3 Waves Flashcards
what do waves do
transfer energy from one place to another without transferring matter
what is frequency
the number of oscillations (vibrations) per second
what is period (of oscillation)
the time taken to complete one oscillation
what is amplitude
the largest distance that a point on the wave moves from its rest position
what is wavelength
the distance between two adjacent wavefronts
what is the phase of a wave
describes how far through a cycle the wave is
what is phase difference
a measure of the difference in where two waves are in their cycle
what are transverse waves
causes particles in the medium to vibrate at right angles to the direction of wave motion
what are longitudinal waves
causes the medium’s particles to vibrate in the same direction as the wave’s motion
what is polarised light
polarised light can only travel in one direction
what waves can be polarised
transverse
what are some applications of polarisation
sunglasses, television transmission and reception
how are stationary waves formed
when two progressive waves, each with the same frequency and wavelength, and moving in opposite directions, interfere with each other.
this creates a wave which doesn’t transfer energy from one place to another.
what are nodes
points on a stationary wave that have zero amplitude
what are antinodes
points on a stationary wave with maximum amplitude
what are resonant frequencies
stationary waves can only have certain frequencies - these frequencies = resonant frequencies
when will resonant frequencies happen
when the distance between the two fixed ends in an integer multiple of half wavelengths, ½λ
what is the first harmonic
the first resonant frequency
happens when the distance between the two fixed ends is exactly ½λ
(has 2 nodes and 1 antinode)
= fundamental frequency
what is the relationship between length and frequency
the longer the length of the string the lower the frequency
this is because the longer the length is the longer the half wavelength must be so the lower the frequency
what is the relationship between the mass per unit length and frequency
the larger the mass per unit length the lower the resonant frequency
for the same length of string, waves travel more slowly a through a heavier string, so the frequency must be lower
what is the relationship between tension and frequency
the higher the tension in a string the higher the frequency
this is because waves travel more quickly down a string with higher tension
what does coherent mean
coherent means that the two waves must have the same frequency and wavelength and have a fixed phase relation (usually 0)
when does interference happen
when any two waves are superimposed on one another
what is path difference
the difference in length travelled by the waves to get to a certain point
what happens when the path difference is a multiple of ⋋
the waves will be in phase and we will see constructive interference
what happens when the path difference is a whole number plus half a ⋋
the waves will be exactly out of phase and we will see destructive interference
what does monochromatic mean
all light is of the same wavelength
what is Young’s Double Split experiment
deals with the interference from two monochromatic coherent sources
what is single slit diffraction
when a light is shone though a single slit it diffracts and produces a distinct pattern
(if the wavelength of the light is roughly the same as the width of the single slit)
what does constructive interference cause in single slit diffractions
bright fringes
what do destructive interference cause in single slit diffraction
dark fringes
what happens if the slits width increases
width of central maximum decreases and its intensity increases (because they are less spread out)
what happens to the central maximum if the wavelength increases
width of central maximum will increase and its intensity will decrease (because photons are more spread out)
what is refraction
when light changes speed and bends when it passes from one medium to the next
what is Snell’s law
relates refractive indices to the angles of incidence and refraction
n1 sinθ1 = n2 sinθ2
how does light speed relate to the optical density of the material
the more optically dense a medium is, the slower light travels through it, and therefore the larger its refractive index
what is total internal reflection
at angles of incidence larger than or equal to the critical angle, no light is refracted, instead all of the light is reflected
what are optical fibres
they transmit light by total internal reflection
what is cladding
each fibre has a core of optically dense material that is covered by a layer of cladding with a much lower optical density
this means that the boundary between the two materials has a very small critical angle
what is pulse broadening
caused by both material and modal dispersion
the pulses emerging from the fibre are longer than those entering
how is diffraction different for red and blue light
Red light has a longer wavelength so diffracts more than blue light
The central maxima is a bright white light
