Monday, March 3, 2008
Announcements:
Assignments:
- Read Chapter 10 and be prepared to discuss on Wednesday.
- Answer the recommended conceptual exercises and problems for
Chapter 10, and check your understanding by
looking at the answers in the back of the textbook.
- Submit your topic ideas for the physics Web Project.
Chapter 9 - Electromagnetic radiation
Electromagnetic waves consist
of oscillating
electric and magnetic
fields that are at right angles to each other and in phase.
EM waves travel at the speed of light,
which in a vacuum is exactly (by
definition): c = 299 792 458 m/s
This is fast by human time and
length scales, but slow on astronomical scales (see chart).
The electromagnetic spectrum
is divided into "bands"
of frequency with
special names that relate to the corresponding energy.
Diagram
of EM spectrum with corresponding length scales and atmospheric
opacity. Another spectrum diagram.
Diagram
with ionization potential of radiation.
While the speed of light is the same for all EM
waves in a vacuum, the
energy of these waves depends on the frequency: E = hf
As was the case for other waves, the wave speed is
related to the
frequency and wavelength by: c = f*lambda
Radar = Radio Detection and Ranging, uses radio (EM)
waves
The importance of Maxwell's Equations is stated on a clever T-shirt
that says:
And God said:
∇ • E = ρ / εo
∇ • B = 0
∇ x E = - ∂B/∂t
∇ x B = μoJ + μoεo∂E/∂t
Translation: "Let there be light"
Demo: Resonance bars.
Leslie cube and IR thermometer
CFC effect on ozone depletion.
Global warming: Video clip from An
Inconvenient Truth (Chapters 8-9)
Greenhouse gas
|
Contribution
|
Main sources
|
carbon dioxide
|
49%
|
burning wood and fossil fuels,
plant and animal respiration, deforestation
|
methane
|
18%
|
wetlands, swamps, cattle, rice
paddies, forest and savanna burning, natural gas, landfills, termites,
oceans, lakes, and tundra
|
chlorofluorocarbons
|
14%
|
refrigerants, solvents, foamed
plastic
|
nitrous oxide
|
6%
|
auto exhaust, fertilizers
|
Source: http://www.enviroliteracy.org/pdf/labge1.pdf
Greenhouse
gas absorption spectra.
CO2 absorption and
re-radiation. What errors can you find in this webpage?