Quantum Physics Flashcards
What is a photon?
A quantum of energy of electromagnetic radiation.
Define the work function of a metal
It is the minimum photon energy needed to remove an electron from the surface.
What provides evidence for the particle nature of light?
The photoelectric effect.
What provides evidence for the wave nature of light?
Inteference and diffraction
Define an electron volt
Is the energy transferred when an electron travels through a potential difference of one volt.
Define gamma radiation
Photons of electromagnetic radiation emitted from the nuclei.
Define the photoelectric effect
The emission of photoelectrons from a metal surface when it is illuminated by electro magnetic radiation.
Define threshold frequency
It is defined as the minimum frequency for electrons to be emitted from the surface of a metal.
Why are photoelectrons released with a range of Kinetic energies?
It depends on the depth of the electron in the metal. If the photon is absorbed by an electron that is lower in the surface then it will need some of the kinetic energy to actually get to the surface.
What is the effect of increasing the intensity of a source on the photoelectron’s kinetic energies.
-Increasing the intensity of the source will not alter the kinetic energy of the photoelectrons
-Increasing the intensity will just increase the amount of photoelectrons released per unit time..
…hence the intensity is directly proportional to the photoelectric current.
Define the De Broglie wavelength.
The wavelength associated with a moving particle.
Why do the energy levels in an atom have negative values?
Due to attractive forces within the atom by the atomic nucleus, hence external energy needs to be supplied to emit an electron from the atom; zero energy results in ‘free’ elctrons.
Describe an explain an absorption line spectrum.
-It’s a continuous spectrum with certain colours missing - these missing parts appear as black lines.
-It happens when light white light goes through a cool gas, like hydrogen.
-photon absorbed (by electron) and electron excited.
-Photon energy is equal to the difference in (energy of two) energy levels.
-Photon energy relates to a single wavelength / single frequency.
-Electron de-excites and emits photon in any direction
Describe and explain an emission line spectrum.
-It looks like a dark background with coloured lines.
-It happens when gas is hot and the electrons are excited to higher energy levels. As they return to lower energy levels they release photons.
-The released photons show up as bright coloured lines. Each colour corresponds to a specific energy jump between levels in the electrons.
-We see a dark background with specific colours that come from the light emitted by the electrons falling back down to lower energy levels.
