3.2.2.2 Particles and Radiation: Collisions of electrons with atoms Flashcards
What is the electron volt?
The kinetic energy carried by an electron after it has been accelerated from rest through a p.d. of 1 volt. The energy gained by an electron is equal to the accelerating voltage.
What is an eV equal to?
1eV = 1.6*10^-19 J
What is the ground state?
The lowest energy level an electron can be in
What is an excited electron?
An electron that is in an energy level higher than the ground state.
Which energy levels have the lowest energy?
The one closest to the nucleus
What is excitation?
When an electron gains enough energy to move to a higher energy level.
How can electrons move up an energy level?
If they absorb a photon with the exact energy difference between two levels.
delta E = E_1 - E_2 = hf
(change in E = energy of initial energy level - energy of final energy level = photon energy)
What is ionisation?
When an electron is removed from an atom, the atom is ionised
What is ionisation energy?
The amount of energy needed to remove an electron from the ground state of an atom
What are fluorescent tubes?
They use the excitation of electrons and photon emission to produce visible light.
How do fluorescent tubes work?
They contain mercury vapour, across which a high voltage is applied. This voltage accelerates fast-moving free electrons that ionise some of the mercury atoms, producing more free electrons. When this flow of free electrons collides with the electrons of mercury atoms, the atomic mercury electrons are excited to a higher energy level. When these excited electrons return to their ground states, they lose energy by emitting high-energy photons in the UV range .
What is phosphor coating on the inside of a fluorescent tube for?
The photons emitted by de-excitation have a range of energies and wavelengths that correspond to different transitions of electrons. The coating absorbs these photons, exciting its electrons to much higher energy levels, which then move down the energy levels and lose energy by emitting many lower energy photons of visible light
