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

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

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.

The Last LectureCovering 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

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

Almost Maxwell

Bindell

Gauss

Faraday

Ampere

EB Together

Problem

Remember the Lowly Capacitor?

AC CurrentI

But there MUST be a magnetic field present

around the gap - even if it is small!

- 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

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

MAXWELLS EQUATIONS

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.

Sorry its crooked!

Propagation Direction

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.

EnterHeinrich 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

Hertz Experiment

So far we can assume

Extended View Sine Shape

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

The Velocity is c

- This must describe light waves ..

It can be shown that the wave carries energy and

momentum,

Receiver!

How??

FINAL DEMO!