waves Flashcards
progressive wave
wave which transfers energy from one place to another with a wave front which travels through the material
longitudinal wave
waves which the particles oscillate in the same direction as energy propagation
transverse waves and give examples
waves where the particle oscillations are perpendicular to the energy propagation i.e electromagnetic waves
frequency
number of waves passing through a point per second
wavelength
distance between two adjacent corresponding points on a wave
amplitude
max displacement of the wave from its equilibrium position
what is the phase difference of a wave and what is it measured in
the amount one wave lags behind another as a proportion of the wavelength. measured in radians or degrees
what do each of the ‘axes’ on an oscilloscope measure
vertical divisions = voltage/amplitude
horizontal divisions = time
refraction
when a wave bends at a boundary between two materials due to the difference in density causing it to speed up or slow down
true or false: a wave can either be refracted or reflected at a boundary, but never both
false: at low angle of incidence most will be refracted, but some will reflect
true or false: diffraction is most noticeable when the wavelength is much larger than the gap the wave is travelling through
false
the most diffraction is seen when the gap and the wavelength are the same size
if the wavelength is much bigger the waves will be mostly reflected
can all waves be polarised
no, only transverse waves
what is the difference between a polarised and unpolarised wave
- polarised waves only contains waves oscillating along one axis
- unpolarised waves can be oscillating in any direction perpendicular to the axis of propagation
describe how a ripple tank might be used to investigate diffraction
- create water waves in the tank
- vary the size of the gap for them to pass through
- note how the direction of the waves passing through changes
polarised light is being passed through a rotating polarisation filter. what would happen to the intensity of the light passing through
it would vary from a maximum (all light passes through) when the axis of polarisation and the axis of the filter line up to a minimum (no light passes through) when the axes are perpendicular
how is intensity defined in terms of power
intensity is power / area
how are intensity and amplitude related
intensity is proportional to amplitude ^2
true / false: all electromagnetic waves have the same time period
false.
they all travel at the same speed - but their wavelengths, frequencies and time periods vary
how fast do electromagnetic waves travel in a vacuum
the speed of light
true or false: the magnetic field and electric field in a electromagnetic wave are parallel to each other
false: the electric and magnetic field are at right angles to each other
put the following in order from highest to lowest frequency
x-rays, radio, microwaves, uv, visible
highest
- x-rays
-UV
- visible
-microwaves
- radio
lowest
which type of EM radiation has a wavelength of approximately 1 Pm
infra red is between 700 nm and 1mm
what is the range of wavelengths commonly known as visible light
300 - 700 nm
true/false: microwaves can be polarised using a metal grid rather than a polarising filter
true - this is because the wavelength of microwaves is sufficiently large than the grid works as a polarising filter
what is meant by the refractive index of a material
- measure of how fast light travels in a material compared to its speed in a vacuum
n = c/v
a beam of light is shone at a boundary between air and glass. as the angle of incidence is increased from0 to 90 what would you see
at 0 all of the light would pass into the material along the normal
the light would then be seen to be refracted
eventually the light would bend so much it would start to be reflected back
what is the name given to the angle of incidence at which light will reflect off a boundary rather than refracting in the medium
the critical angle
sinC = 1/n
waves can ‘superpose’ - what does this mean
two waves in the same place will combine
what is the name given to what happens to light at angles greater than the critical angle
total internal reflection
what are the two types of interference
constructive and destructive
describe an experiment to investigate the principle of superposition using sound
- use two speakers, a moderate distance apart, connected to the same signal generator to transmit sound waves
- walk along a line perpendicular to the speakers- you should hear alternating loud and quiet points
- this is because in some places the waves from each speaker constructively interfere (loud) and in some places its destructive
coherence
have the same frequency and wavelength and a fixed phase difference often 0 in exam questions
if two waves are in phase will they constructively or destructively interfere
constructively
true/false: path difference and phase difference are two names for the same thing
false
path difference is the difference in distance that two waves have travelled in terms of the wavelength
phase difference is the difference in the point in the cycle of two waves as a proportion of a full wave cycle
why is a laser useful in showing interference and diffraction
it produces monochromatic light
what is Youngs double slit experiment
a single source of light directed towards a double slit which creates two coherent beams of light. this interferes as it hits the screen and creates an interference pattern
describe the interference pattern created using white light
the interference pattern would be a repeating coloured spectrum along the screen, with a bright white point directly in front of the slit
increasing the slit width increases the width of the central diffraction maximum true or false
true
what equation relates the wavelength of light to the slit spacing and distance to the screen
lambda = ax/D
a = slit spacing
x = fringe spacing
D = distance to screen
which two properties of light can only be explained if it is a wave
- diffraction
- interference
when shining light through a diffraction grating there is a maximum number of fringes which would be produced. how would you find this maximum number
Nlambda = Dsintheta
rearrange fro n using theta = 90
what is a stationary wave
consist of alternating fixed pattern of nodes (points with zero amplitude) and antinodes (points with maximum amplitude) no energy is transferred across the wave
node
a point with no vibrations in which the resultant amplitude is 0
antinode
a point with maximum vibration in which the resultant amplitude is at maximum
what are the conditions for a stationary wave to be produced
- the waves must be coherent
- they must be travelling in opposite directions
these conditions are often met when a wave is reflected onto itself
give an example of an experiment you could do to show a stationary wave
- use an oscillator to pass a wave along a string which is fixed at one end
- the stationary wave will from when the progressive wave is reflected off the fixed end
give a similarity and a difference between stationary waves and progressive waves
similarity: both have wavelength, frequency, amplitude
difference: stationary waves don’t transmit energy from one place to another
how could you use the formation of stationary waves in a resonance tube to find the speed of sound
- create a closed end pipe using a hollow pipe inside a measuring cylinder contains water
- use a tuning fork producing a known frequency and hold it above the tube
- move the tube up until you find the first position which causes resonance
- this length will be a quarter of the wavelength
- use speed = frequency x wavelength
harmonics
harmonics are points where the stationary wave form doesn’t change because the waves one act direction are reinforcing each other
a stationary wave on a string is made to oscillate at its fundamental frequency (1st harmonic) - how many nodes and antinodes would you see
nodes - 2
antinodes - 1
