HPH102: Introduction and Electrostatics Miss L. G. Thwala

Real-time programming where actually you need knowledge about electronics which is very related to physics. Physics engine for graphical software. This is basically to know how stuff react when thrown, bumped into something else. May be knowledge about lenses and how light passes through: related to 3D rendering software ie computer engineering Hardware design eg information storage by Magneto-striction

INTRO What depends on physics around you? Would you say physics is the basis of the world??? physics is at the root of computers, television, radio, telecommunications, household lighting, and even the ability of food wrap to cling to a container.

THIS COURSE electrostatics, Electromagnetism circuit theory 2. Yes because study of electricity in this case is

every object contains a vast amount of electric charge Nucleus ~ 10-14 m Proton neutron Neutral atom every object contains a vast amount of electric charge  PARTICLE CHARGE (C) MASS (kg) Electron - 1.6 x 10-19 9.11 x 10-31 Proton +1.6 x 10-19 1.673 x 10-27 Neutron 1.675 x 10-27

How do Charged objects interact? Difference between electrostatic and gravitational force? What is your understanding of the law of charge? The coulomb (C) is the unit of electric charge. The basic quantity of electric charge (e) is 1.6 x 10-19 C.

- - - + Charge “Charged” particles exhibit forces Like charges repel each other + - Opposite charges attract one another Charge is the source of one of the fundamental forces in nature (others?)

Electrostatics: Applications The attraction and repulsion between charged bodies have many industrial applications. Thus static electricity has many practical uses for example: electrostatic paint spraying and powder coating, defibrillators, electrostatic dust precipitators fly-ash collection in chimneys, nonimpact ink-jet printing and

Electrostatic dust precipitators defibrillators

Electrostatics Appl: Photocopiers and laser printers In a photocopying machine, a carrier bead is covered with particles of black powder called toner, which stick to it by means of electrostatic forces. The negatively charged toner particles are eventually attracted from the carrier bead to a rotating drum, where a positively charged image of the document being copied has formed. A charged sheet of paper then attracts the toner from the drum itself, after which they are heat fused permanently in place to produce the copy.

Photocopy Machines and Computer Printers Use Electrostatics

Photocopy Machines and Computer Printers Use Electrostatics Laser printer is similar, except a computer controls the laser intensity to form the image on the drum

Electrostatics Appl: Photocopiers and laser printers…. A laser printer works in a similar way.

Electrostatics Appl: Paint Spraying Car manufacturers can save money by using charged paint spray guns. They work because like charges repel and unlike charges attract. The spray gun is charged positively, which causes every paint particle to become positively charged. Like charges repel and the paint particles spread out. The object to be painted is given a negative charge and so attracts the paint particles. The advantages of using this system are that less paint is wasted, the object receives an even coat and the paint covers awkward ‘shadow’ surfaces that the operator cannot see.

6-6. Conductors and Insulators A conductor is a substance through which electric charge flows readily. An insulator is a substance that strongly resists the flow of electric charge. Semiconductors are substances whose electrical conductivity is between that of conductors and insulators.

Semiconductors Transistors are switches that conduct electricity only when a second source of electricity is energized. What a Transistor looks like. A current will not flow from A to B unless C is energized.

Coulomb’s Law q1 q2 r (meters) (Newtons) F1,2 is the electrostatic force exerted on charge 1 due to the presence of charge 2 ke is the Coulomb constant ke = 8.987 x 109 N*m2*C-2

ELECTRIC FIELDS… The presence of an electric charge produces a force on all other charges present. Definition: The electric field E is the force exerted per unit charge, assuming the “test charge” is extremely small, so it doesn’t add its own field to the mix!

Visualizing Electric Fields: A Single Point-Charge The number of field lines starting (ending) on a positive (negative) charge is proportional to the magnitude of the charge. The electric field is stronger where the field lines are closer together.

Visualizing Electric Fields: Two Charges The lines emanating from two equal charges, opposite in sign will connect to form a Dipole (two poles). While if the charges are the same, the lines will avoid each other, and the charges repel

More Complex Field Lines and Symmetry The electric field between two closely spaced, oppositely charged parallel plates is constant. -where might this configuration occur?

Electric Fields and Conductors The static electric field inside a conductor is zero. The free charges “instantly” align themselves to totally cancel the external field. The net charge on a conductor is all on its surface. -Charges want to be as far apart as possible. Faraday Cage, Car in Thunderstorm etc…

Summary of Chapter 16 Two kinds of electric charge – positive and negative Charge is conserved Charge on electron: Conductors: electrons free to move Insulators: nonconductors

Summary of Chapter 16 Charge is quantized in units of e Objects can be charged by conduction or induction Coulomb’s law: Electric field is force per unit charge:

Summary of Chapter 16 Electric field of a point charge: Electric field can be represented by electric field lines Static electric field inside conductor is zero; surface field is perpendicular to surface

KNOWLEDGE IS POWER……. IGNORANCE IS DANGEROUS !!!!!!!!!!!!!!!!!! TO BE CONTINUED….