2ElectrostaticsAncient Greeks were familiar with electrostatic phenomenon.A piece of amber rubbed with fur could attract small objects over a distance.
3ThinkWhat is another force that acts over a distance?
4Electric 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.
6Static Electricity: Definition An imbalance of charge.Usually it is the electrons that move.
7Mechanisms 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
8Van 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.
9Electrostatic ForcesLike charges repel.Unlike charges attract.We have seen that electric charges exert forces on other electric charges.
10Think-Partner-ShareWhat factors might affect the magnitude of this electrostatic force?
11Electrostatic Forces F = Kq1q2 r2 Coulombs Law Like charges repel. Unlike charges attract.Coulombs LawF = Kq1q2r2
12Coulomb’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.
13ThinkWhat is another inverse square relationships we have seen?
14Electric 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
15Field 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.
16ELECTRIC 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
17Motion 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
18What is electricity?The interaction between charged particles of matter.We discussed “static” electricity or charge imbalance – how about if charges are moving?
19Current ElectricityCurrent = flow of charge, such as electrons through a wire in a circuit.