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Module 5 - Chapter 19 - Stars II - Coggle Diagram
Module 5 - Chapter 19 - Stars II
Energy levels in atoms
When electrons are bound to their atoms in gas, they can only exist in one of a discrete set of energies
Negative energy levels as external energy is required to remove an electron from the atom.
An electron with zero energy is free from the atom
Ground state - energy level with most negative value (lowest value)
When an electron moves from lower to higher energy level, it's said to be excited
Raising an electron into a higher energy level requires external energy
Moving from higher to lower energy level means electron loses energy. To conserve energy, a photon is emitted (de-excitation)
Electrons prefer lowest energy level, so always return to it
Spectra
Emission line spectra - each element produces a unique emission line spectrum because of its unique set of energy levels
Continuous spectra - all visible frequences/ wavelengths are present. Atoms of heated solids produces this
Absorption line spectra - has series of dark spectral lines against the background of a continuous spectrum. Line have same wavelength as bright emission spectral lines
Emission spectra
When the electrons drop back into lower energy levels they emit photons with a set of discrete frequencies specific to the element
Energy excited electrons
Emission line spectrum is produced - each line corresponds to photons with specific wavelenght
Absorption line spectra
Formed when light from a source that produces a continuous spectrum passes through a cooler gas.
As photons pass through gas, some are absorbed by the gas atoms, raising electron up into higher energy levels, exciting atoms
Only photons with energy equal to difference between different energy levels are absorbed.
Only specific wavelengths are absorbed, creating dark lines in the spectrum
Lines show which photons have been absorbed by the gas atoms
Photons are re-emitted when electron drops back down to lower energy level atom, and they're emitted in a random direction, and not at observer
Absorption line spectrum for any gas is very nearly a negative fo its emission line spectrum. A few lines frome mission line specrum may not be visible in absorption line spectrum
Detecting elements within stars
When light from a star is analysed, its an absorption line spectrum.
Some wavelengths are missing - phtons have been absorbed by atoms of cooler gas in outer layers of stars
If we know line spectrum of a particular element, we can sese whether the element is present in the star
If element is present then its characteristic pattern of spectral lines will appear as dark lines in absorption line spectrum
Diffraction grating
Optical component with regularly spaced slits that diffract and spit light into beams fo different colour
When light passes through a diffraction grating, it's split into a series of narrow beams, each wavelegnth diffracts by difference amount
Fringes produces by double slit aren't very sharp so determining max position is hard
Large number of slits produces a clearer and brighter interference pattern
When white light passes through, it splits into its component colours
Equation
Formation of maxima at a point depends on the path difference and phase difference of waves from slits
d = Slit separation
Largest possible order number
d = 1/lines per metre
Determining wavelength
Measure angle between several maxima and zero-order maxima
Plot graph of sin(theta) against n and this is a straight line through the origin with gradient of wavelength/ slit separation
Black body radiation
At any temp above absolute 0, an object emits EM radiaiton at different wavelengths and different intensities
Hot objects an be modelled as black bodies - object that absorbs all EM radition shined on it, and emits characteristic distribution of wavelenghts at a specific temperature
Surface temperature o a star affects its colour
Wien's displacement Law
For any black body emitter, the peak wavelenght is inversely proportional to the temperature
Wein's constant -
Peak wavelenght reduces as temperature increases
At any temperature above 0k, objects emit EM radiation of varying wavelength and intensity
Stars can be modelled as idealised black bodies that emit radiation actross a range of wavelengths, with a peak intensity at a specific wavelength
Stefan's law
Total power radiated per unit surface area of a black body is directly proportional to the fourth power of the absolute temperature
Stefan constant:
Luminosity is directly proportional to radius^2, Surface area, and T^4
Luminosity - radiant power output of a star
