas.

Biomass fuel used in India accounts for about one-third of the total fuel used in the country, being the most important fuel used in over 90% of the rural households and about 15% of the urban households.

Teacher's Note

Biogas plants transform agricultural and animal waste into clean cooking fuel while producing fertilizer. Discuss how this technology could help rural communities reduce deforestation and improve sanitation.

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