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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
• 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
• 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
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,