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Chapter 1, Electric Charges and Fields, Electrostatics, Electrostatics deals with the study of forces, fields and potentials, arising from static charges., Frictional electricity, The electricity produced by rubbing suitable bodies is called frictional, electricity., On rubbing electrons are transferred from one body to the other. The, body, which loses electrons, will become positively charged and which gains, electrons becomes negatively charged., Electric Charge, From simple experiments on frictional electricity, it is inferred that, there are two types of charges in nature-Positive and Negative ., Like charges repel and unlike charges attract., • When a glass rod is rubbed with silk, glass rod becomes positively charged, and silk negative., • When a plastic rod is rubbed with fur, plastic rod becomes negatively, charged and fur positive., 1. Good conductors like copper cannot be charged by friction because any, charge produced on it can easily flow through the rod through our body and, to the ground., 2. Insulators like plastic, ebonite, glass etc can be easily charged by friction, because the charges will stay on them., 3. Electrostatic experiments cannot be performed in moist climate because, moist air is slightly conducting. So the static charges will get conducted, away from the charged body., , How is frictional electrification caused?, The number of protons inside the nucleus of an atom is equal to the, number of electrons outside the nucleus. When a body is rubbed with, another, due to friction, some electrons from one body get transferred to the, other body. The body, which loses electrons, will become positively charged, and which gains electrons becomes negatively charged. The two bodies thus, acquire opposite charges and they are equal in magnitude. This is the, reason for frictional electricity.
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Gold Leaf Electroscope, A simple apparatus to detect charge on a body is called a gold-leaf, electroscope., Apparatus: It consists of a vertical metal rod placed in a box. Two thin gold, leaves are attached to its bottom end as shown in figure., , Working: When a charged object touches the metal knob at the top of the, rod, charge flows on to the leaves and they diverge. The degree of divergence, is an indicator of the amount of charge., Conductors and Insulators, Conductors, Conductors are those substances which allow passage of electricity through, them., Eg. Metals, human and animal bodies and earth are conductors., • They have electric charges (electrons) that are comparatively free to move, inside the material., • When some charge is transferred to a conductor, it readily gets, distributed over the entire surface of the conductor., • Metals cannot be charged by friction, because the charges transferred to, the metal leak through our body to the ground as both are conductors of, electricity., Insulators, The substances which offer high resistance to the passage of electricity, through them are called Insulators., Eg. Glass, porcelain, plastic, nylon, wood, • If some charge is put on an insulator, it stays at the same place. So, insulators gets electrified on combing dry hair or on rubbing,, Earthing (or) Grounding, When a charged body is brought in contact with earth, all the excess charge, pass to the earth through the connecting conductor. This process of sharing, the charges with the earth is called grounding or earthing. Earthing, provides protection to electrical circuits and appliances.
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Methods of Charging: A body can be charged in different ways, 1) Charging by friction, 2) Charging by conduction, 3) Charging by induction, 1) Charging by friction, When two bodies are rubbed each other, electrons in one body (in, which electrons are held less tightly) transferred to second body (in which, electrons are held more tightly), When a glass rod is rubbed with silk, some of the electrons from the, glass are transferred to silk. Hence glass rod gets +ve charge and silk gets ve charge., 2) Charging by conduction, Charging a body with actual contact of another body is called charging by, conduction. If a neutral conducting body (A) is brought in contact with, positively charged conducting body (B), the neutral body gets positively, charged., 3) Charging by induction, When a charged body is brought near to an uncharged conductor, (without touching), that end of the uncharged conductor which is near to, the charged body gets oppositely charged and the farther end is charged, with the same type of charge., , Charging a metal sphere positively without touching it, , Bring a negatively charged rod near an earthed conductor fig(b).Positively, charge is produced near the rod and negative charge flows to earth. Fig(c)., when the charged rod is removed the positive charge get uniformly, distributed over the surface and we get a positively charged conductor
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