5.5 Astrophysics (EM Radiation and Distances) Flashcards
(41 cards)
Can electrons bound to an atom exist in any energy level?
No. Only certain discrete energy levels.
Can electrons have an energy value between two energy levels?
No.
Are all energy levels the same for each element?
No. Each element has its own set of energy levels.
What does it mean when an electron becomes ‘excited’?
It has moved from a lower energy state to a higher energy state.
What is required for an electron to become ‘excited’?
The input of external energy (eg. heat, absorption of photon)
What occurs when an electron is de-excited?
It moves towards the ground state. It releases energy in the form of a photon with a specific wavelength.
All energy level values are negative, with the ground state being the most negative. Why use the negative sign?
To represent the energy required to be inputted to remove the electron from the atom.
(Energy levels) An electron which is completely freed from an atom has an energy equal to what?
0
Emission Line Spectra
A series of coloured lines on a black background.
Continuous Line Spectra
All visible wavelengths of light are present.
Absorption Line Spectra
A series of dark spectral lines against the background of the continuous spectrum, with each line corresponding to a wavelength of light used to excite atoms of that element.
Why are the wavelengths of light produced by de-excited electrons different for each element?
Each element has a unique set of discrete energy levels.
What is spectroscopy?
The technique used to identify elements based on the wavelengths of light emitted when atoms in a gas are excited.
Diffraction grating formula
dsinΘ = nλ
d: diffraction slit distance
λ: wavelength
n: order of maximima
Θ: angle of diffraction
What is the colour of a star affected by?
Its surface temperature
For any object above 0K, objects emit what? [Weins law]
Electromagnetic radiation of varying wavelength and intensity.
What can stars be modelled as?
Idealised black bodies that emit radiation across a range of wavelengths, with a peak in intensity at a specific wavelength corresponding to the colour of the star.
State Wein’s Law
The black body radiation curve for different temperatures peaks at a wavelength inversely proportional to the temperature of the object.
Wein’s Law Equation
λmax T = Wein’s Constant
λmax ∝ 1 / T
λmax: Wavelength of light produced with max intensity (peak wavelength)
T: Absolute surface temperature of the object.
What is the luminosity of a star?
The radiant power output of the star.
What is the luminosity of a star proportional to?
The surface area of the star, or the surface temperature.
State Stefan’s Law
For a black body, the luminosity is proportional to the fourth power of its absolute surface temperature.
Give the equation for Stefan’s law.
L ∝ 4πr²T⁴
L = 4πr²T⁴σ
(σ = stefan’s constant)
If we know the temperature and luminosity of a star, what can we determine, using what law?
The radius, using Stefan’s law.
