Photons & electrons Flashcards
Frequency
The number of complete waves that pass a point per second. Frequency is measured in hertz (Hz).
Example: A frequency of 50 Hz means that 50 complete waves pass a point in one second.
Wavelength
The distance between two consecutive points on a wave that are in phase. Wavelength is measured in metres.
Example: The wavelength of red light is around 700 nanometers.
The photoelectric effect
The process that occurs when light shines on a metal and electrons are ejected.
Significance: It establishes the quantum theory and illustrates the particle nature of light.
A photon
The quantum of energy when the energy is in the form of electromagnetic radiation.
Example: Photons are particles of light with no mass.
Threshold frequency (fo)
The minimum frequency of incident radiation at which electrons will be emitted from a particular metal.
Example: If the threshold frequency is not met, no electrons will be emitted.
Work function of a metal (Wo)
The minimum amount of energy needed to emit an electron from the surface of a metal.
Example: Different metals have different work functions.
Red shift
A shift in the spectra of distant galaxies toward longer wavelengths, i.e. towards the red end of the spectrum.
Example: The red shift of galaxies helps astronomers determine their distance from Earth.
An absorption spectrum
Produced when white light from a source passes through a ‘cool’ gas. It is also referred to as a line absorption spectrum.
An emission spectrum
Produced when electrons ‘fall’ from an orbital of higher energy to an orbital of lower energy. It is also referred to as a line emission spectrum.
