Electricity%20and%20Magnetism - PowerPoint PPT Presentation

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Electricity%20and%20Magnetism

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In E&M, we will deal with forces that depend upon charge ... Franklin's Kite. He flew a kite in a thunderstorm and saw that charge flowed down the string ... – PowerPoint PPT presentation

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Title: Electricity%20and%20Magnetism


1
Electricity and Magnetism
  • Physics 102
  • Professor Lee Carkner
  • Lecture 9

2
Electricity and Magnetism
  • In EM, we will deal with forces that depend upon
    charge
  • Stationary charges exert an electric force
  • EM forces only affect charged particles

3
Forces
  • The electric force is much stronger than the
    gravitational force
  • Why dont we feel this strong force?
  • Most things have roughly equal numbers of
    positive and negative particles
  • Like charges repel, opposite attract
  • e.g. lightning, static electric shock

4
Plus and Minus
  • The basic particle of positive charge is the
    proton
  • Protons generally dont move
  • Electrons are in the shells of atoms and can be
    removed
  • Adding electrons makes something negative
  • All EM forces depend on what the electrons are
    doing

5
Using Electricity
  • Why is the electrical force important?
  • Convert electrical energy into work
  • Convert electrical energy into heat and light
  • Convert electrical energy into sound
  • Electrical energy can be very finely controlled

6
Making Electricity
  • Three ways to do this
  • Chemically
  • Magnetically
  • Physically
  • Four basic methods friction, conduction,
    induction, polarization

7
Triboelectricity
  • Rubbing will transfer electrons from one
    substance to the other by friction
  • Example Glass rubbed with silk becomes positive,
    rubber rubbed with fur becomes negative

8
How Does Charge Move?
  • Some types of material allow electrons to move
    freely (e.g. metals)
  • When you charge a conductor, the electrons will
    flow through it
  • Other types do not allow electrons to flow (e.g.
    glass, rubber)
  • If you charge them, the charge stays put

9
Conduction
  • Both end up with the same sign charge
  • Example shocking your friend

10
Induction
  • Said to be grounded
  • If you place a charged object near a grounded
    conductor it will repel the same sign charges to
    the ground
  • Charge is opposite that of the inductor

11
Polarization
  • You have charged the balloon but not the wall
  • The negative charge on the balloon attracts the
    positive charged parts of the molecules of the
    wall, polarizing it

12
Polarization
13
Origins of Electricity
  • Moving charges by rubbing has been known since
    ancient times
  • Benjamin Franklin proposed the terms positive and
    negative for the two types of charge

14
Franklins Kite
  • He flew a kite in a thunderstorm and saw that
    charge flowed down the string

15
Next Time
  • Read 16.5-16.7
  • Also read 16.1-16.4 for today
  • Schedule for next few weeks now up on class web
    page
  • Homework Ch 16 P 1, 5, 23, 24
  • See me if you have concerns about your exam
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