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A body which has a definite weight and which occupies some space is called ‘Matter’. It is found in 3 states: solid, liquid & gas. Matter is made up of tiny particles.
Matter can be divided into tiny particles. The smallest particle of a matter which contains all the physical & chemical properties of the matter is called molecule.
The smallest particle of a matter which can take part in a chemical reaction but cannot exist freely is called an atom. The Atom is consisting of electrons, protons and neutrons. In an atom, a nucleus surrounded by electrons.
In an atom the total number of negatively charged electrons circling around the nucleus exactly equals the number of extra positive charges in the nucleus. The positive charges are called protons. Besides the protons, the nucleus also contains electrical neutral particles called neutron. These are like a proton & an electron bonded together.
Atoms of different elements contain different number of neutrons within the nucleus, but the number of electrons spinning about the nucleus. Always equals the number of free protons (or positive charges) within the nucleus. Electrons in the outer orbits of an atom are attracted to the nucleus by comparatively less force than electrons whose orbits are near the nucleus. These outer electrons are called ‘Free electrons’ and may be easily forced from their orbits, while electrons in the inner orbits are called ‘bound’ electrons. Since they cannot be forced out of their orbits easily. It is the motion of the free electrons that makes up an electric current.
The nucleus is the central part of the atom. It contains the protons and neutrons of an atom. The number of protons & neutrons in the nucleus varies. For the different elements depends on the particular atom involved.
The proton has a positive electrical charge. It is almost 1840 times heavier than the electron & it is the permanent part of the nucleus. Protons do not take an active part in the flow or transfer of electrical energy. Protons repeal each other but have a force of attraction for the negative electron.
It is a small particle revolving around the nucleus in an atom. The electron is three times larger in diameter than the protons. Protons = no. of electron, due to its orbital speed, around the nucleus, carrying a considerable amount of energy. Since all electrons are negative in charge, they will repeal other electron & have a force of attraction for the positively charged protons.
A neutron is actually a particle by itself and it is generally thought of as an electron & proton combined. It is electrically neutral. Since neutrons are electrically neutral, they are not important to the electrical nature of atoms.
The effect of electrons is moving from point to point in a material is called electricity.
The excess of electrons in one material is known as a negative charge.
The absence of electrons in the other material is called positive charge.
The flow of electrons in one direction, negative to positive is called Current. Its symbol is ‘I’ & it’s unit is ‘ampere’, symbol is ‘A’. Ammeter is used for measuring current. It is connected in series with load & supply. Electron theory current flow & conventional current flow. According to the electron theory, current flow is always from a negative charge (–) to a positive charge (+). Before the electron, theory of matter was discovered, this concept of current flow is called conventional current flow. For your study of electricity, current flow is concluded to be the same as convential current i.e. Current flows from positive terminal of the source to the negative terminal of source through the load.
One ampere of current is said to flow through a conductor when one coulomb of charge flows per second of charge flows per second across a cross-section of the conductor. (1 ampere = 1 coulomb / 1 second)
When the current flows, the electrical energy of the charges is utilized to move electrons/ charges from positive to negative terminals. This electrical energy is called electromotive force. Symbol is e.m.f. The unit of e.m.f. is volts & its symbol is ‘V’. In other words when electrons/ charges move from one terminal to another terminal as current flows the moving force is Electromotive force. Voltmeter is used for measuring e.m.f.
The difference in the electric potentials of two charged substances is called Potential Difference. Its unit is ‘Volt’ & symbol is ‘V’.
A potential of 1 Volt at a point means that 1 Joule of work is done in bringing a positive charge of 1 coulomb from infinity to that point. 1Volt = 1 Joule/ 1 second.
The opposition to current flow is not the same for all material. Current flow itself is the movement of ‘free’ electrons in a material determines its opposition to current flow. Atoms of some materials give up their outer electrons easily & such materials offer little opposition to current flow, while other materials hold on to their outer electrons & such materials offer considerable opposition to current flow. Every material has some opposition to current flow, whether large or small & this opposition is called resistance. OR The property of a substance which opposes the flow of current through it is called resistance. Its symbol is ‘R’. The unit of resistance is ‘ohm’ & its symbol is W Unit Ohm One ohm is defined as resistance of that conductor which allows a passage or a current of one ampere through it when a potential difference of one volt is maintained across its ends.
Intext Questions 4.1
a) Fill in the blanks:
1. A body which has definite weight & which occupies some space is called .
2. Smallest particle of a matter is known as .
3. Electrons consist of charge.
4. The flow of electrons in one direction is called .
5. Unit of current is .
b) State True or False:
1. Protons consist of negative charge. ( )
2. Ammeter is connected in parallel. ( )
3. The unit of EMF is Volt. ( )
4. Opposition to the current is known as resistance. ( )
5. Ohm is unit of resistance. ( )
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