Unit 2 - waves Flashcards
define a wave
transfers energy from one point to another
define wavelength
Wavelength (λ) - the distance from one point of a wave to the same point of the next wave - measured in metres (m)
define amplitude
Amplitude (a) - the distance from the centre of the wave to a peak or trough - measured in metres (m)
define the period of a wave
Period (T) - the time taken for one wave to pass - measured in seconds (s)
define frequency
Frequency (f) - the number of waves that pass a point in one second - measured in Hz
define wave speed
Wave speed (v) - the distance a wave travels in a second - measured in metres per second (ms-1)
what are the four properties that waves show?
reflection, diffraction, refraction and interference.
what is the law of reflection?
angle of incidence = angle of reflection - v, f and λ remain unchanged
what is diffraction?
the spreading out of waves when they go through a gap, or past the edge of a barrier.
does a low frequency diffract more or less than high frequency wave?
diffracts more
what is refraction?
when waves change direction when passing from one medium to another due to a change in velocity. λ and v change, f stays the same.
when does the light bend towards the normal?
Less dense to more dense
what happens when white light refracts?
disperses into continuous spectrum (rainbow of colours) - violet light refracts more than red
what does the amount of refraction depend on?
refractive index of the material
define refractive index
the ratio of the speed of light in a vacuum to the speed of light in the medium (no units)
finish this sentence: Higher the refractive index … the amount of refraction
higher
with Snell’s law what must air always be?
sinθ1
define the critical angle?
the angle of incidence which produces and angle of refraction of 90 degrees.
what is TIR?
occurs when the angle of incidence is greater than the critical angle - e.g. Optical fibres
what is Interference evidence for?
the wave model of light
define coherent
same frequency (connected to the same source) and in phase (peaks meet peaks and troughs meet troughs).
when is maxima produced?
constructive interference takes place - the two waves meet in phase
what must waves do to meet in phase?
must travel some distance but with a whole number of wavelengths
when is minima produced?
when destructive interference takes place - the two waves meet out of phase (peaks line up with troughs)
what must waves do to meet in phase?
must travel some distance but with a whole and a half wavelengths difference
what is a diffraction grating?
clear window with vertical lines on it - cause light passing through to refract and the overlapping waves interfere with one another
why is a laser a good source when using a diffraction grating?
the light is monochromatic (one colour, one frequency) and coherent (same frequency, same phase)
how can you make the maxima further apart?
Use light with a longer wavelength, increase λ - towards the red end of the visible spectrum
Decrease d, the slit separation - have more lines per mm
Move the screen further away for the diffraction grating
define irradiance
the rate at which electromagnetic energy is transferred over a given area - power per unit area
what is irradiance measured in?
irradiance measured in Wm-2
what are the reasons why the irradiance graph may not by completely accurate?
Other light sources in the room providing “background” irradiance
The light source may not be behaving like a point source - may look like a extended source
what is the Bohr model of the atom?
Electrons occupy certain discrete energy levels. They can be excited and therefore move to a higher energy level. The electrons cannot exist between two energy levels.
define ground state
lowest possible energy state of an electron
define energy levels
possible energy state that an electron can occupy
define ionisation
when an electron is given enough energy to escape from an atom
define zero potential energy
highest possible energy state an electron can occupy while still being part of the atom
what is continuous spectra?
caused by heating objects - they produce every colour form red through to violet (if at a high enough temperature)
what is line emission spectra?
black with coloured lines - occurs when electrons in a higher energy level transition to a lower energy level emitting a photon
what is absorption line spectra?
has black lines on a continuous spectrum - occurs when electrons in a lower energy level absorb radiation and are excited to a higher energy level
what provides evidence for the composition of the Sun’s outer atmosphere.
the absorption lines (Fraunhofer lines) in the spectrum of sunlight
how can an electron transition between energy levels?
by either absorbing or emitting (in the form of a proton) which matches the energy change of the electron. Only a certain transitions exist as there is only a certain number of energy levels.
