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Lecture 2

# PCS 181 Lecture Notes - Lecture 2: 30 Foot Fall, Astronomical Unit, Bell Labs

Department
Physics
Course Code
PCS 181
Professor
Margaret Buckby
Lecture
2

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Ionation
Essay Topics: Virtual Particles, String Theory.
*Know the Hydrogen spectrum for Test # 1.
The Doppler Effect in Astronomy:
Star = Light Waves… take spectrum.
If the entire pattern of spectral lines is:
Shifted to the blue end of the spectrum (blue shifted) =
Shorter distance between wave crests =
Object is moving toward you.
If the pattern is:
Shifted to the red end of the spectrum (red shifted) =
Greater distance between wave crests =
Object is moving away from you.
Direction of Motion:
Take the Spectrum of a stationary (= NOT Moving) Source (e.g., hydrogen) in the
laboratory.
Take the Spectrum of a moving object (e.g., a Star).
Compare the two spectra’s.
Hydrogen Spectrum in Lab compared to Stellar Spectrum.
Two Blues, One Green, One Red = Know this Laboratory Spectrum.
Purple, Second Blue Line
Two Blues = Hydrogen Delta, Second Blue Line = 434 nm = Hydrogen Gamma, One
Green = Hydrogen Beta, One Red = Hydrogen Alpha.
*Test Question: Is the star moving toward you or away from you.
Doppler Effect to Determine Velocity:
Let C = Speed of Light = 3 x 108 m/s.
Triangle Delta = Wave length difference between lab and stellar (STAR) Spectra.
Delta lab = Wave length on lab Spectrum.
Vr = Radial Velocity of Star.
Then,
Vr = C Triangle Delta
Deltalab
Velocity of Star,
Vr = (3 x 108 m/s) = (434.1 434) nm
434nm