Lecture 39   iq34

Demo:  Generation of EM waves from a Tesla coil

Homework: Ch24.h3

1. Sinusoidal running waves:

o Wavelength, period, speed,

o  Spectrum of EM waves

2. Radiation: Energy density, intensity and time averaged intensity

o Equal partition between electric and magnetic energies

o Intensity vector (the Poynting vector)

o Intensity from a spherical wave  (h3:4) vs  from a 1D plane wave (h3: 1).

 3. Radiation pressure

o Relation between energy and momemtum – Relativistic kinematics

o Radiative force (magnetic force) on a charge is along the direction of motion and is independent of sign of the charge. (h3:14)

o Pressure on an absorptive (black) surface vs reflective surface (h3:3, 10-12)

4. Polarization of the radiative waves

o Parallel metal strips  allows the passage of perpendicularly polarized light. Polarizer has  the transmission axis perpendicular to the strip.

o A polarized light through a polarizer. Malius’ law

o Unpolarized light through two polarizers. LM MI-Ch24 6-7. 001-002

5. Rescattered sunlight in the sky (h3: 7-8)

o It is polarized.

o Its intensity (I=cu=c eps E^2) depends on the inverse fourth power of the wavelength.  (why?)

Class announcement:

o The updated course summary of unit 4 has been posted with the date 4/21/13.

o Since LM covered Malus Law, we have added it in the summary page.

o We have left out h5 in our updated lesson plan, the corresponding course-material on lens has been removed from the summary.  

o Office hour today will be postponed by 15 minutes. It will be from 9:30am to 10:30am.

o Application of the LA position is now available. For those of you who do well in this course are encouraged to apply. LAs are playing an important part in helping students through their interaction with students. If you are interested in this job opportunity please contact Lisa Gentry*.

*Lisa’s contact information: Undergraduate Coordinator, Department of Physics

Ph: 512-471-8856  Fax: 512-471-9637

email address: ugaffairs@physics.utexas.edu