Chapter 5 Flashcards
Why do we need to study light?
Light is the only tool we have for studying the universe
What is a disturbance that travels from on point to another?
It’s a wave
How did Rømer study the speed of light?
He studied the timing gaps between eclipses of Jupiter’s moons. He studied the time it took light to reach him from the points where earth was closest and farthest from Jupiter. He then calculated earth’s orbital diameter and came up with a predicted time for the light to hit us. He found that the light was consistently hitting us later then the predicted time.
Who was the first one to see clear evidence of light traveling at a finite speed?
Rømer
What is the speed of light formula?
3 × 10^8 m/s
What is a vacuum?
It’s a region of space that lacks matter
What is the speed of light in a vacuum?
300,000 km/s
How long does it take light to travel between the earth and the moon?
1.3 light-seconds
How long does it take light to travel between the earth and the sun?
8 light-minutes
How far away is the closest star?
4.37 light-years
What is a light-year
The distance traveled by light in a year
Is a light-year a measure of time or distance?
Distance
What is the amplitude of a wave?
The height of the wave from above its undisturbed position
What is the wavelength of a wave?
The distance between one crest and the next
What is the frequency of a wave?
The number of crests that pass a certain point each second
What is the unit of frequency?
Hertz (Hz)
True or False:
Waves with the longest wavelengths have the longest frequencies
False
How are the three physical quantities of the speed of light, frequency and wavelength related?
Wavelength = Speed of light/Frequency
What is a spectrum?
Light spread out by a wavelength
What does wave-particle durability mean?
It means that light is a wave and a particle. It travels like a wave and hits like a particle
What has the longest wavelength in the visible light spectrum?
Red light (700nm)
What has the shortest wavelength in the visible light?
Violet (350nm)
What is the unit used to measure the wavelength of visible light?
Nanometer (nm)
What is the visible spectrum?
Roy G. Biv
What is the electromagnetic spectrum?
The whole range of different wavelengths of light
List the wavelengths in the electromagnetic spectrum from longest to shortest
- Radio
- Microwave
- Infrared
- Visible
- UV
- X-ray
- Gamma
What is the shortest wavelength of light?
Gamma rays
What is the longest wavelength of light?
Radio waves
As wavelength increases, the energy of a photon ________ and its frequency _______
- Decreases
2. Decreases
What are photons?
Particles of light
What is the period of a wave?
The time it takes to complete one cycle (1/F)
What is anything that occupies space and has mass?
Matter
Does a neutron have a positive, negative, or no charge?
No charge
Does an electron have a positive, negative, or no charge?
Negative
What are isotopes?
Atoms with the same number of protons but different number of neutrons
What are molecules?
Groups of atoms bound together by shared electrons
Why are x-rays harmful?
They can penetrate through the skin and muscle
What is the lowest possible energy state of an atom?
Ground state
What is the energy stage above ground state?
Excited state
Why do different elements display different patters of lines in their spectra?
Each element has a unique set of energy states and therefore a unique set of wavelengths that can emit or absorb radiation
What is the Doppler effect?
The change in wavelength of sound or light that is due to the source moving towards or away from the observer
What does it mean if a light is redshifted?
It means that the object is moving away from you and the wavelengths are becoming longer
What does it mean if a light is blueshifted?
It means that the object is moving towards from you and the wavelengths are becoming shorter
What is a blackbody?
An object that absorbs 100% of the radiation that hits it
Using Wien’s Law, explain the color and amount of light changes that are observed as the temperature of a hot, glowing object increases.
As the object gets hotter the color goes from red to blue. It also emits more light at all wavelengths
Why are blackbodies black?
It doesn’t reflect radiation, so it appears black
Why are astronomers are interested in blackbody radiation?
Stars behave like blackbodies and emit radiation in a spectrum similar to the spectrum of an ideal blackbody.
How do electrons move from one orbit to another?
When an atom absorbs a large amount of energy, the electron is no longer bound to the nucleus, and can roam free
What are the atoms that have become positively charged by losing one or more electron called?
Ions
List the three different types of spectra
- Continuous spectra
- Emission spectra
- Absorption spectra
What is the continuous spectra?
A spectrum containing all wavelengths, without specific spectral lines
What is the emission spectra?
A series of bright lines with a dark background
What is the absorption spectra?
A series of dark lines on a continuous spectrum
What does Planck’s Law relate?
The energy of the photon to its wavelength of the wave
What is the equation for Planck’s Law?
E = hc/λ
In the equation E = hc/λ, what does each letter represent?
- E
- h
- c
- λ
- The energy of a photon
- Planck’s constant
- The speed of light
- The wavelength of light
What are the four major properties of a wave?
- Amplitude
- Wavelength
- Frequency
- Speed
What is the speed of a wave?
The velocity of a certain point on the wave
What are blackbody curves?
They are curves that are apart of the blackbody spectrum, Their shape depends on the temperature
Using Stefan-Boltzmann’s Law and Wien’s Law, explain the color and amount of light changes that are observed as the temperature of a hot, glowing object increases.
The higher the temperature, the higher the amount of energy that is radiated
How can we find the Sun’s surface temperature?
By comparing the Sun’s spectrum to the appropriate blackbody curve
How does intensity of light change with distance?
Brightness decreases as the distance from a light source increases
Explain the atomic structure
Atoms have a dense nucleus of protons and neutrons.
Electrons surround the nucleus in a “cloud.”
What kind of information can astronomers obtain by studying spectra?
They can find out the chemical composition of the objects
What information can one obtain using the Doppler effect?
We can find out if an object in space is moving towards or away from us
