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Midterm

Notes before First Midterm (Units 1-3)

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Department
Physics
Course
PCS 181
Professor
Margaret Buckby
Semester
Fall

Description
PCS181 The Scientific Method Sept6/11 1. Observation 4. Conclusion 2. Hypothesis 5. Reproducibility 3. Experiment & is falsifiablecan be proven wrong & replaced with better theory Unit 1: The Electromagnetic Spectrum - Astronomical information is transmitted by starlight - Starlight: the stars temperature, chemical composition, motion, pressure, distance, magnetic fields & etc 8 - Light: mutually perpendicular oscillating electric & magnetic fields; moves in wavelike pattern at a speed of c = 3 x 10 m/s [lower case c = speed of light] - Wavelength, : distance between peaks of wave - Tachyons: theoretical faster-than-light particles Electromagnetic Properties slide 9 - Wavelength colour -9 -9 9 9 - 1 nanometer = 1nm = 1 m = 1 x 10 m = 10 m ; 10 = billionth 1 x 10 - red= 700 nm = 700 x 10 m = 7 x 10 m -7 -9 -7 - violet400 nm = 400 x 10 m = 4 x 10 m - yellowy-green50 nm = 550 x 10 m = 7 x 10 m -7 - Visible Colours: ROY G BIV - Photons: bundles of energy light as a particle - Fig5-3 (prism of light) - Gamma rays (nuclear) X-rays (deform) Ultraviolet (blind) Infrared (heat) Radio waves Frequency (how often happen during certain time period) 13 - Frequency = f = number of wave peaks passing a given point each second = number of waves/second = complete cycles/second = cycles/s = Hz - F = c/ = speed of light / wavelength 8 -9 14 14 - Fred = c = 3 x 10 m/s / 700 x 10 m = 4.3 x 10 cycles/s = 4.3 x 10 Hz - F violetc = 3 x 10 m/s / 400 x 10 m =??? Planck (blackbody) Curve - Get star in telescope, star light goes through prism - Sequence of coloured filters at eyepiece at end of telescope - blackbody absorbs all wavelengths - Planck Curve: graph of filter colour (= wavelength) versus intensity Calculate temperature of object via WIEN Formula: PCS181 o T = 0.0029 mK / dominant K = Kelvin (temperature) = 0 Kelvin (no negative #s) = - 273 C T = 0.0029 mK / 550 x 10 m = 5272.7 ~ 5300 K - Note that the surface temperature of the Sun is ~5800K - Never stare at the sun! Energy of Light 19 E = hf ; h = Planck, f = frequency J = jewels E red= (6.625 x 10-34Js) (4.3 x 10 cycles/s) = 2.85 x 1019J Note: shorter wavelengths higher frequencies & energies; f and E Spectra Kirchoffs (Three) Laws of Spectral Analysis refer to handout; ONLY NEED TO KNOW HYDROGEN SPECTRUM 1. Light from a hot, dense gas or solid object, when passed through a prism, produces a merging rainbow of colours = continuous spectrum 2. A hot-low density gaseous element produces bright coloured lines on a dark background = emission spectrum 3. When light having a continuous spectrum passes through a cooler gas, the gas absorbs specific wavelengths = dark lines on a rainbow background = absorption spectrum The Bohr Model of the Hydrogen Atom 29 - Proton carries positive charge - Electron carries negative charge - 1913: Electron is in circular orbit around the proton Add APPROPIATE amount of energy to atom electron moves to a higher PERMITTED orbit (=excited state) The Doppler Effect in Astronomy 35 - Star light waves take spectrum - If the entire pattern of spectral lines is: o Shifted to the blue end of spectrum (blue-shifted) o Shorter distance between wavecrests o Object is moving toward you. - If the pattern is:PCS181 o Shifted to the red end of spectrum (red shifted) = greater distance between wave crests = object moving away from you. Doppler Effect to Determine Velocity 41 - c = speed of light = 3 x 10 m/s - = wavelength difference between lab & stellar spectra - lab = wavelength on lab spectrum - vr= radial velocity of star - Then, v =r(c x ) / lab - E.g. [(3 x 10 m/s )* (434.1 434) nm] / 434nm = 69.1km/s Radial Velocity Problem WILL HAVE 5 QUESTIONS MC ON TEST. - H spectral line is = 656.2950 nm in the lab. - Same line as = 656.2927 nm in the spectrum of Regulus - Is Regulus approaching or receding? Radial velocity? - This H ine has a LONGER wavelength in the spectrum of Regulus spectrum is red-shifted, moving away from us 8 - Vr= [ (3 x 10 m/s) * (656.2927 656.2850) nm] / 656.2850 nm = 3519.8m/s = 3.5km/s - Using the Doppler Effect, how can you tell that our Sun rotates? - [Insert image: Doppler shift from a rotating planet] Unit 2: Cosmology Distance Units in
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