Edexcel Physics AS Unit 2

Harmonics and Overtones
Depending on the wavelength of a wave,
different numbers of waves will fill in a certain
space. This can be really useful. Lets use an
example of a string from a musical instrument.
The lowest possible frequency standing
wave that can fit on the string will be:
This is called the fundamental
frequency, and it is the longest
wavelength for that string.
Wavelength will = 2 x L.
If we increase the frequency and
decrease the wavelength, the
next wave that will fit will be:…read more

Standing Waves
Standing waves (also known as stationary waves) are set up as a result of the superposition of two
waves with the same amplitude and frequency travelling at the same speed in opposite directions.
The waves are moving, but the position of the crests and troughs are stationary.
We can calculate the speed of a wave using:
v=f
Where:
v = speed (m/s)
f = frequency (Hz)
= wavelength (m)
We can calculate the speed of a wave on a string using:
Where:
v = speed (m/s)
F = tension (N)
M = mass per metre of the string (kg/m)…read more

Reflection and Refraction
The intensity of a wave is proportional to its amplitude squared.
Intensity (Amplitude)2
Laws of Reflection:
1.Angle of incidence = Angle of reflection
2.The image formed by a plane (flat) mirror is the same distance
behind the mirror as the object is in front.
1.The image is laterally inverted and virtual
Rules of Refraction:
A wave speeds up or slows down when it enters a different medium.
If the wave slows down it bends towards the normal.
If the wave speeds up it bends away from the normal.…read more

Snell's Law and the Refractive Index
So we know that waves slow down when they enter optically denser materials, and bend
towards the normal line.
But can we predict how far waves will change direction?
If we label the angle of incidence as i and the angle of refraction as r, then it can be shown
that when travelling from a vacuum into a material, the ratio remains constant for all values
of i and r. This is Snell's Law.
We call the constant from Snell's law the refractive index, n.…read more

Total Internal Reflection
If the angle of incidence is greater then the critical angle, C
for that boundary the wave will totally internally reflect.
The refractive index of a material is given by:
You should know how total internal reflection is used in
optical fibres and reflecting prisms.
Uses of TIR:
There are many uses for TIR starting from the simple
replacement of mirrors with prisms in periscopes to the
complicated world of fibre optics.…read more