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## Module 3 ### Wires, Joints - Soldering - U.G. Cables ### Introduction Electricity in motion is called electric current. Whereas the electricity that does not move is called static electricity. The examples of static electricity is shock received from door knobs of a carpeted room and attraction...

## Module 3 ### Wires, Joints - Soldering - U.G. Cables ### Introduction Electricity in motion is called electric current. Whereas the electricity that does not move is called static electricity. The examples of static electricity is shock received from door knobs of a carpeted room and attraction of tiny paper bits to the comb. ### Structure of matter Matter is defined as anything that has mass and occupies space. A matter is made of tiny, invisible particles called molecules. A molecule is the smallest particle of a substance that has the properties of the substance. Each molecule can be divided into simpler parts by chemical means. The simplest parts of a molecule are called atoms. ### Atomic structure An atom contains three types of sub-atomic particles that are of relevance to electricity. They are the electrons, protons and neutrons. The protons and neutrons are located in the centre, or nucleus, of the atom, and the electrons travel around the nucleus in orbits. - **The Nucleus:** The nucleus is the central part of the atom. It contains the protons and neutrons in equal numbers. - **Protons:** The proton has a positive electrical charge. It is almost 1840 times heavier than the electron - **Electron:** It is a small particle revolving round the nucleus of an atom. It has a negative electric charge. The electron is three times larger in diameter than the proton. In an atom the number of protons is equal to the number of electrons. - **Neutron:** A neutron is actually a particle by itself, and is electrically neutral. ### Energy shells In an atom, electrons are arranged in shells around the nucleus. A shell is an orbiting layer or energy level of one or more electrons. The major shell layers are identified by numbers or by letters starting with 'K' nearest the nucleus and continuing alphabetically outwards. There is a maximum number of electrons that can be contained in each shell. **For example, a copper atom which has 29 electrons would have four shells with a number of electrons in each shell as shown in figure** - **K shell** complete (2) - **L shell** complete (8) - **M shell** complete (18) - **N shell** incomplete (1) ### Conductors A conductor is a material that has many valance electrons permitting electrons to move through it easily. Generally, conductors have one, two or three electrons in their shells. Most metals are conductors. Some common good conductors are Copper, Aluminium, Zinc, Lead, Tin, Eureka, Nichrome, etc. Silver and gold are very good conductors. ### Insulators An insulator is a material that has few, if any, free electrons and resists the flow of electrons. Generally, insulators have five, six or seven electrons in their shells. Some common insulators are air, glass, rubber, plastic, paper, porcelain, PVC, fibre, mica etc. ### Semiconductors A semiconductor is a material that has some of the characteristics of both the conductor and insulator. Semiconductors have valence shells containing four electrons. Common examples of pure semiconductor materials are silicon and germanium.