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Waves
What is a progressive wave?
An oscillation that travels through matter, transferring energy from one place to another without transferring matter
What are the 2 types of progressive waves?
Transverse and longitudinal
Describe transverse waves
Oscillations are perpendicular to direction of wave travel
Describe longitudinal waves
Oscillations are parallel to direction of energy transfer
What is the definition of displacement?
Distance from equilibrium position in a particular direction
What is the definition of amplitude?
Maximum displacement from origin
What is the definition of wavelength?
Minimum distance between 2 adjacent points on a wave oscillating in phase
What is the definition of period?
Time taken for a full oscillation of 1 wavelength to pass a point
What is the definition of frequency?
Number of complete oscillations passing a point per unit time
What is the definition of wave speed?
Distance travelled by a wave per unit time
What is phase difference?
Difference in displacement of particles along a wave, or in 2 different waves
What is phase difference measured in?
Radians
What does it mean for particles to be in phase?
They oscillate in step with each other
Phase difference is a multiple of 2pi
What does it mean for 2 particles to be in antiphase?
Oscillating half a wavelength out of step
phase difference of pi
What does it mean for 2 particles to be out of phase?
phase difference of d/wavelengthx2pi where d is separation in wavelength between 2 particles
What formula links frequency and period of a wave?
f=1/T
What formula links wave speed, frequency, and wavelength?
V =f x lamda
Can progressive waves be reflected?
Yes
What does it mean for a wave to be reflected?
A wave changes direction at a boundary between 2 media so it remains in the original medium
What is the angle of the incidence ray equal to?
The angle of the reflected wave
Do wavelength and frequency change when a wave is reflected?
No they stay the same
What does it mean for a wave to be refracted?
The wave changes direction as it changes speed when it enters a new medium
Do frequency, wave speed and wavelength change when a wave is refracted?
frequency remains constant
In denser materials, sound waves speed up and em waves slow down
Therefore wavelength charges
What does it mean for a wave to be diffracted?
Wave front spreads out as it passes through a gap
Do wavelength and frequency change when a wave is diffracted?
No they stay the same
With what size gap will maximum diffraction occur?
When the gap is the same size of the wavelength of the incident wave
What type of wave can be polarised?
Transverse
What does it mean for a wave to be polarised?
Occurs when the oscillation of a wave is restricted to one place only
Why can longitudinal waves not be polarised?
The direction of energy transfer is already in one plane only
What is the definition of the intensity of a progressive wave?
The radiant power passing at right angles through a surface per unit area
What is the equation that links intensity, power and area?
I = p/a
What are the units of intensity?
wm^-2
How is intensity related to the radius of the sphere the light spreads out in?
Intensity is inversely proportional to the square of the radius
How is intensity related to the amplitude of the wave?
Intensity is directly proportional to square of amplitude
What type of waves are electromagnetic waves?
Transverse progressive waves
What 3 properties distinguish em waves from other transverse waves?
All travel at the speed of light
Can travel through a vacuum
Are made up of oscillating magnetic and electric fields
What do em waves consist of?
Magnetic and electric fields which oscillate at right angles to each other
Can em waves travel through a vacuum?
Yes
What speed do all em waves travel at?
3×10^8 ms^-1 r
What is the typical wavelength of a radiowave?
10³
What is the typical wavelength of a microwave?
10^-2
What is the typical wavelength of a infrared wave?
10^-5
What is the typical wavelength of a visible light wave?
0.5×10^-6
What is the typical wavelength of a ultraviolet wave?
10^-8
What is the typical wavelength of an x-ray wave?
10^-10
What is the typical wavelength of a gamma ray wave?
10^-12
What equation links refractive index, speed of light and speed of light in the medium
n=c/v
n= refractive index
What equation refractive index to angles of incidence and refraction?
n1sinø1 = n2sinø2
Where does total internal reflection occur?
At a boundary between 2 transparent media
What is total internal reflection?
All light incident on the boundary is reflected back, none is refracted
What 2 conditions must be met for total internal reflection?
Light must be travelling from a material with higher refractive index to a material with lower refractive index
Angle of incidence must be above the critical angle
What is the formula for the critical angle?
SinC = 1/n
C = critical angle
n = refractive index of material light is travelling in to
Only works when this material is air
What does it mean for 2 progressive waves to superpose?
2 waves meet and overlap, producing a single wave
What is the principle of superposition?
When 2 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 does the resultant displacement depend on?
Whether there is constructive or destructive interference
What is constructive interference?
Where the individual displacements of 2 superposed waves are in the same direction so add together
What is destructive interference?
Where the individual displacements of 2 superposed waves are in opposite directions so counteract each other
What does it mean for 2 waves to be coherent?
They are emitted with a constant and unchanging phase difference
What is interference?
The superposition between 2 convent waves
When does maximum displacement occur between 2 interfering coherent waves?
When phase difference is a multiple of 2pi
When does minimum displacement occur between 2 interfering coherent waves?
When phase difference is an odd multiple of pi
What is a stationary wave?
Formed when 2 progressive waves, with the same frequency and travelling in opposite directions, superpose
What are nodes?
Points which always have zero amplitude
What are antinodes?
Points which always have maximum displacement
Where can nodes and antinodes be found?
Stationary waves
How far apart are 2 adjacent nodes?
Half a wavelength apart
What is the frequency of a wave at the node?
Zero
What is an expression for the phase difference between 2 points on a stationary wave?
180n
N = number of nodes between the points
Do stationary waves transfer or store energy?
Store it
