Chapter 11/12, Waves Flashcards
What is a progressive wave?
A wave transfers energy without giving a net displacement to the material through which it propagates.
What is a traverse wave?
In traverse waves like light the oscillations occur perpendicular to the direction of energy transfer.
What are the peaks and toughs of a wave?
The points of maximum displacement of a traverse wave.
What is a longitudinal wave?
A wave where oscillations are parallel to the direction of energy transfer. e.g. sound.
What is the displacement from a wave?
The displacement from the equilibrium position.
What is amplitude?
The maximum possible displacement.
What is the time period of a wave?
The total time taken for one oscillation.
What is wavelength?
The minimum distance between two points in phase in a wave, e.g. the distance between two peaks.
What is frequency?
The number of wavelengths passing a point per unit time.
What is the wave equation?
v=fλ (wave speed = frequency * wavelength).
What is phase difference?
The difference between the displacements of particles along a wave measured as an angle where π = λ/2.
State the law of reflection.
The angle of incidence is equal to the angle of reflection (angles measured from the normal).
What is refraction?
When a wave slows down or speeds up as it enters a material causing a change in direction.
What is diffraction?
When a wave spreads out as is passes a hole or goes round an obstacle.
When is diffraction most obvious?
When the size of the gap or obstacle is of similar size to the wavelength.
What is polarisation?
When the direction of oscillation is in only one plane.
Why can you not polarise a sound wave?
Because it is not a traverse wave.
Defining equation for intensity?
I = P/A (intensity = power / area).
What is the relationship between intensity and amplitude?
Intensity is proportional to amplitude^2 as velocity of oscillating particles is proportional to E^2 from the K.E. equation.
What is refractive index?
Defined as n=c/v (refractive index = c/speed of light in material) it is a constant for each material which shows how much it bends light.
What does the equation n sin(θ)=k show and how can it be used to find the angle of refraction between two materials?
Shows that refractive index*sin(angle in/out of material) is a constant, can be equated to itself for 2 materials to find the angle of refraction.
What is total internal reflection and what are the requirements for it?
Must travel from medium with high refractive index, the angle of incidence must be greater than the critical angle which is the point where the angle of refraction is 90 degrees.
What is the name given to the process of overlapping waves?
Superposition.
What is the net displacement given from the superposition of two waves?
The sums of the displacement of each wave (note displacement not distance, waves can cancel).
What is destructive interference?
Superposition of two waves where the the displacement of each are in opposite directions.
What is constructive interference?
Superposition of two waves where the the displacement of each are in the same direction.
What is coherence?
When two waves have a constant phase difference.
What is path difference of two interfering waves?
The difference in the distance travelled by the two waves.
If two coherent waves have a path difference of 1 wavelength what is the phase difference?
2π
How did Young prove that light acts as a wave?
By using a lamp and double slits to give an interference pattern.
What are the variables in λ = ax/D and what is the condition for it to work?
λ = wavelength, a = distance between slits, x = distance between centre (0th) and 1st bright fringe and D = distance from slits to the screen. For this to work D»a.
What causes a stationary wave?
When two waves of the same frequency travelling in opposite directions superpose.
What is a node?
Where the net displacement is 0.
What is an anti-node?
Where the net displacement is maximum.
Properties of a stationary wave?
If the amplitude is 0 there is no net transfer of energy, A 2D wave appears to be rotating in 3D space such that the wave compresses then stretches. Nodes are formed where the displacement is opposite and anti-nodes where it is the same.
How is the wavelength of a stationary wave found?
By doubling the distance between two adjacent nodes/anti-nodes.
How can a stationary wave be set up with microwaves?
Use a microwave transmitter and receiver, move a metal plate such that the plate is at a node which will cause the the receiver to be able to detect nodes where there is no displacement (won’t receive any input).
What is the wavelength of the fundamental frequency of a string as a multiple of the length of string?
2 * length.
How can a stationary wave be set up on a string?
Use a pulley with a weight attached to the string at one end and a vibration generator at the other and adjust the vibrations until you have an integer multiple of the fundamental frequency, also a fixed string can be plucked to make it vibrate at its fundamental frequency.
In an open tube what multiple of the wavelength is the length of a tube vibrating at the fundamental frequency?
1/4 * wavelength.
Does the open end of a tube have a node or anti-node and why?
Anti-node because the air is free to move out at the open end
Does the closed end of a tube have a node or anti-node and why?
Node because sound longitudinal and therefore can’t move at the end.
