Waves
Waves are when particles oscillate. When viewed they appear like a wave.
This isn't the case for electromagnetic waves
Beware  this takes up half the paper
This isn't the case for electromagnetic waves
Beware  this takes up half the paper
Terminology
Wavelength (λ) m  The smallest distance between two points that are at ther same point of oscillation along a wave
Period (T) s  The time it takes for one wave to complete one whole oscillation
Frequency (f) Hz or s^1  The number of oscillations per second
Displacement (x) m  The distance any part of the wave has moved from rest
Amplitude (x0) m  The maximum distance a wave has moved from rest
Phase Difference (Φ) rad  The difference in angle two waves under superposition are in comparison to each other. Refer to radians to learn how to use them
Period (T) s  The time it takes for one wave to complete one whole oscillation
Frequency (f) Hz or s^1  The number of oscillations per second
Displacement (x) m  The distance any part of the wave has moved from rest
Amplitude (x0) m  The maximum distance a wave has moved from rest
Phase Difference (Φ) rad  The difference in angle two waves under superposition are in comparison to each other. Refer to radians to learn how to use them
Types of Waves
Transverse
Longitudinal
Properties of a Wave
Reflection
The reflected wave has a phase difference of π
Refraction
Waves travel slower through different mediums. This can be judged from it's refractive index
When entered at an angle the wave bends giving an angle of refraction
When entered at an angle the wave bends giving an angle of refraction
Diffraction
Diffraction is when waves bend round objects
Complete diffraction is achieved when the gap is the same length as the wavelength. If the gap is smaller the wave won't pass through
Complete diffraction is achieved when the gap is the same length as the wavelength. If the gap is smaller the wave won't pass through
Wave Speed
The speed of all electromagnetic waves is of course the speed of light which is 300 000 000 m/s and given the symbol c
Wave Intensity / Energy
Light drops in intensity the further from it's source and thus drops in energy it can pass on
This sets up an inverse square law as intensity is inversely proportional to the radius square
This is different to a waves amplitude
If the waves amplitude doubles, the energy quadruples
They are directly proportional
If the waves amplitude doubles, the energy quadruples
They are directly proportional
Electromagnetic Waves
These are waves that can travel through a vaccuum
They possess a magnetic and electrical wave interlocked perpendicular to each other
They travel at the speed of light  3.8 m/s
They are transverse waves
There are seven areas on the electromagnetic spectrum
You need to know their general wavelength and frequency and know the differences between them
They possess a magnetic and electrical wave interlocked perpendicular to each other
They travel at the speed of light  3.8 m/s
They are transverse waves
There are seven areas on the electromagnetic spectrum
You need to know their general wavelength and frequency and know the differences between them
Gamma Rays
 10^16  10^9 m
 3x10^24  3x10^17 Hz
 Produced via nuclear decay
 Detected in a Geiger Tube
 Used in cancer Treatment
Xrays
 10^12  10^7 m
 3x10^20  3x10^14 Hz
 Produced by bombarding metals with high energy electrons
 Detected by photographic film
 Used in CT scans, Xray photography and crystal structure analysis
Ultraviolet
 10^9  3.7x10^7 m
 3x10^17  8x10^14 Hz
 Produced by hot solids and gases
 Detected by photographic film
 Used in disco lights, tanning studios
Visible Light
 3.7x10^7  7.4x10^7 m
 8x10^14  4x10^14 Hz
 Produced by lasers, hot solids and gases
 Detected by the human retina
 Used in communication and for sight
Infrared
 7.4x10^7  10^3 m
 4x10^14  3x10^11 Hz
 Produced by molecules moving
 Detected by photographic film
 Used in remote controls, night vision
Microwaves
 10^4  10^1 m
 3x10^12  3x10^9 Hz
 Produced by a magnetron gun
 Detected in electronic circuits
 Used in microwave ovens, mobiles, radar
Radiowaves
 10^1  10^4 m
 3x10^12  3x10^9 Hz
 Produced by electric fields in aerials
 Detected by resonance in electric circuits
 Used in televisions and radios
For those of you who like a laugh. This is an very cheesy song, join in with the chorus:
http://www.youtube.com/watch?v=bjOGNVH3D4Y&feature=player_embedded
http://www.youtube.com/watch?v=bjOGNVH3D4Y&feature=player_embedded
Polarisation
Transverse waves oscillate on all planes round the normal
This means they can be polarised
This is when only one plane of oscillation is allowed through a polarising filter
This means they can be polarised
This is when only one plane of oscillation is allowed through a polarising filter
Light reflected off water is plane polarised causing glare
This can be proven by holding two polarising filter together and rotating one through 90°
This should make the filters appear black  as no light is theoretically let through
This can be proven by holding two polarising filter together and rotating one through 90°
This should make the filters appear black  as no light is theoretically let through
Malus' Law
Malus' law dictates light intensity through two polarising filters
He uses the cos squared graph, the angle of rotation and the maximum intensity of the light
He uses the cos squared graph, the angle of rotation and the maximum intensity of the light
You will need to learn this!!!!
Using the graph this shows that when the polarised filter are the same way up they will let through maximum intensity and when rotated 90 degrees they let through 0 intensity
Interference
Interference occurs when two waves of the same type superimpose (occupy the same space at the same time)
The resultant wave is the interference pattern and is the net result of the two waves displacements If two waves are coherent: Constructive interference is when the resultant wave's amplitude is double the original amplitude This happens when the waves are in phase Destructive interference is when the resultant wave's amplitude is 0 This happens when the waves are in antiphase Coherence is when two waves have a constant phase difference Phase or path difference is the difference between two waves in their oscillation stage 

The above diagram shows path difference.
At point R and M the two waves are in phase as they have a phase difference of either 0, 2π, 4π
Point N however is when the waves are in antiphase as they have a phase difference of either π, 3π, 5π
Another way of working this out is by the number of wavelengths difference. If a whole number of wavelengths is result then constructive interference will occur. If a half number of wavelengths is the result then destructive interference will occur
At point R and M the two waves are in phase as they have a phase difference of either 0, 2π, 4π
Point N however is when the waves are in antiphase as they have a phase difference of either π, 3π, 5π
Another way of working this out is by the number of wavelengths difference. If a whole number of wavelengths is result then constructive interference will occur. If a half number of wavelengths is the result then destructive interference will occur
Stationary Waves
The name doesn't mean a wave that stands still but a wave that doesn't appear to move  only oscillate in one place
A stationary wave is formed by reflecting a progressive wave at a point of 0 displacement
This reflected wave then superimposes and thus interferes with the original wave
This creates points of complete constructive interference where there is full oscillation  antinode
And points of complete destructive interference where there is no oscillation  node
A stationary wave is formed by reflecting a progressive wave at a point of 0 displacement
This reflected wave then superimposes and thus interferes with the original wave
This creates points of complete constructive interference where there is full oscillation  antinode
And points of complete destructive interference where there is no oscillation  node
Stationary Wave Harmonics
A guitar string when strum is a stationary wave
Harmonics are the stationary waves formed from the most basic which is the 1st or fundamental harmonic
Harmonics are the stationary waves formed from the most basic which is the 1st or fundamental harmonic
The string length is half the wavelength in the first harmonic
The string length is the wavelength in the second harmonic etc.
Stationary waves are also formed in a closed column
The string length is the wavelength in the second harmonic etc.
Stationary waves are also formed in a closed column
The fundamental harmonic is different to a string as the length is a quarter of the wavelength
Young Double Slit Experiment
The wavelength of light has always been hard to measure and Young was the first to device a method of measuring light's wavelength
To do this though the light source has to be monochromatic  same wavelength
To do this though the light source has to be monochromatic  same wavelength
From this experiment Young derived the equation:
λ = ax D Where a is the distance between the centres of the two slits in metres x is the distance between the centres of two bright patches in metres D is the distance between the slit and the screen in metres This experiment has flaws because it's subjective as to where the centre of the bright patches are meaning the wavelength is just a guess in the end 
Diffraction Grating
Diffraction Grating is a method much better for measuring the wavelength
You don't need to know how one works in the exam, however:
You don't need to know how one works in the exam, however:
Light gets put into a single beam by the collimator. This is then diffracted by the diffraction grating. The eye piece then rotates round to all the points of constructive interference
These points of constructive interference are called orders
The first order is the first time constructive interference is recorded from the centre
These points of constructive interference are called orders
The first order is the first time constructive interference is recorded from the centre
The resulting equation is nλ = dsinθ
where n is the order number
d is the spacing between the slits (If there are 500 slits per mm then there is 1/500 mm between slits)
θ is the angle the order has been seen at
Just like Young's Modulus the further from the centre you get  the less decipherable the orders get before they become too hard to register
where n is the order number
d is the spacing between the slits (If there are 500 slits per mm then there is 1/500 mm between slits)
θ is the angle the order has been seen at
Just like Young's Modulus the further from the centre you get  the less decipherable the orders get before they become too hard to register