Spectra Flashcards
What is the photoelectric effect?
The phenomena where light or electromagnetic radiation can cause electrons to move or to be transferred from one material to another
Does a higher or lower frequency photon have more energy?
A higher frequency has more energy
Why can ultraviolet eject an electron from a metal but orange light cannot?
Because orange light has a lower frequency so does not have enough energy to eject the electron
What is threshold frequency?
fo - The minimum frequency of a photon which causes electron emission
What is the work function?
The minimum energy required to eject an electron from its parent atom
What is irradiance?
The power per unit area of a radiation
What is ionisation energy?
The energy level at which an electron escapes from the electric field of the nucleus
What happens when an electron falls from one energy level to a lower one?
It releases a fixed quantity of energy resulting in a photon of light with a certain energy being released.
What is consistent between all electrons released from an atom? How does this affect the colour spectrum?
The have the same frequency so a single line of a single colour is produced for that atom
What is the emission spectrum?
The colours produced from an atom by a photon when an electron makes a transition to a lower energy level
What is the absorption spectrum?
Black lines produced in a spectrum caused when the vapour of an element absorbs particular photons of light.
Why do the lines appear in the same position for emission and Absorption?
Because the atom can only absorb photons with exactly the same energy as the gap in the energy levels in the atoms.
How does absorption work?
The electrons absorb the energy from the photons and use it to move to a higher energy level producing a black line on the spectrum. If a photon doesn’t have the exact energy for Ana electron it cannot be absorbed so passes through the vapour creating a rainbow on the spectrum.
The higher the energy gap in an atom the _____ the frequency of the photon produced
Higher
What can spectra be used for?
To identify elements present in the atmosphere
The smaller the energy transition the ______ the wavelength of the photon
Longer
What is evidence of light acting as particles?
Photons providing energy in discrete bundles
What is irradiance measured in?
Wm-2
What happens if you double the distance between yourself and a point source?
The irradiance falls to a quarter of it’s original value
What does the inverse square relationship for irradiance apply to?
All electromagnetic radiation
What happens when electrons make the transition from a high energy level to a lower energy level?
A photon if energy is released and the energy of this photon is equal to the energy gap between the two energy levels
What is Ground state ?
The lowest permitted energy level in an atom
What is ionisation level?
The energy level at which an electron escaped from the electric field of a nucleus
What is a point source?
Where light from a point spreads out evenly in all directions
When does an electron have zero potential energy?
When ionisation takes place and it has escaped from the nucleus’s field
Equation for area?
4 pi r (squared)
The smaller the work function the _______ the threshold frequency
Lower
Explain how a line emission is produced?
If an electron is in an excited state it can return to a lower energy level, emitting a photon. Different transitions produce different lines/frequencies of photons
Explain why some line emissions are brighter than others?
As more electrons make those transitions per second so there are more photons produced each Devon and emitted. Producing a brighter line
