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class 10 Science cbse ncert notes

Chemical Reactions and Equations

The process in which a substance goes under chemical change and a new or more products are formed is called A CHEMICAL REACTION. In other words when two or more chemical substances combined together in certain condition; new product or products area formed.

Substances which go under chemical reaction are called reactants and resulted compounds are called products.

We encounter and witness many chemical reactions in our daily life. For example burning of coal, burning of gas, respiration, food making by green plants using photosynthesis, etc. and many more.

When we inhale air, oxygen present in air oxidized our blood and carbon dioxide comes out in this process. This reaction is the life line of living beings.

Without chemical reaction life is not possible.



Acid, Base & Salt

Many substances taste sour while many substances taste bitter on the other hand many substances taste sweet.

Substances that taste sour are called ACID and substances that taste bitter are and feel soapy in touch are called BASE. Base is known as Alkali also, but all bases are not categorized as alkali. Base with some special characteristics are called alkali.

According to modern definition, substances that dissociate hydrogen ion (H+) in aqueous solution are called ACID and substances that dissociate hydroxide ion (OH) in their aqueous solution are BASE.

Acid turns blue litmus paper red while base turns red litmus paper blue. Litmus is a natural indicator; turmeric is another such natural indicator. Since turmeric is a natural indicator, that is why when soap, which is basic in nature, rubbed on a stain of curry on a white cloth it becomes reddish–brown. And it becomes yellow again when the cloth is washed with plenty of water.



Metals & Non-metals

Substances can be categorized into two types, metals and non–metals.

Metals are shiny. This is the cause that silver and gold which are metals, used in making jewelry. Metals are good conductor of electricity and heat, this is the cause that electric wires are made of metals to conduct electricity and cooking utensils are also made of metal to conduct heat to cook food.

Metals produce ringing sound that is why our school bell is made of metal.

Metals are hard that is why iron which is a metal is used in making big structures, such as bridge, ships, etc.

Most of the metals are hard but some metals are soft, such as sodium which is a metal but can be cut using knife easily.

On the other hand non metals show about opposite properties to the metals. All gases are metal.

Regardless of properties both metals and non metals are useful to us and base of human life.

Iron is a metal and make our blood enable to carry oxygen, on the other hand oxygen is a non metal and enable us to live by oxidizing our blood.



Carbon and Its Compounds

At every step of life carbon is present. Every living being contain carbon. Carbon is life line of living beings. Carbon is one of the unique material on the earth.

Carbon dioxide is a gas and contains carbon as one of the components. We expels carbon dioxide in the course of respiration. Carbon dioxide is one of the important component of photosynthesis, the food making process of green plants, on which all living being depend.

Carbon is called tetravalent because valency of carbon is 4. This property makes carbon a unique element. Because of 4 valency carbon makes enormous number of compounds after combining with other elements. There are millions of carbon compounds known so far and many more are waiting to discover by us.

The earth crust has only 0.2% carbon in the form of minerals while the atmosphere has 0.3% of carbon dioxide. In spite of this small amount of carbon available in nature, the importance of carbon seems to be immense.



Periodic Classification of Elements

There are 118 elements are known to us so far and still many more are to be discovered.

Once only few elements are known to us and they could be arranged without any proper classification. But with increase of number of elements, it became necessary to classify them on their unique characteristics for the ease of their study.

Many attempts were made to classify the elements, but only Mendeleev a Russian scientist, got the credit first to classify them properly. The table prepared by Medeleev to classify the elements is known as "Mendeleev's Periodic Table of Elements".

Due some anomalies and problem in the classification of elements by Mendeleev, other scientist were keep trying continued to classify the elements.

With the effort of many scientists, Modern Periodic Table of Elements prepared to classify the elements correctly. The main credit goes to Henry Mosely to for the preparation of Modern Periodic Table.

Modern Periodic Law says that 'Properties of elements are periodic function of their atomic number.'



Reproduction

Reproduction is one of the main characteristics of living beings. Reproducing organisms create new individuals that look very much like themselves.

Reproduction at its most basic level will involve making copies of the blueprints of body design. A basic event in reproduction is the creation of a DNA copy.

Populations of organisms fill well defined places, or niches, in the ecosystem, using their ability to reproduce. The consistency of DNA copying during reproduction is importance of body design features that allow the organism to use that particular niche.

Reproduction is therefore linked to the stability of population of species.



Heredity and Evolution

The branch of science which deals with the transmission of characters from one generation to another is known as heredity and it can be defined as the science which deals with the inheritance of characters from one generation to next generation or from parents to offspring.

Variation is the differences in the trait among the organisms of a species. An offspring does not exactly resemble to either of its parents. It receives 50% of its characters from father and 50% from mother. Parents may differ in many characters like height, skin, color, eye color, types of hair, shape of nose, chin and so many other characters. All these differences are called variations.

These variations are also observed in animals and plants. The greatest advantage of variation in a species is that they increase the chances of survival in a changing environment.

Heredity is the transmission of characters from parents to their offsprings. Heredity is not similar in Asexual and Sexual Reproduction.



Light: Reflection & Refraction

It is the light which makes us enable to see the world. In the absence of light we cannot see any thing, such as in a dark room we are unable to see.

Light bounces back after falling on a surface similar to a rubber ball. The bouncing back of after falling on a surface reaches to our eyes and we can see that very object.

The bouncing back of light after falling on a reflecting surface is called Reflection of Light. In a mirror we can see our image because of reflection of light.

On the other hand speed of light changes when it enters from one medium to other medium, such as from air to water. The change in speed of light when travelling from different medium is the base of refraction.

Phenomenon of bending of ray of light towards normal while entering from rarer medium to denser medium and vice versa is called the Refraction of Light.

When light enters from rare medium, say air to a denser medium say water, it bends towards normal and when enters from denser medium to rarer medium, say from water to air, it goes away from normal. This phenomenon is called The Refraction of Light.



The Human Eye

Eye is one of the most important sense organs. It is the eye which enables us to see and understand the colourful world around us. There are many persons who cannot see and are called blind.

Eye works like a camera, rather camera was invented after observing the working pattern of eye and it can be said that camera works like an eye.

The structure of human eye is similar to a spherical ball. Light coming from object enters into eye ball through the lens and cast the inverted image at retina, which is a light sensitive screen located at the back portion of eye ball. Optic nerves send this image to the brain which interprets the correct picture and we see the object or anything.

The whole eye is generally called eye ball. Human Eye ball is approximately spherical in shape. It has a diameter of about 2.3 cm. There are several parts of eye ball.



Electricity

Today electricity became one of the most important needs for human. It appears that without electricity we cannot live.

Electricity is a type of energy that can be controlled and used to make our life comfort.

Flow of water through a water body, such as river, ocean etc. is called water current. Flow of wind is called wind current. Similar to that electric charge flows through a conductor and this flow of electric charge is called electrci current.

Substances which allow the flow of electric charge through them are called conductor. Metals are good conductor of electricity. This means metals allow flow of electric charge through them. That's why electric wires are made of metals.

According to some Egyptian Texts of about 2750 BC back, people were aware about electric current. People know about a type of fish which gave shock. Such fish were called 'THUNDER OF NILE' and were considered as protector of fish.

From ancient time it was known that when a rod of amber is rubbed with cat's fur, the rod of amber gets a capacity to attract smaller objects, such as hair, bits of paper, etc. Around 600 BC, Thales of Miletos concluded that friction makes amber magnetic, i.e. it becomes able to attract small objects.



Magnetic Effects of Electric Current

When a compass is brought near an electric current carrying conductor, the needle of compass gets deflected; this happens because of magnetic field produces by electric current. This phenomenon is called magnetic effect of electric current.

Magnet is a substance with a special property or capacity to attract iron and nickel or substances made of iron or nickel towards it. A magnet has two poles, i.e. North Pole and South Pole. When a magnet is suspended free using a thread, its one end points towards north direction and another end points towards south direction. End of magnet that points towards north direction is called North Pole or north seeking and end that points towards south direction is called South Pole or south seeking.

Electricity and Magnetism are related phenomenon. This was first observed by Hans Christian Oersted, a Danish scientist in 1820. In his honour the unit of magnetic field strength is named as Oersted.



Sources of Energy

Capacity of doing work is called energy. We use our muscular energy to do many works. Apart from that we use many natural sources of energy, for example burning of wax is used in candle to get light. Burning of diesel or petrol is used to run vehicles.

One form of energy can be converted into other form, for example to lit an electric torch we convert chemical energy into light energy.

There are many sources of energy we have, such as fossil fuels, wood, solar energy, wind energy, water energy, etc. which we use to make our life comfortable.

Many millions of years ago living organisms, such as trees and plants, got buried. Over the time period because of anaerobic decomposition dead organisms were converted into forms sources of energies. These sources of energy are called FOSSIL FUELS.

Coal, petroleum and natural gases are example of fossil fuels. Today human depends almost completely on these fossil fuels to get energy.