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Electromagnetic waves

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Electromagnetic waves Bringing It All Together This Week Today- No Clickers sell them back to the bookstore unless you are planning to take my section of the ... – PowerPoint PPT presentation

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Title: Electromagnetic waves


1
Electromagnetic waves
  • Bringing It All Together

2
This Week
  • Today-
  • No Clickers sell them back to the bookstore
    unless you are planning to take my section of the
    course next semester. Bad idea!
  • We tie the stuff together and do the candle trick
    right in front of you. (Remember the video??)
  • The rest of the week FINAL EXAMS

3
My schedule
  • Tuesday Not on Campus
  • Wednesday Friday
  • Giving exams
  • Grading Papers
  • In foul mood! Stop by if you need to.
  • Grades will be completed as fast as I can.
  • Grader has finals this week to, so it may be a
    slow process.

4
The Last Lecture Covering 5 Additional Chapters
  • We have been looking at the properties of
    Electric Fields.
  • We have been looking at the properties of
    Magnetic Fields
  • We looked at a few situations where there was
    some kind of connection between the two.
  • We saw that ALL of what we discussed could be
    explained by one set of equations.
  • MAXWELLs Equations

5
James Clerk Maxwell
  • 1831 1879
  • Scottish physicist
  • Provided a mathematical theory that showed a
    close relationship between all electric and
    magnetic phenomena
  • His equations predict the existence of
    electromagnetic waves that propagate through space

SMART DUDE
6
Almost Maxwell
Bindell
Gauss
Faraday
Ampere
EB Together
Problem
7
Remember the Lowly Capacitor?
AC CurrentI
But there MUST be a magnetic field present
around the gap - even if it is small!
8
  • Ampères Law is used to analyze magnetic fields
    created by currents
  • But this form is valid only if any electric
    fields present are constant in time
  • Maxwell modified the equation to include
    time-varying electric fields
  • Maxwells modification was to add a term

9
Maxwell Fixed the Problem!
  • The additional term included a factor called the
    displacement current, Id
  • This term was then added to Ampères Law
  • Now sometimes called Ampère-Maxwell Law
  • This showed that magnetic fields are produced
    both by conduction currents and by time-varying
    electric fields

10
MAXWELLS EQUATIONS
11
Vacuum
  • There aint nuttin there.
  • No Charges
  • No Currents
  • Can there be electric or magnetic fields
    present??
  • Maxwells equations say YES
  • And they add some serious requirements to what is
    there.

12
Sorry its crooked!
13
Propagation Direction
14
Back to Maxwell
  • E M fields can propagate from a region where
    there are charges/currents to regions far away
    where they do not contain these sources.
  • The fields propagate as WAVES
  • Shape moves at the speed of the wave.
  • Because the E field is changing (moving charge
    example), there will be a B field there as well.

15
Enter Heinrich Rudolf Hertz
  • 1857 1894
  • German physicist
  • First to generate and detect electromagnetic
    waves in a laboratory setting
  • The most important discoveries were in 1887
  • He also showed other wave aspects of light

16
Hertz Experiment
17
So far we can assume
18
Extended View Sine Shape
19
The Magic From Ms 4
  • Mathematically these equations describe waves
    traveling thought space.
  • E and B are perpendicular to each other and to
    the direction of propagation.
  • The velocity of the wave must be

20
The Velocity is c
  • This must describe light waves ..

21
It can be shown that the wave carries energy and
momentum,
Receiver!
22
How??
23
FINAL DEMO!
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