Module 5 - 5.5.2 Electromagnetic Radiation From Stars Flashcards
Energy Levels (definition)
The specific energies that electrons can have when occupying specific orbits
Electrons can move to a higher/lower energy level by
absorbing/emitting energy in the form of em radiation
At low temperatures, most electrons will be in the — energy level
lowest (n=1)
Excitation (definition)
De-Excitation (definition)
- when an electron moves from a lower to a higher energy level by absorbing energy
- when an electron moves from a higher to a lower energy level after releasing energy
- The energy released in de-excitation is emitted as …
- emitted – can have …
- larger energy transition = …
- emitted as em radiation of a specific frequency depending on the difference in energy between the energy levels
- emitted photons can have a range of wavelengths spanning the whole em spectrum
- larger energy transition = longer wavelength of emitted photon
When an electron is infinitely far from the nucleus, its energy is
0 (electron is said to be free from the atom)
As an electron moves towards the nucleus, its energy (2)
- decreases below 0
- it becomes confined within the atom
The value of an energy level is equal to
the amount of energy required to remove an electron from that energy level
The value of the lowest energy level is equal to
the amount of energy required to remove an electron from the atom (ionisation)
most negative value at the ground state
Chemical Composition of Stars (7)
- fusion reaction in star’s core produced photons of em radiation
- photons are constantly absorbed by atoms in gas
- then re-emitted with many different frequencies
- produces a continuous spectrum of wavelengths
- each gas produce a unique pattern of spectral lines
- due to the specific transitions between the element’s energy levels
- can be used to determine the presence of certain elements within the star
A Continuous Spectrum (definition)
A spectrum that appears to contain all frequencies over a comparatively wide range
Continuous Spectra are produced from
hot dense sources
An Emission Line Spectrum (definition)
The spectrum of frequencies of em radiation emitted due to the electron transitions from a higher energy level to a lower one within an atom of that element
Emission Line Spectra act as (3)
- a fingerprint for an element
- as each element produces a unique emission line spectrum
- due to its unique set of energy levels
An emission line spectrum consists of (2)
- a series of bright lines against a dark background
- each line corresponds to a different wavelength of photon emitted by an electron transition
Emission Line Spectra are produced by
hot low pressure gases
An Absorption Line Spectrum (definition)
The pattern of dark lines in a continuous spectrum from a light source and is caused by light passing through an absorbing medium such as a gas
- the dark lines represent the frequencies absorbed by a medium
The Sun’s atmosphere produces a — line spectrum (3)
- absorption
- since it is not hot enough to produce an emission one
- dark lines in the spectrum are caused by the presence of certain elements (e.g. H, He)
Using a Transmission Diffraction Grating allows for (2)
- more accurate measurements
- since the angular dispersion of the colours will be much greater than using a prism
Dispersion (definition)
The separation of visible white light into a spectrum of its colours
Uses of Transmission Diffraction Gratings (2)
- analyse light from stars
- analyse the composition of a star
The wavelength of em radiation emitted by an object depends on its
temperature
The peak intensity of a star’s emission occurs at (3)
- a specific wavelength (λmax) related to the star’s temperature
- doesn’t mean it is the largest λ emitted by the star
- as surface temperature increases peak occurs at a lower λ
For a graph of intensity against λ, the area under the curve — as – increases (3)
- increases drastically as temperature increases
- since the area represents the total energy emitted by the body
- which is strongly temperature dependent
An Ideal Black Body (definition)
A body that absorbs and emits all wavelengths
(a theoretical object)
Hotter objects tend to be (colour)
Cooler objects tend to be (colour)
- white/blue
- red/yellow
Wien’s Law
λmax ∝ 1/T
Stefan’s Law
The total energy emitted by a black body per unit area per second is proportional to the fourth power of the absolute temperature of the body
If two stars have the same temperature, the star that appears brighter has the
larger diameter
Difficulties in obtaining accurate results for Wien’s and Stefan’s Law (2)
- Earth’s atmosphere only allows certain wavelengths of em radiation through
- telescopes need to be placed at high altitudes to avoid dust and human light pollution
