Astronomy Chapter 2
Terms
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- What is the wave nature of light?
- a way to transfer energy from place without the physical movement of material from one location to another
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Wave characteristics:
Distance between successive wave peaks - Wavelength
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Wave charactistics:
Time between passing wave peaks - Period
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Wave characteristics:
Number of wave peaks passing per unit time (1/Period) - frequency
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wave characteristics:
wavelength x frequency - Wave speed
- what is the speed of light?
- 3e8 m/s
- Sound waves travel by vibrating the molecules between the source and listener. Is this how light travels?
- Light does not require a medium in which to travel⬦ Light can travel thru a vacuum.
- The changing position of a charged particle creates
- “waves†in the field lines.
- Moving charges also produce
- Magnetic fields (accelerating charges).
- magnetic fields force charged particles
- to move (to accelerate)
- ** WHAT CAUSES LIGHT? **
- E&M Waves produce LIGHT!
- If Electromagnetic waves creat light, what creates electricmagnetic waves?
- Accelerating charges (electrons, protons)
- The waves of electric field and that of the magnetic field propogate...
- at right angles to one another.
- While the electric field and magnetic field are at right angles to one another. What direction is the wave's motion?
- 90 degrees from both the electric field and 90 degrees from the magnetic field.
- What is the range of the EM spectrum, from least to most energy?
- Radio, Infared, Visible (Red to Violet), Ultraviolet, X-ray, Gamma
- As energy increases, what happens to the wavelength? frequency?
- wavelength decreases as energy increases. Frequency increases as energy increases.
- Where would microwaves fall on the EM spectrum?
- Between Radio waves and infared.
- Why are optical telescopes built on hill tops or at high elevation?
- Because the ATMOSPHERE ABSORBS some of the light coming from space. Minimizing the atmospheric content between the telescope and space increases the amount of light it will recieve.
- What makes objects emit EM radiation?
- when charged particles change their rate of motion, they emit EM radiation.
- measures the amount of motion of the particles
- temperature
- In other words, the hotter the object...
- the higher its temperature and the MORE movement it's particles have.
- All solid/dense objects emit radiation having a characteristic spectrum called
- blackbody
- Hotter blackbodies are (color)
- Bluer and brighter
- If all bodies emit EM waves, why cant we see one another in a dark room?
- Because the EM radiation given off by the body is in the IR not in the visible spectrum.
- Why is the sun yellow?
- because AT ITS MAXIMUM INTENSITY, it's wavelength is in the yellow visible region.
- Wien's law states that Hotter bodies radiate more strongly at..
- SHORTER WAVELENGTHS (BLUER)
- Mathematically, what is Wien's law?
- Wavelength= .29 cm/ Temp(K)
- Why is wien's law so important?
- Knowing a star's wavelength by simply observing the light it emits, we can determine the star's TEMPERATURE!
- Stefan's law states that hotter blackbodies are...
- brighter (at any wavelength).
- Mathematically, what is stefan's law?
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F = sigma x T4
F= flux
sigma= constant - Experimentally, how is a continuous spectrum produced?
- By passing white light through a slit and through a prism.
- Experimentally, how is a emission line spectra created?
- Passing the light from a heated gas through a slit.
- What does each unique pattern of lines tell us?
- the chemical composition of the gas. Each compound produces a unique spectra.
- Experimentally, how is an absorption line spectrum created?
- passing hot light through a cooler gas and passing it through a slit.
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Kirchoff's Laws:
First law: hot, dense gasses or solids produce a - Continuous spectrum (light bulb)
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Kirchoff's Laws:
Second law- hot rarefied gases produce an... - emission line spectrum.
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Kirchoff's Laws:
Third law- Cool gas in front of a hot continuous source produces an - absorption line spectrum
- What are the three subatomic particles that make up an atom?
- electrons, protons, and neutrons.
- Atoms are mostly....
- empty space. the protons and neutrons are squeezed into a tiny space whereas the electrons circle widely around. EMPTY SPACE IN BETWEEN!
- what makes each atom of a given element unique?
- The number of protons and ELECTRONS!
- *** The Bohr Hydrogen model states that...
- every hydrogen atom has one electron circling a proton.
- How did Bohr suggest the electron remained in orbit?
- by the Columb effect (inverse squared law)
- Bohr suggested that electrons can orbit in particular energy states. How would an electron change energy states?
- Electrons would go from the energy state to more energetic states by absorbing energy (usually a photon). In order to return to the ground state the electron releases this energy (usually in the form of light).
- That energy (which is added or released when the electron changes orbit levels) is
- photons of light
- Atoms can only absorb or emit photons having energy exactly equal to
- the energy difference between electron orbits
- High energy photons correspond to short wavelength light and may boost the electron so much that it is completely ejected from the atom! This process is called?
- Ionization
- TO CLARIFY: Every e- “transition†corresponds to
- a unique wavelength.
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In modern quantum mechanics:
Electrons are not just particles, but also - waves, without exact locations
- Moving sources, like fire trucks and race cars, change pitch as they go by⬦ This phenomenon is known as?
- Doppler effect
- As an object passes you, does the pitch go up or down
- down
- Doppler shift: Stars moving toward us appear what color? Those moving away appear what color?
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Blue (Blue-shifted)
Red (Red-shifted) - What can we determine by spectroscopy of the light we observe from stars?
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Chemical composition (spectral lines)
Temperature (blackbody)
Velocity (doppler)
Rotation rate (doppler)
Pressure (spectral lines)
Magnetic field (Zeeman effect)