Waves Flashcards
What is a progressive wave?
A wave that transfers energy through space
What is a transverse wave?
A wave in which the oscillations are perpendicular to the direction of wave propagation
What is a longitudinal wave?
A wave in which the oscillations are parallel to. the direction of wave propagation
Give an example of a longitudinal wave
Sound, primary seismic waves
Give an example of a transverse wave
waves on a stretched string, secondary seismic waves, electromagnetic radiation
What are the regions of high pressure in a longitudinal wave called?
Compressions
What are the regions of low pressure in a longitudinal wave called?
rarefactions
What is the displacement of a wave?
The distance of a particle in the medium from its equilibrium position in a particular direction
What is the equilibrium position in wave motion?
The position of the medium when undisturbed by a wave
What is the amplitude of a wave?
Maximum displacement of the medium from the equilibrium position
What is the frequency of a wave?
The number of wave cycles per second OR the number of waves passing a point per unit time
What is the time period of a wave?
Time taken for one complete oscillation OR time for a whole wavelength to pass a fixed point
What is the relationship between frequency and time period?
f=1/T or inverse proportionality
How many radians of phase are there in one complete wave cycle?
2π rad
What term describes a phase difference of zero between two points on a wave?
In phase
What term describes a phase difference of pi radians between two points on a wave?
In anti phase
What is the phase difference between points half a wavelength apart?
180 degrees or π radians
What is the phase difference between points a quarter of a wavelength apart?
90 degrees or π /2 rad
What is an oscillation?
A displacement one way and then the other about an equilibrium position
What is diffraction?
The spreading out of waves after passing through a slit/around an obstacle
What effect does reducing the size of a single slit have on diffraction?
diffracted waves spread out more
What is the effect of decreasing the wavelength on diffraction?
diffracted waves spread out less
What is meant by the intensity of a wave?
Intensity is the energy delivered by the wave per second per square metre normal to the wave
How is the intensity of a wave related to the amplitude?
Intensity is proportional to amplitude squared
How does intensity vary with distance from a point source of waves
inverse square law or I=P/4 π r^2
What is a mechanical wave
A wave that requires a medium
What is the difference between mechanical waves and electromagnetic waves?
EM waves don’t require a medium
What is an electromagnetic wave?
An oscillation of the electric and magnetic fields at right angles to each other
What is the speed of all EM waves in a vacuum/air?
3x10^8 ms^-1
List the regions of the EM spectrum in order of increasing wavelength
Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, Gamma rays
Which two regions of the EM spectrum overlap?
X-rays and gamma rays
State the range of wavelengths (in powers of ten) of radio waves
> 10^-1
State the range of wavelengths (in powers of ten) of microwaves
10^-1 - 10^-3
State the range of wavelengths (in powers of ten) of infrared
10^-3 - 10^-6
state the range of wavelengths of visible light
7x10^-7 - 4x10^-7
State the range of wavelengths (in powers of ten) of ultraviolet
10^-7 - 10^-8
State the range of wavelengths (in powers of ten) of X-rays
10^-8 - 10^-13
State the range of wavelengths (in powers of ten) of gamma rays
<10^-10
Why can’t longitudinal waves be polarised?
longitudinal waves already only have a single direction of oscillation
What is the effect of a polarising filter?
It only transmits the component of the oscillations parallel to the filter
What is the effect of perpendicular polarising filters?
No light is transmitted
Give a use of polarising filters
LCD screens, 3D TV, polarimetry in manufacturing, anti-glare sunglasses
What effect does reflection have on the polarisation of light?
Reflected light is partially polarised in the plane of the surface
What effect does scattering light have on polarisation?
Scattered light is polarised
Which wave property always remains constant when a wave travels from one medium to another?
Frequency
When entering a material with a higher refractive index what happens to wave speed?
decreases
When entering a material with a lower refractive index what happens to wavelength?
increases
What is the definition of the refractive index of a material?
a value calculated from the ratio of the speed of light in a vacuum to that in a second medium of greater density
What are the angles of incidence and refraction measured relative to?
The normal to the boundary
Which way do waves refract when entering a material with a higher refractive index?
Toward the normal
Which way do waves refract when entering a material with a lower refractive index?
Away from the normal
What is the angle of refraction at the critical angle?
ninety degrees
What are the conditions required for total internal reflection?
Wave must be travelling in a material with a higher index and meeting a boundary with a material of lower refractive index.The angle of incidence must be greater than the critical angle
What two phenomena occur when a wave goes from a higher to a lower refractive index at an angle of incidence less than the critical angle?
The ray is refracted and partially reflected
What is the principle of superposition?
When two waves meet at a point the resultant displacement is the (vector) sum of the displacements of the individual waves
What is constructive interference?
When two waves superpose in phase causing an increase amplitude
What is destructive interference?
When two waves superpose in anti phase causing a decreased amplitude
What are coherent sources of waves?
sources that emit waves with a constant phase difference (and the same frequency)
What is an interference pattern?
A pattern of regions of constructive and destructive interference produced by coherent sources of waves
What path difference is required for waves to be in phase?
a whole number of wavelengths
What path difference is required for waves to be in anti phase?
An odd number of half wavelengths
What is the relationship between path difference and phase difference for coherent sources?
(Path difference/wavelength)x2π
What term describes a phase difference of zero between two waves?
In phase
What term describes a phase difference of π radians between two waves?
In anti phase
What is x in the double slit equation ( λ=ax/D)
Fringe seperation
What is D in the double slit equation (λ=ax/D)
Distance between the double slits and the screen
What is a n the double slit equation (λ=ax/D)
Distance between the double slits
What occurs to cause a dark fringe in the double slit experiment?
Destructive interference of the light from each slit
What occurs to cause a bright fringe in the double slit experiment?
constructive interference of the light from each slit
What did Youngs double slit experiment demonstrate about the nature of light?
that light exhibits wave behaviour
What name is given to light of a single frequency/wavelength?
Monochromatic
Why did Young place a single slit before the double slit?
To ensure the light from each of the double slits was in phase
What are the conditions required for a stationary wave to form?
Two waves travelling/propagating in opposite directions superposé with same frequency and similar amplitude
What is an antinode on a stationary wave?
A point where the progressive waves are in phase and constructively interfering resulting in maximum amplitude
What is a node on a stationary wave?
A point where the progressive waves are in anti phase and are destructively interfering resulting in minimum amplitude
How many wavelengths are there between adjacent nodes of a standing wave?
Half a wavelength
What is the phase difference between points either side of a node?
Pi rad/180 degrees
What is the phase difference of points between two adjacent nodes?
Zero
How does phase vary along a progressive wave
Changes continuously across each wave cycle
How does amplitude vary in a stationary wave?
It varies continuously along the wave. It is a maximum at anti odes and a minimum at nodes
How does amplitude vary in a progressive wave?
It is the same at every point along the wave
What type of wave doesn’t transfer energy?
Stationary waves
What is the fundamental frequency of a string?
The lowest frequency which produces a stationary wave on the string
What factors determine the fundamental frequency on a string?
Length, tension and the thickness of the string
Progressive wave
transfer of energy as the result of oscillations of the medium through which the energy is travelling
longitudinal wave
the oscillation of particles is parallel to the direction of travel of the wave
transverse wave
the oscillation of particles is perpendicular to the direction of travel of the wave
mechanical waves
energy is transferred through a medium
displacement
the distance moved from equilibrium for a point on a wave
amplitude
the maximum displacement from the equilibrium position
refraction
when a wave changes direction as it enters a new medium, due to a change in the speed of travel
critical angle
angle of incidence that will produce an angle of refraction of 90 degrees
