Daily phenomena Basic Definitions 1 Electrostatics Next Slide Daily phenomena “Charge” plastic materials by friction Experience of electric force and electric charge Repulsive and attractive electric force Different kinds of charge : positive (+) and negative (-) General Rule : like charges repel; unlike charges attract

Nature of charges Basic Definitions 2 Electrostatics Next Slide Nature of charges Structure of atoms and matter Diagram Balance of charge : no. of electrons = no. of protons Neutral : no. of electrons = no. of protons Diagram Positively charged : no. of electrons < no. of protons Negatively charged : no. of electrons > no. of protons Charging by changing the no. of electrons only

Nature of charges Basic Definitions 3 Electrostatics Next Slide Nature of charges Unit : Coulomb (C) Insulators (like plastics) : do not allow electrons to flow through them or escape easily Conductors (like metals) : allow electrons to flow through them or escape easily Charging by friction Diagram Induced charge Diagram

Different ways of charging Electrostatics Next Slide Different ways of charging Charging by extra high tension power (EHT) supply Photo Charging by Van de Graaff generator Photo Charging by sharing Diagram Charging by induction and separation Diagram Charging by induction and earthing process Diagram

Nature of electric field Electrostatics Next Slide Nature of electric field Presence of electric field : experience of electric force by a small charge around a charged object Representation of electric field : field lines Electric field pattern around a positive charge Diagram Electric field pattern around a negative charge Diagram Various electric field patterns Diagram Experimental setup to demonstrate electric fields Photo

Application of charges Applications 1 Electrostatics Next Slide Application of charges Action of a point Diagram Lightning conductor and action of a point Diagram Electrostatic precipitation Photocopying

Electrostatic hazards Applications 2 Electrostatics Next Slide Electrostatic hazards Sheets of paper stick together in industry Wool, cotton and artificial fibres attract dust Sparks produced in vehicles and planes

END of Electrostatics

Back to Basic Definitions 2 Electrostatics Click Back to Matter is made up of tiny particles called atoms Model of an atom : nucleus electron : negative (-) charge proton : positive (+) charge neutron : no charge A proton has a positive charge and an electron has an equal negative charge while a neutron is uncharged

Back to Basic Definitions 2 Electrostatics Click Back to Assume that we have a rod which is made of 10000 atoms and each atom contains 2 protons, 2 neutrons and 2 electrons Electrically neutral (normal case) protons neutrons electrons 20000 Positively charged protons neutrons electrons 20000 18000 Negatively charged protons neutrons electrons 20000 23000

Back to Basic Definitions 3 Electrostatics Click Back to When a plastic rod is rubbed with a dry cloth, we have either one of the following cases. flow of electrons flow of electrons Plastic rod : +ve charged Cloth : -ve charged Plastic rod : -ve charged Cloth : +ve charged

Back to Basic Definitions 3 Electrostatics Click Back to A charged (either +ve or -ve) rod can attract a piece of aluminium foil which is neutral initially. flow of electrons Aluminium flow Since the electrons are attracted towards the upper end, the upper part becomes -ve while the lower part becomes +ve. large attractive force Since smaller separation means larger force, the attractive force is always larger than the repulsive force. small repulsive force

Back to Ways of charging Electrostatics Click Back to Extra high tension (EHT) power supply

Back to Ways of charging Electrostatics Click Back to Van de Graaff generator

Ways of charging Electrostatics Next Slide Consider two metal spheres which are supported by insulating stands as shown. One of the sphere is negatively charged while the other one is uncharged. Insulating stands Negatively charged sphere Uncharged sphere

Ways of charging Electrostatics Next Slide They are brought into contact with each other. Some of the electrons flow from the charged sphere to uncharged sphere. flow of electrons Both objects are then negatively charged.

Back to Ways of charging Electrostatics Click Back to Both spheres are then separated and negatively charged. This is called charging by sharing.

Ways of charging Electrostatics Next Slide Consider two metal spheres which are supported by insulating stands as shown. Both spheres are neutral and they are in contact with each other as shown. Insulating stands Uncharged spheres

Ways of charging Electrostatics Next Slide A positively charged rod is brought near one of the sphere. Induced charge appears as electrons flow from one sphere to another. Insulating stands flow of electrons

Ways of charging Electrostatics Next Slide The spheres are separated without removing the rod. Insulating stands

Back to Ways of charging Electrostatics Click Back to Then we remove the rod. One sphere is negatively charged while the other one is equally positive charged. No loss of charge from the charged rod This is the method of charging by induction and separation. Insulating stands

Ways of charging Electrostatics Next Slide We have a uncharged conducting sphere supported by insulating stand. A positively charged rod is brought near the sphere. Induced charge appears in the sphere. Insulating stands flow of electrons

Ways of charging Electrostatics Next Slide Touch the sphere with your finger or collect the sphere to the earth with a conducting wire without removing the rod. Electrons flow from the earth to the sphere and neutralize the +ve charge on the other side in the sphere. Insulating stands flow of electrons earthing process

Ways of charging Electrostatics Next Slide Remove the finger or the wire without removing the rod. Insulating stands

Back to Ways of charging Electrostatics Click Back to Remove the rod and we get a negatively charged sphere. No loss of charge in the rod is involved. This is the method of charging by induction and earthing process. Insulating stands

Back to Electric field Electrostatics Click Back to The electric field pattern around a positive charge is shown. The arrows and the lines represent the direction of force acting on a very small testing charge placed at that point.

Back to Electric field Electrostatics Click Back to The electric field pattern around a negative charge is shown. The arrows and the lines represent the direction of force acting on a very small testing charge placed at that point.

Electric field Electrostatics Next Slide Various patterns are shown in the following figures:

Electric field Electrostatics Next Slide

Electric field Electrostatics Next Slide

Back to Electric field Electrostatics Click Back to

Applications 1 Electrostatics Next Slide Action of a point : The charge has a tendency to concentrate on the sharp points of a conductor. Around these points, the electric field is so strong that the air molecules are ionized.

Back to Applications 1 Electrostatics Click Back to Let’s take a negatively charged object with a sharp end as an example. Positive ions are attracted towards the point while negative ions are repelled. Positive ions remove some electrons from the object and become neutral again. The charge on the object is reduced. The negative ions are repelled and move away from the point. The stream of ion flow is called electric wind. electric wind

Back to Applications 1 Electrostatics Click Back to Lightning conductor is a metal rod with sharp ends and installed as shown in the following figure. electric wind Lightning conductor provides a route for electrons (lightning) to pass into the ground. Electric wind reduces the charge on the cloud and the induced charge on the roof.