3.3.1 Waves Flashcards
How do waves transfer energy?
Without the transfer of matter.
c (or v) = ?. What is the worded equation?
fλ. wave speed = frequency x wavelength.
Define transverse wave.
The vibration/oscillation is at 90 degrees (perpendicular) to the wav direction.
Define longitudinal wave.
Vibration/ oscillation is parallel to the wave direction.
Give two examples of transverse waves.
EM spectrum, S-wave earthquakes.
Give two examples of longitudinal waves.
Sound, P-wave earthquakes.
Define the period of a wave.
The time to create 1 complete wave.
How is a stationary wave formed?
When two waves of the same frequency pass through eachother.
What is a node?
The point where the waves cancel and there is no displacement.
What is an antinode?
The point where the waves interfere constructively.
What is the simplest standing wave, what is it referred to as and what is the distance between the nodes?
Your NAN. (Single loop with a node at each end and an antinode in the middle). It is called the fundamental mode of vibration/ fundamental, distance between nodes are 0.5λ.
What is the next standing wave from the fundamental and what is it called?
NANAN, second harmonic.
Give a 6 mark answer for how a standing wave is formed.
- When the crest of the wave on a string arrives at the far end it reverses phase and is reflected, returning as a trough.
- When it once again reaches the vibrator, it reflects, changes phase and once more becomes a crest.
- This is further reinforced by a new crest leaving the vibrator, then the amplitude is increased.
What does raising the tension/ shortening the length do?
Increases the frequency.
What does lowering the tension/ increasing the length do?
Lowers the frequency.
What is polaroid cellulose film used for?
To reduce glare from reflections.
How does polaroid cellulose film reduce glare?
Reflected light is plane polarised, the light is an EM wave so the E-field is reflected in one particular plane. The crystals in the polaroid absorb these waves so the reflection disappears.
What sort of waves are polarised, why can’t we polarise other waves?
Transverse waves can be polarised. Can’t polarise longitudinal waves as they can still oscillate through the crystal structure.
Which waves show the effect of interference?
All.
What does interference rely on and what are some examples?
Relies on waves constructively and destructively interfering. Eg. patterns on a butterfly wing, car paint wraps, oil on water.
What happens when waves pass through a small gap? How do we increase the effect?
Diffraction, more diffraction if gap = λ.
What happens when we pass waves through two gaps close together?
Waves overlap and cause bright spots.
Define constructive and destructive interference.
Crest meets crest, trough meets trough is constructive. Crest meets trough and creates no displacement is destructive.
Who said light was a particle, what did he call it?
Isaac Newton, corpuscle.
Who said light was a wave?
Christian Huygen.
Who proved wave property of light, how? What do we call the nature of light?
Thomas Young in 1801, used double slit experiment. Wave particle duality.
What is a coherent wave/ light source?
The waves are in step with eachother.
What is Young’s double slit equation and what do the letters represent?
λ = ws/D. Fringe separation, w. Slit to screen distance, D. Slit separation, s.
What are the equations for constructive and destructive interference using SP and nλ?
Constructive S1P - S2P = nλ
Destructive S1P-S2P = (n + 1/2)λ
How do we order the beams in the diffraction grating experiment?
Central = 0 order beam. 1st, 2nd etc. symmetrically outwards from 0.
How does diffraction pattern change with λ?
Angle of diffraction between each beam and the zero order beam increases with increasing λ.
How does diffraction pattern change with slit difference?
The angle of diffraction between each beam and the 0 order beam increases with decreasing gap size.
What is the equation for diffraction gratings?
nλ = dsinθ. θ is angle between zero order and 1st, 2nd etc order.
How do you work out the slit separation for a grating of 300 lines/mm?
d = 1/N. d = 1/300x10^3
Angle of incidence = ?. What law is this?
Angle of reflection. Law of reflection.
Define refraction.
The change in direction of a wave due to its speed. Most commonly seen when a wave passes from one medium to another medium of different optical densities.
What is TAGAGA?
Towards (normal) Air Glass Away (normal) Glass Air.
Where does light bend when travelling from less to more optically dense materials and vice versa?
Towards is less to more. Away is more to less.
When light is parallel to the normal what happens to refraction?
Doesn’t apply, since ray continues along the normal.
What is n? What is the equation? Who’s law is this?
n is the refractive index. n = SinI/SinR. Snell’s law.
Define refractive index.
Measure of the bending of a ray of light when passing from one medium to another (relative to a vacuum).
When i < C what happens with the refraction?
Away from normal.
When i = C what happens with the refraction?
Refracts along the boundary at 90 degrees to normal.
When i > C what happens with the refraction?
TIR.
If you send light back along the boundary at 90 degrees to the normal what is r?
r = C.
What is the equation for C?
C = sin^-1(1/n)
Define C.
The critical angle is the angle at which the emergent ray is refracted along the boundary between the two materials (i.e. the angle of refraction is 90 degrees).
What are fibre optics and what do we use them for?
‘Wire for light’, TIR carries light from one end of the wire to another. Eg. medical endoscopes, fibre optic communication.
Where does TIR take place in a fibre optic cable?
At the core-cladding boundary.
What are the refractive indexes of the core and cladding?
Cladding is lower than core.
What do we make the core to reduce absorption?
Optically clear.
Why is cladding needed?
To prevent cross talk from one channel to another, prevents damage to the core.
What do we do to the core to reduce multipath dispersion?
Thin.
Why are fibre optics used for high speed data communication?
Immune to EM interference. No electrical current, no heating. Lower losses per unit length, allows longer distances between repeater amplifiers. No corrosion. Higher bandwidth, more data transmitted.
Define progressive wave.
Transfers energy from one point to another without transferring material/matter.
What is the equation for frequency?
f = 1/T
With waves of the same amplitude but higher freq. explain the effect on an amp/distance graph.
Smaller λ, smaller spread in main peak/more peaks, central peak is higher, because energy conc. over smaller area.
Explain how a bright line is formed by the diffraction grating at the 1st order diffraction angle.
Light from each slit superpose, light from adjacent slits have a path difference of 1 λ, all waves are in phase, constructive interference.
How do you calculate 1st order diffraction angle?
sinθ = λ/d
How do you calculate highest order observed?
n = d sinθ/λ n(max) = d sin90/λ
