# General Science

#### Image Formation in Plane Mirror

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.

#### Formation of Images Due to Reflection

To see an object or image, the light from it should reach to the eyes of the observer. It means light coming from an object or image should fall on retina where from it will be sensed by brain with the help of optical nerves.

#### Laws of Reflection of Light

Suppose a ray of light (IO) falls on a reflecting surface AB at O, after reflection it goes along OR. The reflection of light from the surface takes place according to the following two laws.

#### Reflection of Light

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.

#### Specific Thermal Capacity of Material

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.

#### Thermal Expansion

Every material (except water which contracts on heating from 0°C to 4°C) expands on heating. The increase in the size of a body on heating is called thermal expansion.

#### Effects of Heat

When a body is heated changes may occur in some of its properties .These changes are the effects of heat.

#### Measurement of Temperature (Thermometer)

Whenever a patient is brought to a doctor, the doctor normally measures his body temperature. The device the doctor uses to measure the body temperature is thermometer. There are different types of thermometers for different purposes.

#### Heat and Temperature

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.

#### Power

Power is a quantity which tells how fast the work is done. Power is defined as the time rate of doing work i.e., the amount of work done in unit time.

#### Energy Transformation and Conservation

The various forms of energy mentioned get converted from one form to another in different situations. This phenomenon of converting one form of energy to another form is called energy transformation.

#### Different Forms of Energy

You do work by spending muscular energy which you gain from the chemical energy of the food you eat. The fan runs on electrical energy. While playing with magnets, you might have seen that a magnet can move a piece of iron so it has magnetic energy.

#### Energy and its Relation with Work

When you do work, you spend energy and more energy is required to do more work. The capacity of a body to do work is determined by the energy possessed by it.

#### Relation Between Work, Force and Displacement

Work is measured as the product of force and the displacement in the direction of the force.

#### Work

Force changes the motion (momentum). But during the change in motion, the body on which the force is applied also moves through some distance. This leads to some more basic concepts of science - work, power and energy.

#### Transformation of Energy

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 Energy

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.

#### Energy from Biomass

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.

#### Ocean Energy

The ocean is also a powerful source of renewable energy. The energy of the ocean can be harnessed in three basic ways: using wave power, using tidal power, and using ocean water temperature variations.

#### Geothermal 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.

#### Hydroelectric Energy

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 Energy

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.

#### Solar Energy

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.

#### Renewable Energy Sources

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.

#### Nuclear Energy: Energy from the Atom

The atoms of a few elements such as radium and uranium act as natural source of energy. Atoms of these elements spontaneously undergo changes in which the nucleus of the atom disintegrates.

#### Non Renewable Energy Sources

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.

#### Natural Gas

Natural gas is another major source of the energy. Oil and gas fields have been found everywhere on the planet except on the continent of Antarctica. These fields always contain some gas, but this natural gas (methane) does not take nearly as long to form.

#### Coal

Coal is formed in a way similar to the other fossil fuels, though it goes through a different process called coalification. Coal is made of decomposed plant matter in conditions of high temperature and pressure, though it takes a relatively shorter amount of time to form.

#### Introduction to 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.

#### Buoyancy and Archimedes' Principle

A mug filled with water appears to be heavier when it is lifted from bottom of the bucket to above the surface of water than the mug within the water in the bucket.

#### Mass and Weight

Mass of a body is the quantity of matter contained in the body. Mass of an object is constant and does not change from place to place. It remains the same whether the object is on earth, on moon or anywhere in outer space.

#### Motion of an Object Under Gravity

The g is constant near the surface of earth. Therefore, all the equations for uniformly accelerated motion of bodies become valid when acceleration a is replaced by g.

#### Acceleration Due to Gravity

The speed of a falling stone increases continuously. The stone is accelerated due to force of attraction between the stone and the earth. This acceleration is called the acceleration due to gravity.

#### Newton's Law of Gravitation

Newton expressed the law of gravitation in the language of mathematics.

#### Force of Gravitation

A force is required to change the state of rest or of motion of a body. All objects when dropped from a height fall towards the earth. Why do objects fall towards the earth?

#### Environmental Problems

Environmental problems arise both due to natural processes and human activities. These problems adversely affect human and other forms of life.

#### Natural Environment

All living and non-living things that occur naturally on earth constitute the natural environment. All living organisms are dependent on the environment for their survival. Their life is regulated by the environment and in turn they influence the environment.

#### Water

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.

#### Air

Air is a mixture of gases and is one of the main abiotic components of the environment. Air is an extremely important natural resource, as living organisms breathe in air. Air is found everywhere. Air in motion is called wind. It is also present in water and soil.

#### Health and Hygiene

According to the World Health Organization (WHO), health is a State of complete physical, mental and social well being and not merely the absence of disease. It means proper functioning of the body and the mind.

#### Food and Nutrition

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.

#### Heredity

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.

#### Reproduction

Reproduction is defined as the biological process by which organisms give rise to their own kind. Reproduction may occur in two ways:

#### Nervous System: Control and Coordination

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.

#### Digestion, Transportation, Respiration & Excretion

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.

#### Cells and Tissues

The invention of microscope helped in the discovery of the cells. Robert Hooke discovered the cell in 1665. Soon a cell theory was formulated.

#### Living Organisms

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.

#### Materials: Metals and Non-Metals

Elements can be broadly divided into two categories: metals and non-metals. They differ both in physical and chemical properties.

#### Physics Scientific Reasons

An object immersed in water appears lighter. Why?

When an object is immersed in water it experiences an upthrust exerted by water in upward direction. Hence, it appears light in weight.

#### Sound and Communication

Sound is a result of vibration. The vibration is produced by a source, travels in the medium as a wave and is ultimately sensed through the ear - drum.