Waves Flashcards
What is one use of a polarising filter?
Plastic stress/strain analysis
What is a wave?
A periodic disturbance in a medium
What is the relationship between intensity and amplitude?
Intensity is directly proportional to amplitude
What is malus’s law?
Intensity = initial intensity of light x cos^2 theta
Theta is the angle between the filter and the light relative to the plane of the initial polarised light.
How do you calculate intensity?
Intensity = power / area
Area = 4pi x r^2
What is intensity?
Intensity is the amount of energy arriving in an area of 1m^2 of the surface in 1 second
What is the unit of intensity?
Wm^-2
What is the principle of superposition?
When two or more waves overlap, the resultant displacement at a point is equal to the vector sum of the individual displacement at that point.
What are the conditions that waves must have in order to be coherent
Same frequency
Constant phase difference
What is path difference
Path difference is the extra distance travelled by waves from one source compared to another
V out = ?
R2/R1 + R2 x V in
Phase difference = ?
The fraction if a complete cycle between two points on a wave
What is phase
Phase is the position of a wave, or a point on a wave at a particular moment in time, measured in radians
V = ?
When given frequency and wavelength
V = f x lambda
What are the three key things to form a standing wave
You reflect a wave.
They must have the same frequency and amplitude.
They interfere.
They produce a wave with nodes and antinodes
what is the range of wavelength of visible light?
Red 700nm to Violet 400nm
what is the wavelength of gamma rays
10^-12 m
what is the wavelength of X rays
10^-8
what is the wavelength of ultraviolet
10^-7
what is the wavelength of infra red
10^-4
Intensity is?
Directly proportional to amplitude^2
i=Ka^2
What is the Double-slit interference equation and what are its components?
Y=ax/D Where Y is wavelength Where a is slit separation Where x is fringe width Where D is the distance between the slit barrier and the screen
What are the two path differences that can occur and what do they cause?
Path difference = nY means waves arrive in phase, causing constructive interference and a bright fringe.
Path difference = (n+1/2)Y mean waves arrive in antiphase, causing destructive interference and a dark fringe.
What are the conditions that need to be met for two interfering waves to be coherent?
Give an example of coherence.
The waves must be in phase / have a constant phase difference
Therefore have the same frequency
Laser light is coherent
What are the conditions that must be met for observable interference to occur
Coherent wave sources, I.e. Same frequencies
The interfering waves should be of the same amplitude to ensure good contrast between bright and dark fringes.
What is the equation for diffraction gratings?
dSin@ = nY
Where d is the grating spacing, d=1/number of lines per mm.
Where @ (theta) is the diffraction angle
Where n is the diffraction order (n=1,2,3…)
Where Y is the wavelength of the light
What are the advantages of using multiple slits over a double slit
Interference fringes obtained with double slits are faint and blurred (no definite edge)
Whereas a diffraction grating overcomes these problems. The maxima are brighter because more slits = more transmitted light.
The maxima are very sharp because constructive interference only happens in certain precise directions.
The Young’s double slit experiment gives evidence in…
In favour of the wave theory of light as it demonstrates light being diffracted which only waves can do, not particles.
