To understand the formation of image, you may consider the light rays emerging out of the object A. The three rays namely (a), (b), and (c) after striking the mirror M1M2 get reflected in the direction (d), (e) and (f), respectively obeying the laws of reflection.
Light is the common form of energy. It makes the objects visible to us. When you see an object you do so because light from the object enters in your eyes. Some objects such as sun, stars, burning candles, lamp, etc. which emit light by their own are called luminous objects.
When two bodies at different temperatures are kept in contact, heat is transferred from the hot body to the cold body till both of them acquire the same temperature. The two bodies then are called in thermal equilibrium. In acquiring thermal equilibrium the hot body loses heat and the cold body acquires an equal amount of heat.
One of the most common forms of energy is thermal energy. It is the energy due to which we feel hot or cold. If the energy flows into our body we feel hot and if it flows out of our body we feel cold. To prevent heat from flowing out of our body we wear woolen clothes during winter.
Energy can exist in many different forms. Energy can be changed from one form to another. But it cannot be created or destroyed. It just gets transformed into another form. Eventually, most of it ends up as heat, but it is so spread out that it cannot be detected or used.
Hydrogen could be a very environmentally friendly source of energy in the future. In the long-term, hydrogen is likely to reduce dependence on conventional sources of energy such as petrol, diesel and coal. In addition to it, the use of hydrogen as source of energy will help in reducing the emission of greenhouse gases and other pollutants.
The biomass is organic material made from plants and animals. It includes garbage, industrial waste, crop residue, manure, wood, sewage and dead parts of living objects. Like all other sources of energy, it also contains stored energy from the sun. Therefore, biomass is also a very good source of energy.
Geothermal energy is another alternative source of energy. Geothermal energy is obtained from the internal heat of the earth. It is one of the oldest types of natural sources of heat. It dates back to Roman times, when the heat from the earth was used instead of fire, to heat rooms and warm water for baths.
Like wind energy, the flowing water and water stored in huge dams is also a very important source of energy which is known as hydroelectric energy. But, overdevelopment and unrestricted harnessing of water power can have a devastating effect on the local environment and habitation areas.
Wind power is another alternative energy source that could be used without producing by-products that are harmful to nature. Like solar power, harnessing the wind is highly dependent on weather and location. However, it is one of the oldest and cleanest forms of energy and the most developed of the renewable energy sources.
The sun has been providing heat and light for billions of years and it is expected that it will continue to do so for billions of years to come. All plants get their energy from the sun and all animals get their energy mainly from the plants. Therefore, the sun is a source of energy for animals.
The fossil fuels such as coal, oil and natural gas meet most of the energy needs of the world today. But what will happen when the reserves of these non-renewable sources of energy get completely exhausted? We also need to pay attention to the damaging effects of fossil fuels on the environment.
Petrol and diesel extracted from crude oil are commonly used to run different kinds of vehicles, such as cars, buses, tractors, trucks, trains, and aeroplanes. Similarly, kerosene and natural gas are used as fuels in lamps and stoves. Crude oil, coal and natural gas occur in limited and exhaustible quantities. They cannot be regenerated in a short period of time or used again and again. Hence, they are called non-renewable sources of energy.
We take food for survival and growth of our body. Vehicles like motorcycles, tractors, buses, trucks, ships and aeroplanes require fuel for their running. Even for cooking food we require fuel. What is important which we get from the food or from the fuel? It is the energy.
Water is the most important substance needed for survival of living beings. Living beings cannot live long without water. Water is available in plenty on earth. More than three-fourth of the earth’s surface is covered with water in the form of seas, rivers and lakes. It is also found inside the earth’s crust Most of the water that we get from the wells comes from this source.
The sources of food are broadly classified into two groups - plants and animals. Humans consume everything from fruits, flowers and even the stem of some plants. Leaves and stem like lettuce, celery, etc; roots of some plants like carrots, beetroot, etc. and seeds like wheat, rice, etc. All food come from plants as even the animals depend on plants. Hence, the source of all food in this world are plants, directly or indirectly.
The passing down of similar characters generation after generation is termed heredity. Heredity is controlled by genes. Differences in gene combinations lead to variations or differences even among members of the same family. The science of heredity and variation is termed Genetics.
The nervous system and the endocrine system ensure that the body works in a controlled and coordinated manner. The nervous system includes the brain, spinal cord, sense organs and nerves while the endocrine system operates through certain chemicals called hormones which are produced by specialized glands and are secreted directly into the blood. The nervous system works with the endocrine system to communicate, integrate and coordinate the functions of various organs and systems in our body.
The activities by which living organisms take in food, derive energy, remove waste from their body and respond to changes in the environment are called life processes.
Biodiversity is the enormous variety of organisms is termed biodiversity (bios means life and diversity means variety). There is diversity in size among organisms and in complexity. For example, bacteria are simple single celled organisms and humans are made of a trillion cells and are highly complex.
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