# Physics - Spectra

> Source: https://ollybritton.com/notes/a-level/physics/topics/spectra/ · Updated: 2024-08-25 · Tags: physics, school, year-2

## Flashcards
### 2021-07-05
##### 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.

##### What happens when an electron drops an energy level??
A photon is emitted.

##### Why do simple elements have simpler emission spectra??
There are less electron shells and therefore less possible transitions.

##### ![PHOTO EMISSION SPECTRUM](emission-spectrum.jpg) What type of spectrum is this??
Emission.

##### ![PHOTO ABSORPTION SPECTRUM](absorbption-spectrum.jpg) What type of spectrum is this??
Absorption.

##### ![PHOTO CONTINOUS SPECTRUM](continous-spectrum.jpg) What type of spectrum is this??
Continous.

##### ![PHOTO ABSORPTION SPECTRUM](absorbption-spectrum.jpg) 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.

##### 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??
$$
5eV
$$

##### 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.

##### 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 continous spectrum??
When looking directly at a _white_ light source.

##### When will you see an absorption spectrum??
When looking at hot gas.

##### When will you see an emission spectrum??
When looking at a light source through a cold gas.

### 2022-02-02
##### 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.

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