Elementary Electrostatics - PowerPoint PPT Presentation

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Elementary Electrostatics

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Title: PowerPoint Presentation Author: schaefer Last modified by: Maitreyee Baneerjee Created Date: 1/28/2003 8:39:32 PM Document presentation format – PowerPoint PPT presentation

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Title: Elementary Electrostatics


1
Elementary Electrostatics
  • Rubbing a balloon on a wool jumper makes the
    balloon attract your hair
  • The balloon is said to be charged or to have an
    electric charge
  • Similarly glass rubbed with silk/fur will become
    charged
  • Charged glass will attract a charged balloon
  • Two charged balloons will repel each other

2
Types and Sources of Electric Charge
Two kinds of electric charge positive
negative
protons
electrons
3
Electric Charge
  • All ordinary matter contains both positive and
    negative charge.
  • You do not usually notice the charge because most
    matter contains the exact same number of positive
    and negative charges.
  • An object is electrically neutral when it has
    equal amounts of both types of charge.

4
Properties of Electric Charge
  • Charge is quantized.
  • Positive and Negative charges have same
    magnitude
  • e p 1.6 x 10-19 C
  • SI unit of charge is the Coulomb
  • Charge is conserved.

5
Behaviour of Charges
  • Like charges repel
  • Unike or opposite charges attract
  • Q ne where n is a whole number

6
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7
Seeing the effects of charge the electroscope
  • the electroscope is a simple device for observing
    the presence of electric charge
  • it consists of a small piece of metal foil (gold
    if possible) suspended from a rod with a metal
    ball at its top
  • If a negatively charged rod is placed near the
    ball,
  • the electrons move away because of the
    repulsion.
  • The two sides of the metal foil then separate.

8
Atoms and Materials
Classification of Materials Conductors,
Insulators, Semiconductors
9
Different Methods of Charging
  • Friction e.g. rubbing a balloon with wool
  • Conduction e.g. touching an electroscope
  • Induction e.g. balloon sticking to a wall

10
How do we charge an object? Charging by rubbing
  • When two neutral objects are rubbed together,
    charge is transferred from one to the other and
    the objects become oppositely charged.
  • This is called charging by friction.
  • Objects charged by this method will attract each
    other.

11
How do we charge an object? Charging by rubbing
Conductors charge will distribute around the
surface to try until equilibrium is
achieved. - charge only resides on
surface, not inside.
12
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13
Charge by Cnduction (contact)
14
Charge by Induction (no contact)
15
How do we charge an object? B. Induction
Inducing a charge without touching.
Conductors
Charge is physically moved in/on the materials.
16
http//www.tutorvista.com/content/physics/physics-
iv/electric-charges/charging-induction-animation.p
hp
17
Induction (contd)
Insulators
18
Fields and forces
  • You can think of the field as the way forces are
    transmitted between objects.
  • Charge creates an electric field that creates
    forces on other charges.

19
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20
http//qbx6.ltu.edu/s_schneider/physlets/main/efie
ld.shtml
21
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22
Drawing the electric field
23
Lightning- outdoor spark
  • causes 80 million dollars in damage each year in
    the US
  • On average, kills 85 people a year in the US
  • over in a thousandth of a second
  • carries up to 200,000 A
  • causes the thunder!

24
development of a lightning bolt
stepped leader
leader streamer
leader meets streamer
lightning bolt
charge separation
25
applications of electrostatics
  • Xerox copiers use electrostatic attraction to put
    the ink droplets on the paper
  • electrostatic precipitators use the attraction of
    charged dust to remove dust particles from smoke.
  • can be used to hold balloons on your head

26
Removing soot particles
Positive cylinder
Chimney stack
Charging units spray electrons on the
soot particles
soot
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