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ASTR 1010: TEST TWO
Colors of light
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white light is made up many different colors
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Light and matter interact
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emission
absorption
Transmission
Reflection and Scattering
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Reflection and Scattering
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mirror reflects light in a particular direction
Movie screen scatters light in all directions
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Interaction of light with matter
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Interactions between light and matter determine the appearance of everything around us
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Why is a rose red
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the rose reflect red light
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What is light
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form of radiant energy
light can act wither like a wave or a particle
particles of light are called photon
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Waves
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a pattern of motion that can carry energy without carrying matter along with it
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Properties of Waves
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wavelength: distance btw two wave peaks
frequency: number of times/second that a wave vibrates
light wave is a vibration of electric and magnetic fields
light interacts with charged particles through these electric and magnetic fields.
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light= electromagnetic waves
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a light wave vibration of electric and magnetic fields
lights interacts with charged particles through these electric and magnetic fields.
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Wavelength and frequency
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wavelength= cm
freqency: Ghz
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Light = particles
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particles of light are called photons
each photon has a wavelength and frequency
the energy of a photon depends on its frequency
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Formulas
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wavelength (h) times frequency = speed of light ( c, 3 times 10 to the 8 m/s)
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The higher the proton energy
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the shorter the wavelength
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Structure of matter
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Nucleus contains protons (+charge) and neutrons (no charge)
Electrons (- charge) orbit nucleus at positions set the electrical forces and energy
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Atomic terminology
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Atomic mass: #protons
Atomic mass number: #of protons + neutrons
Molecules: consists of two or more atoms
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Isotope
Ion
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Isotope: same number of protons but different number of neutrons
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Phases of Matter
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Solid (ice)
Liquid (water)
Molecular Gar (water vapor)
Atomic Gas
Plasma
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Phases of Water
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Ionization
Dissociation
Evaporation
Melting
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Phases of Water: Ionization
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stripping of electrons changing atoms into plasma
( highest temperature)
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Phases of Water: Dissociation
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Phases of Water: Dissociation
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Phases of Water: Evaporation
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Breaking of flexible chemical bonds
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Phases of Water: Melting
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breaking of rigid chemical bonds, changing solid into liquid
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Phase and Pressure
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phase of a substance depends on both temperature and pressure
More than one phase is present ( Often)
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Energy stored in atoms
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Electrons in atoms are restricted to particular energy levels/states
electrons prefer lower energy levels
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How is energy stored in atoms
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the only allowed changes in energy are corresponding to a transition btw energy levels
when going down an energy level, an electron emits a photon, ( which frequency related to the diff. in energy levels.)
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how is energy stored in Atoms
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a photon that corresponds exactly to an energy level can be absorbed, allowing electrons to move up an energy level.
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Speed
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rate at which objects moves
S=d/t
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Velocity
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speed and direction
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Acceleration
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any change in velocity this means a change in speed or change in speed or a change in direction or both.
The altitude of acceleration is m/s squared
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Acceleration of Gravity
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all falling objects accelerate at teh same rate
on earth g-10 m/s squared
Galileo showed that g is the same for all falling objects regardless of its mass
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momentum
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mass times velocity
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net force
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the overall force acting on an object ....
the sum of all forces on this object
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Angular momentum
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rotational momentum of a spinning or orbiting object
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Angular momentum
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mass times speed times radius
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A net force applied to an object
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will change its momentum, thus means acceleration ( change in velocity )
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Net force on Object
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Mass times acceleration of object
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Is there a net force when:
1. car coming to a stop
2. a bus speeding up
3. An elevator moving up at constant speed
4. bicycle going around a curve
5. a moon orbiting a Jupiter
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1. y
2. Y
3. N
4. Y
5. Y
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Mass |
amount of matter in an object (kg)
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Weight
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forced measured.
depends on the mass+ forces acting on it ( Newtons)
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my weight is less, my mass is the same
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on the moon
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Astronauts are weightless
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there is gravity, everywhere this is matter
weightlessness is due to constant state of free-fall
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Newton
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realized physical laws on earth and the same for the rest of the universe
discovered laws of motion and gravity
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Newton's 1st Law
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an object moves at constant velocity unless a net force acts to change its speed or direction
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Newton's 2nd Law of Motion
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Net force on object+ mass times acceleration
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Newton's 3rd Law of Motion
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for every force there is always an opposite an equal reaction.
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while driving down the road, a firefly strikes the windshield of a bus, which of he two forces was greater ?
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They are both equal
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Is the force the Earth exerts on you larger, smaller, or the same as the force you exert on it ?
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Earth and I exert equal and opposite forces on each other.
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The acceleration of a recoiling rifle
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smaller than the acceleration on the bullet
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conservation of momentum
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total momentum of interacting object cannot change unless an external force is acting on them
interacting objects exchange momentum though equal and opposite forces
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Conservation of angular momentum
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an object cannot change unless an external twisting force (torque) is acting on it.
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What keeps a planet rotating and orbiting the sun ?
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Earth experiences no torque as it orbits the Sun, so its rotation and orbit will continue indefinelty. ( until phenomena)
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Three basic types of spectra
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Emission line spectra
continuum spectrum
absorption line spectrum
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Spectra of astrophysical objects
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are usually combinations of three basic types of spectra: emission line, absorption line and continuum spectrum.
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continuous Spectrum
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the spectrum shows a smooth, continuous rainbow of light . A graph is also continuous notice that intensity varies slightly at different wavelengths.
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Emission Line spectrum
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We see bright emission lines are specific wavelength (color), but no other light.
The graph shows an upward spike at the wavelength of each emission line.
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Asorption Line Spectrum
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we seek dark absorption lines where the cloud had absorbed lights of specific wavelength (colors).
The graph shows a dip in intensity at the wavelength of each absorption line.
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The spectrum of common Incandescent light bulbs spans all visible wavelengths
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Continuous Spectrum
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a thin or low density cloud of gas emits light only at specific wavelengths that depends on its composition, producing a spectrum with bright emission lines
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Emission Line Spectrum
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A fairly thin cloud of gas between us and a light bulb can absorb light of specific wavelengths, leaving dark absorption lines
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Absorption line spectrum
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Absorption line spectrum
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Chemical fingerprint
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each transition corresponds to a unique photon energy
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chemical fringerprint
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Downward transitions produce emission lines
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chemical finger prints
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Upward transitions produce absorption lines
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chemical fingerprints
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Each type of atom has a unique spectral fingerprint
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Molecules have energy levels
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at their constituent atoms, plus additional energy level b/c they can vibrate and rotate
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Infrared Microwave
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Lots of transitions and spectral features
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Dielectric heating
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bombarding water molecules with photons that make them rotate: this increases thermal energy
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Light can tell us about temperatures...
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of planets and stars
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Thermal radiation
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all large and dense object emit thermal radiation, including stars, planets, and you.
An objects thermal radiation spectrum depends on only one property: its temperature.
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Properties of thermal radiation
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hotter object emit more light at all frequencies per unit area
hotter objects emit photons with a higher average energy.
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what is hotter
a blue star
a red star
a planet that only emits only infrared light
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A Blue star
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Who don't we glow in the dark ?
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People only emit light that is invisible to our eyes
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Reflected Sunlight
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Continuous spectrum of visible light is like the Sun's except that some of the blue light has been absorbed- objects must look red
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thermal radiation
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infrared spectrum peaks at a wavelength corresponding to a temperature of 225 K
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Fingerprint of CO2
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Ultraviolet emission lines indicate a hot upper atmosphere
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Mars |
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Doppler Effect
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Doppler Effect
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we generally measure the Doppler effect from shifts in the wavelengths of spectral lines compared to the emission at rest
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Doppler Effect and star movement
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measuring the shift tell us whether the star is getting closer or further from us
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I measured a line in the lb at 500.7nm. The same line in a star has wavelength 502.8nm. What can I say about the star ?
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It is moving away from me.
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