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Chapter 5 Light & Matter
Terms in this set (60)
The Electromagnetic Spectrum
Gamma, X, UV, Visible, Infrared, radio
rate of energy flow, measured in WATTS
1 watt=1 joule/s
a piece of plastic or glass etched with many closely spaced lines (e.g DVD)
energy of the light comes from the electrical potential supplied to the object
materials that absorb are called opaque
allowing light to pass through
light bouncing off matter
distance from one peak to the next
number of peaks by any point each second,
measured in cycles per second or Hertz
speed of wave
wavelength times frequency
Suppose you watch a leaf bobbing up and down as ripples pass it by in a pond. You notice that it does two full up and down bobs each second. Which statement is true of the ripples on the pond?
They have a frequency of 2 hertz.
Which of the following best describes the fundamental difference between two different chemical elements (such as oxygen and carbon)?
They have different numbers of protons in their nucleus
the strength of a force that a particle would experience at any point in space
light waves travel in vibrations of both electric and magnetic fields
speed of light
(c) about 300,000 kilometers/sec
where light travels, have properties of waves and particles
Suppose you want to know the chemical composition of a distant star. Which piece of information is most useful to you?
the wavelengths of spectral lines in the star's spectrum
The spectra of most galaxies show redshifts. This means that their spectral lines _________.
have wavelengths that are longer than normal
laws of thermal radiation:
1. Stephan Boltzann's Law: Each square meter of a hotter object's surf ac emits more light at all wavelengths.
2. Wien's Law: Hotter objects emit photons with a higher average energy.
According to the laws of thermal radiation, hotter objects emit photons with _________.
shorter average wavelength
radiation with a spectrum whose shape depends only on the temperature of the emitting object
Suppose you look at a spectrum of visible light by looking through a prism or diffraction grating. How can you decide whether it is an emission line spectrum or an absorption line spectrum?
An emission line spectrum consists of bright lines on a dark background, while an absorption line spectrum consists of dark lines on a rainbow background
If we say that a material is opaque to ultraviolet light, we mean that it _________.
absorbs ultraviolet light
If you heat a rock until it glows, its spectrum will be:
a thermal radiation spectrum.
the wavelength of a spectral feature in the absence of any Doppler shift or gravitational red shift
the effect that shifts the wavelengths of spectral features in objects that are moving toward or away from earth
The set of spectral lines that we see in a star's spectrum depends on the star's:
Compared to the Sun, a star whose spectrum peaks in the infrared is:
A spectral line that appears at a wavelength of 321 nm in the laboratory appears at a wavelength of 328 nm in the spectrum of a distant object. We say that the object's spectrum is:
What is the difference between energy and power? What units do we use to measure power?
Energy is what makes matter move. It is measured in joules.
Power is the rate of which the energy flows. Power is measured in watts, which is 1 joule per second
What is a photon? In what way is a photon like a particle? In what way is it like a wave?
A photon is an individual piece of light. A photon is like a particle because they can be counted individually, and can hit surfaces one at a time. They are like waves because they are also characterized by wavelength and frequency,
A photon is a particle of light. Unlike an ordinary wave, light has a smallest unit that cannot be subdivided. However, light also has wavelike properties, such as having characteristic wavelengths and frequencies.
What do we mean when we say that light is an electromagnetic wave? Describe the relationship among wavelength, frequency, and speed for light waves.
We say that light is an electromagnetic wave because light is a vibration of electric and magnetic fields. Because all electromagnetic waves travel at the speed of light, the product of their frequencies and wavelengths is always the speed of light. (This is because the product of frequency and wavelength is always the speed of the wave. For light, that speed is constant.) Mathematically: frequency = speed of light/wavelength
An electromagnetic wave is a synonym for light, because it consists of waves of electric and magnetic fields. Wavelength is the distance from one peak of an electromagnetic wave to the next. Frequency is the number of peaks passing by any point each second. The speed of the waves determine how fast their peaks travel. The speed of a wave can be determined by the wavelength multiplied by the frequency
If you could see infrared light, you would see a glow from the backs of your eyelids when you closed your eyes.
Yes, Our bodies, including our eyelids, emit infrared radiation. Therefor, we would see the infrared light emitting from our eyelids when we closed them
If you have a 100-watt light bulb, how much energy does it use each minute?
Which of the following best describes why the Sun's spectrum contains black lines over an underlying rainbow?
The Sun's hot interior produces a continuous rainbow of color, but cooler gas at the surface absorbs light at particular wavelengths.
Notice that the Sun's spectrum appears brightest (or most intense) in the yellow-green region. This fact tells us __________.
the approximate temperature of the Sun's surface
Suppose we want to know what the Sun is made of. What should we do
Compare the wavelengths of lines in the Sun's spectrum to the wavelengths of lines produced by chemical elements in the laboratory.
Suppose you are listening to a radio station that broadcasts at a frequency of 97 Mhz (megahertz). Which of the following statements is true?
The radio waves from the radio station are causing electrons in your radio's antenna to move up and down 97 million times each second.
Suppose a photon has a frequency of 300 million hertz (300 megahertz). What is its wavelength?
Frequency is related to wavelength by the formula: wavelength ( frequency = speed of light = 300 million m/s. Thus, for a frequency of 300 million hertz, the wavelength is 1 meter, since 1 m ( 300 million /s = 300 million m/s.
Which of the following best describes why we say that light is an electromagnetic wave?
The passage of a light wave can cause electrically charged particles to move up and down.
They are isotopes both atoms have the same atomic number but different atomic mass numbers
number: # protons
mass: #protons and neutrons
Consider an atom of oxygen in which the nucleus contains 8 protons and 8 neutrons. If it is doubly ionized, what is the charge of the oxygen ion and how many electrons remain in the ion?
Charge = +2; number of remaining electrons = 6.
Because oxygen has 8 protons, it must also have 8 electrons when it is neutral. Doubly ionized means two electrons are missing, leaving only 6 electrons and an overall charge of 8-6= +2.
Which of the following conditions lead you to see an absorption line spectrum from a cloud of gas in interstellar space?
The cloud is cool and lies between you and a hot star.
The planet Neptune is blue in color. How would you expect the spectrum of visible light from Neptune to be different from the visible-light spectrum of the Sun?
The two spectra would have similar shapes, except Neptune's spectrum would be missing a big chunk of the red light that is present in the Sun's spectrum
What explains why the sun is a source of X rays?
The temperature of the corona's gas is some 1 to 2 million Kelvin.
Laboratory measurements show hydrogen produces a spectral line at a wavelength of 486.1 nanometers (nm). A particular star's spectrum shows the same hydrogen line at a wavelength of 486.0 nm. What can we conclude?
The star is moving toward us.
Suppose that two stars are identical in every way - for example, same distance, same mass, same temperature, same chemical composition, and same speed relative to Earth - except that one star rotates faster than the other. Spectroscopically, how could you tell the stars apart?
The faster rotating star has wider spectral lines than the slower rotating star.
Fast rotation will widen spectral lines because there is a greater difference in the Doppler shift from the side of the star rotating toward us and the side rotating away from us
In what way is a photon like a particle? In what way is it like a wave?
It's like a particle b/c they can be counted individually and can hit surfaces one at a time. And they're like waves because each one is characterized by the same properties as waves (like wavelength and frequency).
What determines an atom's atomic number? Under what conditions are two atoms different isotopes of the same element? What is a molecule?
A molecule is when atoms of the same element combine.
What is electrical charge? Will an electron and a proton attract or repel one another? Will two electrons attract or repel one another? Explain.
Electrical charge is a fundamental property that describes how strongly an object will interact in electromagnetic fields. Protons and electrons would attract, but electrons and electrons would not attract.
Describe the phase changes of water as you heat it starting from its solid phase, ice. What happens at very high temperatures? What is a plasma?
ice changes to liquid at the melting point; liquid changes to gas at the boiling point, At very high temperatures, sublimation (the process when molecules escape from a solid) and evaporation (when molecules escape from a liquid) occur much easier and more often.
Molecular dissociation, Plasma phase, Fully ionized plasma are the next three phase changes of water with increasing temperature. Plasma is a hot gas including freely moving electrons and positively charged hydrogen and oxygen ions. Basically, it's when the atoms have become ionized (electrons are stripped from atoms)
ex's. solid=desk, liquid=beer, gas=nitrogen, plasma=fluorescent lights
What do we mean when we say that energy levels are quantized in atoms? Under what circumstances can energy level transitions occur?
Quantized means that they are sudden changes with no in-between level.
Energy level transitions can occur only when an electron gains or loses the exact amount of energy that separates two energy levels. Level 1=0-10.2, Level 2=10.2-12.1, Level 3=12.1-12.8 and Level 4= 12.8-13.6, then Ionization meaning the electron escapes the atom completely (ionizing it)
How do we convert a continuous spectrum shown as a band of light (like a rainbow) into a graph of the spectrum?
Through spectroscopy. And then changing them from showing only visible light to showing the amount of radiation, or intensity, at each wavelength.
Describe the conditions that would cause us to see each of the three basic types of spectra. What do we see in the Sun's spectrum shown on the opening page of this chapter?
Continuous: light bulb produces light of all colors Ex. Incandescent light bulb
Emission Line: gas cloud emits light at specific colors depending on its composition and temperature
Absorption Line: Light from a hot source passes through a cooler gas cloud (which absorbs certain wavelengths [colors])
Describe two ways in which the thermal radiation spectrum of an 8,000K star would differ from that of a 4,000 K star.
An 8,000K star would emit a lot more light at every wavelength than the 4,000K- sometimes in places where the cooler star wont emit light at all-making it bluer. (shorter wavelengths).
-Hotter star emits photons with a higher average KE (makes the peaks of the graph at shorter wavelengths for hotter objects).
Describe the Doppler effect for light and what we can learn from it. What does it mean to say that radio waves are blue shifted? Why does the Doppler effect widen the spectral lines of rotating objects?
The Doppler Effect is when the wavelengths of spectral lines are slightly shifted depending on the velocity of the light and whether it is moving towards or away from us as it orbits the Sun. Blue-shifted (closer together) radio waves means the object is moving towards us. The Doppler effect widens the spectral lines of rotating objects because the wavelengths changes from blue or red. Blue-shifted, red-shifted, and non-shifted photons mix together to get how its rotating.
If the Sun's surface became much hotter (while the Sun's size remained the same), the Sun would emit _____ ultraviolet light & ______ visible light than it currently emits
more & more
Radio waves are forms of
solid to gas
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