Thursday, March 20, 2008

Gave students 30 minutes to finish up their "Save Jack" Labs.

Handed back RA 18.1, RA 18.2
Went over work sheets

Showed examples of superposition. Propagate waves than just algebraically add up the waveforms.

Electromagnetic spectrum: Radio waves, microwaves, infrared, Visible (R-O-Y-G-B-I-V), Ultraviolet, X-rays, gamma rays. Used v = wavelength * freq to calculate the wavelengths of AM and FM radio waves. Wavelength of microwave from microwave oven.
Used Wien's Law to calculate wavelength emitted by our bodies (infrared). Red wavelengths ~700 nm. Violet ~ 400 nm.

Demo that TV emits radio waves that we can pick up on radio set to static AM.
Discussed how microwaves cook food - resonant frequency with water molecules.
Showed how remotes, which emit IR, can be detected using a photocell and speaker, or by cell phone camera.

Standing waves: String fixed at both ends. v = sqrt(tension/(mass/length)).
Drew patterns of fundamental (first harmonic), and second and third harmonics for string, open pipe, and pipe open at one end and closed at the other. Derived general formulas for frequency for the various harmonics.

Used water filled pipe to find resonances.

Handed out worksheets on superposition and standing waves.