Physics - Spectra
OCR A-Level Physics 2022
Flashcards
Photons and electron transitions
When is a photon emitted from an atom?
When an electron makes a transition.
What is the energy of the photon created when an electron drops an energy level?
The difference in energy between the initial state and the new state.
Why do simple elements have simpler emission spectra?
There are less electron shells and therefore less possible transitions.
Identifying spectra
What type of spectrum is this?
What type of spectrum is this?
Why do you see absorption lines?
Why do you see absorption lines?There’s a very limited frequency/wavelength of light that’s the exact amount of energy required to cause a transition.
Energy levels and transitions
If an electron is at a $-12eV$ energy state and the next state is $-7eV$, what’s the exact amount of energy required to push it up the state?
If a photon has a frequency slightly too big or too small to push an electron to the right state, what happens?
Nothing, the electron stays in the same place.
Observing spectra
How can you separate out the light from stars into a spectrum?
Diffract the light by passing it through a small slit.
When will you see a continuous spectrum?
When looking directly at a _ white _ light source.
When will you see an emission spectrum?
When looking at a light source through a cold gas.
Describing spectra and their causes
How would you describe, in words, an absorption spectrum?
A continuous spectrum with dark absorption lines at specific wavelengths.
How would you describe, in words, an emission spectrum?
Individual lines of specific wavelength EM radiation.
What causes emission lines?
An electron making a transition to a lower level and emitting a photon.
What causes absorption lines?
Photons being absorbed at specific wavelengths and then later re-emitted in a random direction.
Do absorption lines tell you about the star you’re looking at, the gas in front of it, or both?
Both.