General Science

Environmental Problems

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

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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.

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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.

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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.

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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.

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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.

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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.

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Reproduction

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

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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Light

Reflection of Light

Some objects such as sun, stars, burning candles, lamp, etc. which emit light by their own are called luminous objects. Some other objects may bounce back a part of the light falling on them from any luminous object. This bouncing back of light after falling on any surface is called reflection of light.

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Heat

Temperature is a measure of the degree of hotness of an object. Thermometer is a device used for measuring temperatures. Clinical thermometer is used to measure our body temperature. The range of this thermometer is from 35°C to 42°C. For other purposes, we use the laboratory thermometers. The range of these thermometers is usually from -10°C to 110°C. The normal temperature of the human body is 37°C.

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Magnetism

When electric current passes through current carrying conductor or coil then a magnetic field is produced around it. Opposite to this is if a continuous change in magnetic field is produced then electric current can be produced.

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Electricity

A plastic comb when brought near a piece of paper does not pick up small pieces of a paper. But if you comb your dry hair and bring the comb close to a small piece of paper, you will notice that the bits of paper are attracted towards the comb. This happens because the comb gets charged or electrified when you comb your dry hair.

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Properties of Solids and Fluids

Fluid Pressure is the force acting normally on unit area of a surface due to a fluid is called the fluid pressure.

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Gravitation

While Newton was sitting under an apple tree, an apple fell on him. The fall of the apple set Newton thinking, why did the apple fall down? If some force is acting on the apple then it must be in accelerated motion.

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Motion

Motion is a continuous change in the position of the object with respect to the observer.

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Conservation of Momentum

Law of conservation of momentum is a very important law of science. According to this law, if two or more objects collide with each other, their total momentum remains conserved before and after the collision provided there is no external force acting on them.

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Newton's Third Law of Motion

Newton in his third law of motion stated a relation between action and reaction. According to this law, to every action there is an equal and opposite reaction.

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Newton’s Second Law of Motion

According to Newton’s first law of motion the application of an unbalanced force brings a change in the velocity of an object. Thus, the force can produce a change of momentum. Newton’s second law of motion establishes a relationship between force and change in momentum.

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Momentum

The force required to stop a moving body depends upon its mass. Suppose two balls of same mass are moving with different velocities. Which ball will need more force to stop? The faster moving ball require more force to stop it. Thus, the force required to stop a body also depends upon its velocity.

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Newton's First Law of Motion

An object offer resistance to change in its state of motion. This was studied by Newton in detail and he presented his findings in the form of three fundamental laws that govern the motion of objects.

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Inertia

The inertia is the tendency of objects to stay at rest or to keep moving with the same velocity.

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Meaning of Force

If you place a ball on a flat surface, it will remain there until unless you disturb it. It will move only when either you push it or pull it. This push or pull acting on an object is known as a force.

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Uniform Circular Motion

Consider the motion of an object along a circular track of radius R through four points A, B, C and D on the track. If object completes each round of motion in same time, then it covers equal distance in equal interval of time and its motion will be uniform motion.

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Equations of Motion

Consider an object moving with uniform acceleration, a. Let u be the initial velocity (at time t = 0), v, velocity after time t and S, displacement during this time interval. There are certain relationships between these quantities.

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Acceleration

In the non-uniform motion, the change in velocity in different intervals of motion is different. This change in velocity with time is called acceleration.

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Velocity-Time Graph

Take time on the horizontal axis and velocity on the vertical axis on a graph paper. Let one division on horizontal axis represent 1 s and one division on vertical axis represent 10 ms–1.

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Position-Time Graph

It is easy to analyze and understand motion of an object if it is represented graphically. To draw graph of the motion of an object, its position at different times are shown on y-axis and time on x-axis.

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Average Speed and Average Velocity

Speed during a certain interval of time can not be used to determine total distance covered in given time of the journey and also the time taken to cover the total distance of journey. It is because a body does not always travel equal distance in equal interval of time.

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Velocity

When motion is along the shortest path, it is directed from the point of start to the point of finish. How fast this motion is determines the velocity. The velocity is the ratio of length of the shortest path (displacement) to the time taken.

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Speed

The measure of how fast motion can take place is the speed. Speed can be defined as the distance traveled by a body in unit time.

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Distance and Displacement

For a moving object two points are significant. One is the point of start or origin where from the object starts its motion and the other is the point where it reaches after certain interval of time. Points of start and destination are connected by a path taken by the object during its motion.

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Motion and Rest

If you observe a moving bus, you will notice that the position of bus is changing with time. This means that the bus is in motion. Now suppose you are sitting in a bus moving parallel to another bus moving in the same direction with same speed. You will observe that the position of the other bus with respect to your bus is not changing with time. In this case the other bus seems to be at rest with respect to your bus.

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Bleaching Powder

Bleaching is a process of removing colour from a cloth to make it whiter. Bleaching powder has been used for this purpose since long. Chemically, it is calcium oxychloride, CaOCl2.

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Plaster of Paris

Also called POP, chemically it is 2CaSO4.H2O or CaSO4.½H2O (calcium sulphate hemi hydrate).

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Washing Soda

Washing soda is used for washing of clothes. It is mainly because of this chemical that the clothes washed appear so white. Chemically, washing soda is sodium carbonate decahydrate, Na2CO3.10H2O.

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Baking Soda

Chemically baking soda is sodium hydrogen carbonate, NaHCO3.

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Formation of Salts

Salts are ionic compounds made of a cation other than H+ ion and an anion other than OH ion. Salts are formed in many reactions involving acids and bases.

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Importance of pH in Everyday Life

pH plays a very important role in everyday life - (i) pH in Humans and Animals, (ii) Acid Rain, (iii) pH in Plants, (iv) Digestive System, (v) Self Defence of Animals and Plants, and (vi) Tooth Decay.

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pH Scale

The pH scale ranges from 0 to 14. On this scale, pH 7 is considered neutral, below 7 acidic and above 7 basic. Farther from 7, more acidic or basic the solution is.

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pH and its Importance

When dealing with range of concentrations (such as these of H+ (aq) ions) that spans many powers of ten, it is convenient to represent them on a more compressed logarithmic scale. By convention, we use the pH scale for denoting the concentration of hydrogen ions.

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Neutral, Acidic and Basic Solutions

In pure water H+ (aq) and OH (aq) ions are produced in equal numbers as a result of dissociation of water and therefore, their concentrations are also equal.

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Self Dissociation of Water

Water plays an important role in acid base chemistry. It helps in the dissociation of acids and bases resulting in the formation of H+(aq) and OH (aq) ions respectively. Water itself undergoes dissociation process which is called self-dissociation of water.

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Water and Dissociation of Acids & Bases

A substance is an acid if it furnishes H+ ions in its aqueous solution and a base if it furnishes OH ions. Water plays very important role in these processes.

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