waves Flashcards
what is frequency?
the rate of complete oscillations
what is amplitude?
the max displacement from the equilibrium position
what is the wavelength ?
the length of one full oscillation
what is path difference?
the difference in distance travelled of two waves
what is a wavefront?
the surface which is used to represent the points where the phase is the same
what is phase?
the position of a certain point on a wave cycle
what is coherence ?
when two waves have the same f, same wavelength and a fixed phase difference
what is superposition ?
when two waves interact, and their amplitudes are either added or subtracted from each other
what is constructive interference?
when two waves meet and their displacements are added
what destructive interference?
when two waves meet and their displacements are subtracted
how are stationary waves formed?
stationary waves are formed from the superposition of two progressive waves, travelling in opposite directions, with the same f, same wavelength and same amplitude
what are nodes
the stationary points on a stationary wave, 0 = amplitude
what happens when a wave is polarised?
A polarised wave can only move in one plane, vertically or horizontally, only transverse waves can be polarised
what is diffraction
the spreading out of waves when they pass through or around a gap
what does huygens’ construction state
every point on a wavefront is a source of wavelets
when is diffraction greatest?
when the wavelength of the wave is closest to the gap it is passing through
how do you find the amount of slits,d?
the distance between the slits divided by 1, it has to be in m
how can electron diffraction be used as evidence of the wave nature of electrons?
-An electron gun accelerates electrons through a vacuum to a crystal lattice.
-Here they interact with small gaps between atoms
-This forms a pattern on a screen behind the crystal
what is an interface?
where two materials meet
how to waves behave at an interface?
the wave could be transmitted, this is where it passes to the next material, and it experiences refraction
the wave could also be reflected, where it bounces off without moving into the next material
what is the pulse echo technique ?
This is where ultrasound (US) waves are reflected when they meet boundaries and different materials.
How is the pulse echo technique used?
-Short pulse US waves are transmitted into the target
-It travels until it reaches a boundary between two mediums, where some is reflected back
-The waves are detected
-The intensities of the detected waves are used to determine the structure, the time taken to be reflected is used to determine distance
what is photoelectricity?
when photoelectrons are emitted from the surface of a metal when light above a certain frequency is shone on it. This occurs due to electrons absorbing a photon and gaining enough energy to be liberated
what is threshold frequency?
the minimum frequency of light required to emit photoelectrons
what is the work function
minimum energy required for electrons to be emitted from the surface of a metal
what does increased intensity do to photoelectron releaese?
It doesn’t change the rate of increase but does change the magnitude.
What does increased exposure of light do to photoelectron release?
It does nothing. Photon energy is transmitted immediately
Why does electrons deeper in the metal lose energy?
This is due to collisions between other particles as it leaves the metal
how do electron and photon interactions to make photoelectrons work, how can you increase the amount emitted?
It is a one-to-one interaction.
Prolonged exposure does nothing because the interaction is immediate.
There is a threshold frequency (work function) to emit a photoelectron.
Increases intensity increases the rate of release of photons.
What is the atomic line spectra and how does it work?
The lines are specific wavelengths of discrete packets of electrons.
Electrons are accelerated in a fluorescent tube, this excites and de-excites an atom which releases a photon. The energies of the photons released correspond to certain wavelengths showing that electrons exist in discrete packets
