4.4 Waves Flashcards
What is a progressive wave
An oscillation that travels through matter
What’s an example of a progressive wave
Sound
What do progressive waves transfer
Energy but not matter
What’s a transverse wave
Oscillations or vibrations that are perpendicular to the direction of energy transfer
What’s it called when particles in transverse waves are at a maximum displacement from their equilibrium position
graph
Peaks and troughs
What are some examples of transverse waves
Waves in water
Electromagnetic waves
Waves on stretches strings
What’s a longitudinal wave
Oscillations that are parallel to the direction energy transfer
What’s an example of longitudinal waves
Sound waves
Why are longitudinal waves often called compression waves
When they travel through a medium, they create a series of compressions and rarefactions
What’s displacement of a wave
Distance from the equilibrium position in a particular direction (s) [m]
What’s the amplitude of a wave
Maximum displacement from the equilibrium position (A) [m]
What’s the wavelength of a wave
Minimum distance between two points in phase on adjacent waves- peak to peak or compression to another (λ) [m]
What’s the period of a wave
The time taken for a wave to move one whole wavelength past a given point (T) [s]
What’s the frequency of a wave
Number of wavelengths passing a given point per unit time (f) [Hz]
What’s the wave speed of a wave
The distance travelled by the wave per unit time (v or c) [ms^-1]
What’s the wave equation
v=f λ or c=f λ
v/c is the wave speed [ms^-1]
f is the frequency [Hz]
λ is the wavelength [m]
What’s the equation for frequency
f=1/T
f= frequency [Hz]
T= period [s]
What does phase difference describe
The difference between the displacements of particles along a wave or particles on different waves
What’s phase difference measured in
Degrees [°] or radians [π]
what does it mean when particles in a wave are in phase
when particles are oscillating perfectly in step with each other- they have a phase difference of zero
what does it mean when particles in a wave are in antiphase
when particles are oscillating completely out of step with each other- phase difference of 180 degrees or π
what are displacement-distance graphs of a wave sometimes called
a wave profile
what can displacement-distance graphs of a wave be used to determine
wavelength and amplitude of both types of waves
what can displacement-time graphs be used to determine in a wave
the time period and amplitude of both types of waves
when does reflection occur
when a wave changes direction at a boundry between two different media, remaining in the original medie
how can an oscilloscope and microphone be used to determine the frequency of a wave
-oscilloscope is fed a signal using the mic
-timebase can be set on the x axis to represent time and on the y axis to represent amplitude (usually 1cm squares)
-the time taken to complete one full oscillation can be measured and then used to calculate the frequency
how does the wavelength and frequency change during reflection
they dont- they remain the same
when does refraction occur
when a wave changes direction as it changes speed, when it enters a new medium
what is the reflection angle to the normal compared to the incident angle
it is the same
how are the wavelength and frequency of a wave affected during refraction
frequency remains the same but the wavelength changes
why does the wavelength change during refraction
the speed of the wave changes
what is diffraction
the spreading out of a wave front as it passes through a gap
when will maximum diffraction of a wave occur
when the gap that the wave passes through is the same size as the wavelength of the incident wave
what is polarisation
a property unique to transverse waves
when does polarisation occur
when a wave is resticted to one plane only- plane polarised
why can longitudinal waves not experience polarisation
the direction of energy transfer is already in one plane only
how can wave effects be demonstrated
-a ripple tank can be used to demonstrate refraction and diffraction of a wave
-polarisation filters can be used to demonstrate polarisation of visible light
how is the intensity of a progressive wave defined
the radiant power passing at right angles through a surface per unit area
whats the equation and the units of intensity
I=P/A
how is intensity related to the amplitude
I α A^2
how is the intensity of light related to the radius
as light from a point source spreads in a sphere the area is 4πr^2 so I α 1/r^2
what are electromagnetic waves
transverse progressive waves consisting of magnetic and electric fields which oscillate at right angles to eachother
whats the speed of an electromagnetic wave
they can travel through a vacuum and all travel at the speed of light (c) (3.0x10^8 ms^-1)
what are the wavelengths of different electromagnetic waves
gamma-rays - < 10-12 m
x-rays - 1 nm - 1 pm
ultraviolet - 400 nm - 1 nm
visible - 750 nm - 400 nm
near-infrared - 2.5 μm - 750 nm
infrared - 25 μm - 2.5 μm
microwaves - 1 mm - 25 μm
radio waves - > 1 mm
what are the frequencies of different electromagnetic waves
gamma-rays 10^20 - 10^24 Hz
x-rays - 10^17 - 10^20 Hz
ultraviolet - 10^15 - 10^17 Hz
visible - 4 - 7.5x1014 Hz
near-infrared - 1x10^14 - 4x10^14 Hz
infrared - 10^13 - 10^14 Hz
microwaves - 3x10^11 - 10^13 Hz
radio waves - < 3x10^11 Hz
how is the refractive index calculated
n (refractive index) = c (speed of light)/ v (speed of light in medium)
how can the angle of refraction in to a new medium be calculated
n1sinθ1 = n2sinθ2
n1= refracitve index of ray leaving the medium
θ1= angle of incidence
n2= refractive index of ray entering new medium
θ2= angle of refraction
when does total internal reflection occur
at a boundary between two transparent media with no refraction- all of the light incident on the boundary is reflected back into the original medium
what conditions need to be met for total internal reflection to occur
-the light must be travelling from a material with a higher refractive index, to material of lower refractive index
-the angle of incidence of the ray must be above the critical angle
whats the formula for the critical angle
sinC= 1/n (only true when original material is air)
C= critical angle
n = refractive index
what is superposition
when two or more progressive waves meet and overlap, they superpose, producing a single wave
what is the principle of superposition
when two waves meet at a point, the resultant displacement of the wave at that point is equal to the sum of the displacements of the individual waves
what is constructive interference
where the individual displacements are both in the same direction and add together
what is destructive interference
where the individual displacements are in opposite directions, and counteract each other
what is meant when two waves are coherent
when they are emitted with a constant and unchanging phase difference
what is interference
the superposition occurring between two coherent waves
when does the maximum resultant displacement occur between two coherent waves interfering
when the phase difference is an even multiple of π, so the two peaks of the wave combine
when does the minimum resultant displacement of two coherent waves interfering occur
when the phase difference is an odd multiple of π, so one peak and one trough act to cancel each other out
how can superposition and wavelength of sound waves be investigated
two audio signal generators- they will both emit coherent waves in all directions which will overlap and form and interference pattern- loud and quiet regions will be detected
how can superposition and wavelength of light waves be investigated
Young double-slit experiment- laser producing monochromatic light is placed behind a sheet with two small slits- two coherent waves are produces which overlap and superpose creating alternating bright (maxima) and dark (minima) fringes on a screen
what equation can be used to determine the wavelength of the light used during the Young double-slit experiment
λ=ax/d
λ= wavelength of the light
a= distance between the two slits
x= distance between two adjacent maxima
d= distance between the double slits and the screen
how can a diffraction grating be used to investigate the wavelength of a light source
light is able to pass through the transparent slit between the scratches and produces an interference pattern with bright and dark maxima and minima- the number of slits is usually given per cm so needs to be converted into ‘d’ [m]
what formula can be used to determine the wavelength of a light source through a diffraction grating
dsinθ=nλ
d= distance between each slit in metres
n= the order of maxima
θ= angle between the 0th and nth maxima
λ= wavelength
how are stationary waves formed
stationary waves are formed when two progressive waves with the same frequency, (and ideally amplitude) travelling in opposite directions superpose
what are nodes in stationary waves
points in stationary waves which always have zero amplitude
what are antinodes in stationary waves
points in a stationary waves which always have maximum displacement
how far apart are adjacent nodes within a stationary wave
half a wavelength
whats the frequency throughout a stationary wave
the same everywhere apart from the node where it is 0
whats the phase difference between two points in a stationary wave
180°n, where n is the number of nodes between the two points
how can a stationary wave be produced in a stretched string
-string is taught over a pulley
-vibration generator is used to oscillate the string in a coherent manner
-adjust frequency until a stationary wave is produced
-the transmitter and pulley ends will be nodes with a node-antinode pattern
how can a stationary wave be produced using microwaves
a microwave transmitter can produce a wave which is reflected off a metal plate- the incident and reflected waves superpose and produce a stationary wave- microwave receiver can be moved between the two to observe maxima and minima patten
how can a stationary wave be produced using sound in an air filled tube
a tuning fork is used to produce a loud sound and is held over the end of the tube- the length of the tube can be adjusted until a stationary wave is produced
how does the stationary wave formed with sound vary depending on the air column
-if the column is open at both ends then there will be an antinode at each end
-if the column is open at one end only then the open end will be an antinode and the closed end will have a node
what is the fundamental frequency of a stationary wave
the lowest frequency of vibration for a given arrangement
whats it called the the wave vibrates at the fundamental frequency
the first harmonic
what happens to a stationary wave as the frequency increases
the vibration pattern will alter as new harmonics are produces
what happens to a stationary wave when the frequency of the vibration isnt a multiple of the fundamental frequency
the stationary waves will not be formed
