2 ElectrostaticsAncient Greeks were familiar with electrostatic phenomenon.A piece of amber rubbed with fur could attract small objects over a distance.
3 ThinkWhat is another force that acts over a distance?
4 Electric Nature of Matter Atoms are made of protons and electrons.Electrons (negative charge) are free to move, while protons (positive charge) are not as free to move.Matter usually has a balanced charge.
6 Static Electricity: Definition An imbalance of charge.Usually it is the electrons that move.
7 Mechanisms of Charge Imbalance Contact/Peeling:Rub balloon on hair.Conduction:Touch a charged object to a neutral object.Induction:Bring a charged object close to a neutral object.positivenegativeneutral
8 Van de Graff GeneratorLike amber and fur, a rubber belt transfers charge from a wool roller to the dome.The charge builds up and is distributed on the surface of the sphere.
9 Electrostatic ForcesLike charges repel.Unlike charges attract.We have seen that electric charges exert forces on other electric charges.
10 Think-Partner-ShareWhat factors might affect the magnitude of this electrostatic force?
11 Electrostatic Forces F = Kq1q2 r2 Coulombs Law Like charges repel. Unlike charges attract.Coulombs LawF = Kq1q2r2
12 Coulomb’s Law: force between two charged particles F = Kq1q2r2K = 9 x 109 Nm2/C2 (electrostatic constant)q = value of charge in CoulombsA comb has a charge of about 1 microcoulomb (10-6 C)r = distance between charges.Note the inverse square relationship.
13 ThinkWhat is another inverse square relationships we have seen?
14 Electric Field"An electric field is a region in which charged particles experience a force"ELECTRIC FIELD+qFORCEFORCE-qLines of force show the direction of the force felt by a positive charge
15 Field Lines - Field Lines start and end on charges. +Field Lines start and end on charges.The density of field lines is a measure of the strength of the field.
16 ELECTRIC FIELD STRENGTH E +qIT IS A VECTORELECTRIC FIELD STRENGTH EThis is defined as the force per unit charge acting at a point in the field. UNITS =N/CHence the force on a charge of q coulombs in the diagram above is given by :F = E q
17 Motion of Charge Initially Moving Perpendicularly to an Electric Field e.g. an electron in an oscilloscope beam.yExvH--VH is the initial horizontal velocity and REMAINS CONSTANT - Like a projectile !!For the vertical motion u = 0, sowhere m = mass of the particle and F = EqFor the horizontal motion, x = VH twhich is a PARABOLAHence
18 What is electricity?The interaction between charged particles of matter.We discussed “static” electricity or charge imbalance – how about if charges are moving?
19 Current ElectricityCurrent = flow of charge, such as electrons through a wire in a circuit.