Yr 13 - Astrophysics & Cosmology (5.5.6 - 5.5.9) Flashcards
Isotropic
The same in all directions
Homogeneous
Of uniform density
Hubbles Law
Velocity = H0 x Distance
H0 (H naught) = Hubbles constant
3 tests for big bang theory
- Galaxies should be moving apart as space expands
- CMB (cosmic microwave background) radiation from the big bang should be detected. (CMB is left over radiation from Big Bang)
- The light elements (H, He & Li) should have been made in the first minutes of the universe.
(77% hydrogen, 23% helium, Lithium trace)
What is CMB radiation?
Leftover radiation from the big bang.
Electron Energy Level
A discrete energy that an electron must exceed to pass through or equal to remain on energy level.
Ground State
Lowest electron energy level of an atom
What happens to the energy when an electron goes down an energy state/s?
Energy is released as a single photon.
- Energy of photon is exactly equal to change in Ep of electron
1 Electronvolt
Amount of energy transferred to an electron when passed through a PD of 1 volt.
What happens when:
- An electron is exited
- An electron is de-exited (relaxed)
- Moves up energy levels
- Moves down energy levels
What is the Lyman series?
Electron exited from any energy level other than Ground state down to ground state releases Ultraviolet light.
What is the Balmer series?
Electrons exited from first energy level and relaxing back to first energy level releases visible light.
What happens to electron at 0ev?
Electron no longer bound to atom & free to move.
Energy levels only exist at certain energy levels therefore, they are …
Quantised.
- A quanta of energy Is a small indivisible amount of energy.
When is the only time an electron is bound to the atom?
When it has energy equal to an energy level of the atom.
Why are energy levels negative?
Because electrons must gain energy to move up or escape.
- 0ev is set for an escaped electron with 0Ek
1 Parsec
Distance that gives parallax angle of 1 arc second.
What determines the colour of emitted light?
The wavelength of the photon.
How to convert ‘V’ to ‘eV’ and vice verse
V = ev x e
eV = V / e
e = Electron charge (1.6x10^-19_
What is red shift or blue shift etc.
More of a certain energy given off by star.
Red shift = more low energy light given off (Red section of Emission line spectra is larger)
- Learn spectral class types for stars (section before this on Brainscape)
E = hf but how do you calculate E from a energy level diagram?
E_Final - E_Initial = Change E
Can electrons exist anywhere in the atom?
No, electrons can only exist at discreet energy levels (ones unique to the atom)
What does the wavelength of the emitted photon depend on when an electron falls down an energy level?
Wavelength depends on energy difference between the 2 levels.
Emission Spectra
Set of EM frequencies produced by exited atoms
- Visible as bright lines of spectra
- Each atom has a unique spectra representing its energy levels.
Continuous Spectra
Spectra containing all visible EM frequencies (a composition of both emission & absorption spectra)
- Just colours and no lines
Absorption Spectra
Set of EM frequencies absorbed by atom
- Shown as dark lines
What spectra to hot objects emit?
Continuous as both absorption (of heat (infrared)) and emission (photons) which are both em frequencies.
What is an astronomical unit?
Mean distance between earth and sun
Parsec
Distance between SOL and astronomical object with parallax angle. (angle between SOL-object to star-earth)
Next closest star to earth
Proxima Centauri
Diameter of the Milky Way
1x10^5 ly
Distance between milky way & nearest galaxy?
2.5x10^6 ly
Describe the colours on the screen during the diffraction of white light
n = 0 - White light
n = +/- 1 - Blue closest to n=0 from both sides
What is a maxima/minima
Maxima - two or more troughs/peaks of 2 or more waves superpose
Minima - Trough and peak of 2 or more waves superpose
Weins displacement law
λMax = K / T
K = Weins Constant
T = Absolute Temperature
What temperature must an object be above in order to emit em radiation?
> 0 Kelvin
What is a black body
A body that absorbs all em radiation incident on it
- When in thermal equilibrium it emits a characteristic distribution of λ’s
- Can deduce temperature of black body by λ’s emitted.
Luminosity
Total power radiated by a star (same as power)
λMax
λ where the intensity is maximum
Stephans Law
L = 4𝝅r^2𝛔T^4 (In equation booklet)
