Waves Flashcards
What is the amplitude of a wave?
the distance from equilibrium to the peak, measured in metres. it is the maximum displacement of the wave.
What is the wavelength?
the distance from one point on one wave to an equal point on the next wave, eg. peak to peak distance measured in metres
What is the time period of a wave?
the time it takes for 1 wave to go through 1 full oscillation, measured in seconds
What is the frequency of a wave?
the number of waves in 1 second measured in Hertz
What is the phase difference?
The phase difference of two waves is the horizontal distance a similar part of one wave leads or lags the other wave. Phase difference is measured in fractions of a wavelength, degrees or radians.
What is wave speed?
how fast the wave is travelling in meters per second.
c = f x wavelength
Give an example of longitudinal waves.
sound
What are the main properties of longitudinal waves?
vibrations are parallel to direction of motion
consist of compressions and rarefactions
Give examples of transverse waves.
EM waves, waves on a string
What are the main properties of transverse waves?
vibrations are perpendicular to the direction of travel
consists of peaks and troughs
sinusoidal waves
What is the speed of an EM wave in a vacuum?
3.0x10^8 m/s
What are polarised waves?
waves which only vibrate in one direction.
what is polarisation evidence of?
transverse waves
What is an application of polarisation?
Polaroid material and the alignment of aerials for transmission and reception
What is a stationary wave?
a wave which does not transfer energy. it has fixed nodes and points between these which oscillate with maximum amplitude called antinodes
What is a node?
a point of no displacement where there is destructive interference and no disturbance
What is an antinode?
a point of maximum displacement (amplitude) and there is constructive interference
How do stationary waves form?
When two waves with the same frequency travelling in opposite directions meet.
When a wave is completely reflected back on itself
When are waves coherent?
when they have the same constant path difference
What is Young’s double slit experiment evidence for?
Wave particle duality - particles acting as waves
What happens during Young’s double slit experiment?
monochromatic light source projected at 2 slits. diffraction pattern shows equal constructive interference peaks and destructive interference troughs.
What would the interference pattern look like for a single source of white light through a single slit?
1 large peak of constructive interference, smaller fringes spread out
Define fringe spacing.
distance between any two consecutive bright fringes or two consecutive dark fringes is called fringe spacing
What safety precautions can be made when working with lasers?
don't look directly at it don't point it at someone else wear eye protection where possible use warning signs that lasers are in use have the shutoff close to hand at all times
Which equation can be used when calculating the angle of diffraction through a diffraction grating?
nλ=dsinθ
What is an application of diffraction grating?
spectrometers
What does it mean if two waves are in phase?
they are oscillating in time with one another
What is path difference?
if two light waves leave a source and hit a screen, the difference in how far the waves have travelled is path difference. it is measured in terms of wavelengths
What does refractive index show?
the higher the refractive index, the slower light can travel through it. the higher the refractive index, the denser the material
What is the refractive index of air?
1
How is refractive index calculated?
n = speed of light in vacuum / speed of light in material
How does light bend when entering a denser material?
towards the normal
How does light bend when entering a less dense material
away from the normal
What is the critical angle?
the angle at which light would totally internally reflect.
sinx = n2/n1
What is a use of total internal reflection?
optical fibres
What is the purpose of the cladding on an optical fibre
stop the core being scratched
prevent multipath dispersion
What are the uses of optical fibres?
phone and TV signals
medical endoscopes
is the refractive index of cladding greater than that of the core and why?
less than because it make it easier for the light to travel through so light would bend away from the normal, making it easier for it to totally internally reflect back into the fibre
Define pulse broadening.
spreading of the light pulses as they travel down the fiber
What is absorption in an optical fibre?
absorption occurs in several specific wavelengths called water bands due to the absorption by minute amounts of water vapor in the glass
What is scattering in an optical fibre?
Scattering is caused by light bouncing off atoms or molecules in the glass
What is a progressive wave?
a wave which transfers energy from one point to another without moving material
What is superposition?
the process by which two waves combine into a single waveform when they overlap
How many nodes and antinodes are there in the 3rd harmonic of a standing wave?
4 nodes, 3 antinodes
How is the wavelength of a stationary wave calculated?
twice the distance between adjacent nodes
Is energy transferred by stationary waves?
no
Derive Snell’s law
sin(x) = opposite / hypotenuse
sin(x) = wavelength / d
dsin(x) = n x wavelength where n is the order
