lecture 12 (10/10), chapter 6 & 7
Post on 11-Feb-2022
3 Views
Preview:
TRANSCRIPT
1
Next quiz: WednesdayChapters 2-5; emphasis on Chp. 5Newton’s laws of motionNewton’s law of gravitation
No homeworkSample questions at end of lecture files archived online.
Monday, October 10, 2011
Light and TelescopesChapter 6
Monday, October 10, 2011
I. Radiation: Information from Space A. Light as a Wave and a Particle B. The Electromagnetic Spectrum
II. Optical Telescopes A. Two Kinds of Telescopes B. The Powers of a Telescope C. Buying a Telescope D. New-Generation Telescopes E. Interferometry
III. Special Instruments A. Imaging Systems B. The Spectrograph
Outline
Monday, October 10, 2011
IV. Radio Telescopes A. Operation of a Radio Telescope B. Limitations of the Radio Telescope C. Advantages of Radio Telescopes
V. Astronomy from Space A. The Ends of the Visual Spectrum B. Telescopes in Space C. Cosmic Rays
Outline (continued)
Monday, October 10, 2011
5
Wave-like properties:
• Reflection, refraction, diffraction, interference
• Electromagnetic “waves”
Particle-like properties:
• Energy carried in bundles we call “photons”
• Can propagate through a vacuum
Properties of Light
Monday, October 10, 2011
6
“Light” = Electromagnetic Radiation = Photons
Different names for the same thing:
Vocabulary
Monday, October 10, 2011
7
Frequency
The number of peaks which pass you per second. Units: Hz
Monday, October 10, 2011
8
Speed of wave
Speed = distancetime
= wavelength × frequency
c = λ × f = 3 × 105 km/s
Monday, October 10, 2011
Light as Particles• Light can also appear as particles, called
photons (explains, e.g., photoelectric effect).
Monday, October 10, 2011
Light as Particles• Light can also appear as particles, called
photons (explains, e.g., photoelectric effect).• A photon has a specific energy E,
proportional to the frequency f:
Monday, October 10, 2011
Light as Particles• Light can also appear as particles, called
photons (explains, e.g., photoelectric effect).
E = h*f
• A photon has a specific energy E, proportional to the frequency f:
Monday, October 10, 2011
Light as Particles• Light can also appear as particles, called
photons (explains, e.g., photoelectric effect).
E = h*f
h = 6.626x10-34 J*s is the Planck constant.
• A photon has a specific energy E, proportional to the frequency f:
Monday, October 10, 2011
Light as Particles• Light can also appear as particles, called
photons (explains, e.g., photoelectric effect).
E = h*f
h = 6.626x10-34 J*s is the Planck constant.
The energy of a photon does not depend on the intensity of the light!!!
• A photon has a specific energy E, proportional to the frequency f:
Monday, October 10, 2011
Atoms and StarlightChapter 7
Monday, October 10, 2011
Wavelengths and Colors
Monday, October 10, 2011
Wavelengths and Colors
Different colors of visible light correspond to different wavelengths.
Monday, October 10, 2011
12
Electromagnetic Spectrum
Monday, October 10, 2011
13
Electromagnetic Spectrum
Monday, October 10, 2011
14
Electromagnetic Spectrum
Monday, October 10, 2011
15
Rank the following types of radiation is order of increasing 1) wavelength, 2) frequency, and 3) energy:
microwave, visible, x-ray, radio, gamma ray, infrared
A) gamma ray, x-ray, visible, infrared, microwave microwave, infrared, visible, x-ray, gamma ray microwave, infrared, visible, x-ray, gamma rayB) microwave, infrared, visible, x-ray, gamma ray gamma ray, x-ray, visible, infrared, microwave gamma ray, x-ray, visible, infrared, microwaveC) gamma ray, x-ray, visible, infrared, microwave microwave, infrared, visible, x-ray, gamma ray gamma ray, x-ray, visible, infrared, microwave
Monday, October 10, 2011
16
In which way does a photon of blue light NOT differ from a photon of red light?a. Energyb. Speedc. Wavelengthd. Colore. Frequency
Monday, October 10, 2011
17
Some light sources are comprised of all colors (white light).
Other light sources contain just a few colors.
Some are missing just a few colors.
Types of Spectra
Monday, October 10, 2011
18Wavelength
Brightness
Graphical Representation
Monday, October 10, 2011
19
Graphical Representation
Monday, October 10, 2011
Color and Temperature
Orion
Betelgeuse
Rigel
Stars appear in different colors,
from blue (like Rigel)
via green / yellow (like our sun)
to red (like Betelgeuse).
These colors tell us about the star’s
temperature.
Monday, October 10, 2011
Black Body Radiation (1)The light from a star is usually concentrated in a rather narrow range of wavelengths.
The spectrum of a star’s light is approximately a thermal spectrum called a black body spectrum.
A perfect black body emitter would not reflect any radiation. Thus the name “black body”.
Monday, October 10, 2011
Two Laws of Black Body Radiation1. The hotter an object is, the more energy it emits:
F = σ*T4
where
σ = Stefan-Boltzmann constant
F = Energy Flux =
= Energy given off in the form of radiation, per unit time and per unit surface area [J/s/m2];
Energy Flux
Monday, October 10, 2011
Two Laws of Black Body Radiation
2. The peak of the black body spectrum shifts towards shorter wavelengths when the temperature increases.
→ Wien’s displacement law:
λmax ≈ 3,000,000 nm / TK
(where TK is the temperature in Kelvin)
Monday, October 10, 2011
top related