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A IB Physics HL > 4&9 Waves > Flashcards

4&9 Waves Flashcards

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1
Q

displacement, x [m]

A

distance in a direction; from equilibrium position

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2
Q

amplitude, Xo [m]

A

max. displacement from equilibrium position

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3
Q

frequency, f [Hz]

A

number of oscillations per unit time

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4
Q

period, T [s]

A

time taken for one complete oscillation

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5
Q

phase difference

A

difference in the position within a cycle

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6
Q

monochromatic

A

single color/wavelength

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7
Q

Simple Harmonic Motion (SHM)

A

acceleration proportional to displacement; directed towards equilibrium position

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8
Q

damping

A

friction takes away energy from an oscillating system

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9
Q

Describe the energy changes taking place during one cycle of an oscillation

A
  1. At max displacement, all Ep
  2. When released, Ep → Ek
  3. At equilibrium position, all Ek
  4. This process is reversed…
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10
Q

resonance

A

a vibrating system causes another system around it to vibrate with greater amplitude at a specified frequency

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11
Q

wavefront

A

line joining (neighboring) points IN PHASE; perpendicular to rays

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12
Q

ray

A

direction in which wave/energy is traveling

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13
Q

transverse vs longitudinal wave

A

T: oscillation of the particles is PERPENDICULAR to direction of wave travel
L: oscillation of the particles is PARALLEL to direction of wave travel

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14
Q

wavelength, [m]

A

distance between:
* adjacent troughs/crests (T)
* adjacent compressions/rarefaction (L)

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15
Q

examples of transverse and longitudinal waves

A

transverse: electromagnetic waves, slinky
longitudinal: sound, slinky

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16
Q

wave speed

A

v = f x λ = λ/T
energy propagated along a wave per second

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17
Q

wave intensity

A

I = P/A
power that travels through a given area as the wave travels through

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18
Q

refractive index (n)

A

n = c/v = light speed in vacuum / light speed in medium = sin(θi) / sin(θr)

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19
Q

the refractive index of air is

A

1

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20
Q

dispersion

A

white light separates into its component colors; because different frequencies have different refractive index

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21
Q

diffraction

A

spreading of waves as they pass through/around an obstacle

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22
Q

reflection

A

when wave incidents on and bounces off an interface; angle of incidence = angle of reflection

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23
Q

diffraction is most significant when

A

the size of the gap is similar to the wavelength [pic]

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24
Q

refraction

A

when wave travels from one medium to another: ∆density → ∆ speed → ∆ direction

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25
Q

Principle of Superposition

A

when two waves meet → resultant displacement = vector sum of the individual displacements

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26
Q

interference

A

when waves from two coherent sources SUPERPOSE (resultant displacement = vector sum of the individual displacements)
* path difference = nλ = constructive
* path difference = (n+0.5) λ = destructive

27
Q

Rayleigh Criterion

A

will be able to resolve (distinguish two sources as being separate) when the max of one diffraction pattern is coincident with the 1st min of the other

28
Q

Distinguishing between standing and traveling waves

A

traveling: TRANSFER ENERGY; can have ANY FREQUENCY

standing: zero net energy transfer; have discrete frequency

29
Q

Describe the nature and formation of standing waves

A

wave travel down the tube→ gets REFLECTED→ INTERFERENCE (superposition) between incident and reflected wave

30
Q

Explain how energy is transmitted in sound wave

A

Particles vibrate in the same direction as energy transfer → causes nearby particles to vibrate

31
Q

Describe the motion of a particle at equilibrium during the passage of the next complete transverse wave

A

Oscillate perpendicular to energy transfer ep→Max→ep→Min→ep

32
Q

Explain the effect of a polarizer on light intensity

A

oscillation of light waves from all directions to ONE PLANE only → intensity halves!!

33
Q

Distinguish between polarized and unpolarized light

A

Unpolarized: electric field vector vibrate in ALL PLANES

Polarized: electric field vector vibrate in ONE PLANE only

34
Q

Explain how polarizing sun glasses reduce glare from a reflecting surface

A

Light is horizontally polarized by reflection → sunglasses have a perpendicular transmission axis to the plane of reflected light → reduce intensity

35
Q

construtive interference

A

waves are IN-PHASE when they meet → produce a greater resultant displacement

36
Q

Two overlapping beams of flashlight fall on a screen but no interference pattern is observed - explain why

A

There IS interference! But since the phase between the two sources is rapidly changing, the interference pattern is also CHANGING TOO RAPIDLY to be observed.

37
Q

optically active substance

A

rotates the plane of polarization of incident polarized light

38
Q

Explain why diamonds sparkle

A

due to TIR!! diamonds have very small critical angle → easier to sparkle

39
Q

Critical Angle

A

angle beyond which TIR occurs
n = 1/sinθc

40
Q

What is the condition for Total Internal Reflection (TIR)?

A

incident angle ＞ critical angle

41
Q

Imagine you’re sitting at the bottom of a swimming pool - explain what you see when you look up

A

can only see limited sight of above water as the rest will be reflection of the bottom due to TIR

42
Q

explain the single slit diffraction pattern

A
  1. waves diffract because even the narrowest slit is much wider than the wavelength of light
  2. waves diffracting away from the slit can be considered as a series of wavelets originating from imagined separate sources one wavelength apart from each other.
  3. these wavelets superpose with each other to produce an interference pattern
43
Q

suggest 3 ways to increase the fringe width of a single slit diffraction?

A

fringe width = θ = λ/b

  1. increase wavelength λ (eg. use red light)
  2. decrease slit width b
  3. moving the screen further away, so that waves travel further distance and spread out more
44
Q

describe and explain the single-slit diffraction pattern of a white (not monochromic) source

A

white central max+colorful other max (violet = shortest λ = least diffracted = nearest to central max, red = longest λ = most diffracted = furthest from central max)

45
Q

Explain how optic fiber works

A

θi ＞θcso light travels down the cable by bouncing off the walls due to TIR

46
Q

range of the visible spectrum’s wavelength

A

380-700 nm

47
Q

In a double slit experiment, there is a missing fringe on the screen - explain why

A

double slit interference is modulated by the single slit diffraction pattern; double’s max + single’s min = 0 intensity

48
Q

describe what happens to the fringe pattern when a double slit is replaced by a diffraction grating (very large number of narrower slits)

A
  • more light get through → brighter fringes
  • more path with destructive interference → shaper fringe
  • smaller b → bigger θ → fringes further apart
49
Q

Doppler effect

A

change in observed frequency of a wave; as a result of RELATIVE motion between source and observer

50
Q

RED shift happens when stars

A

move AWAY from us → longer wavelength→ shifts to red spectrum

51
Q

what happens to the single slit diffraction pattern when a BLUE laser is replaced by a RED laser?

A

θ = λ/b
λ increase → bigger angle of diffraction → wider fringes

52
Q

what happens to the single slit diffraction pattern when the slit if made narrower?

A
  • intensity decrease
  • fringe spacing increase (θ = λ/b)
53
Q

nλ = d sinθwhat do the letters reprsent and when is this formula used?

A

used for diffraction gratings
* n = order of maxima
* d = distance between slits
* θ = angular separation between maxima

54
Q

θ = λ/b = X/Dwhat do the letters reprent and when is this formula used?

A

used for single slit
* θ = angle of diffraction
* λ = wavelength of source
* b = slit width
* X = separaction of sources
* D = distance btwn source and observer

55
Q

sd = λD what do the letters reprent and when is this formula used?

A

used for double slit
* s = distance between fringes
* d = distance between slits
* λ = wavelength of source
* D = distance btwn slit and screen

56
Q

2dn = (m+0.5)λwhat do the letters reprent and when is this formula used?

A

thin film interference (constructive, 1 phase change)
* d = thickness of the film
* n = refractive index** of medium
* m = any integer, ‘thinnest film’ when m=0
* λ = wavelength of the light IN AIR

57
Q

R = λ/∆λ =mNwhat do the letters reprent and when is this formula used?

A

Rayleigh Criterion
* R = resolving power
* λ = wavelength of incident light (m)
* Δλ = difference in wavelength
* m = order of diffraction*
* N = number of slits on the diffraction grating illuminated by incident light)

58
Q

Describe, in terms of molecular movements, how sound travels from our throats to somebody’s ear.

A

the vocal chords in our throat vibrate → disturbs surrounding air → air molecules oscillate as longitudinal waves → collide with our ear drums and make them vibrate at the same frequency

59
Q

path difference

A

the difference in distance travelled by two waves from their sources to a given point.

path difference = nλ = constructive
path difference = (n+0.5) λ = destructive

60
Q

Explain why the pattern seen on a screen when white light passes through double slits is colored

A

white light contains a continuous range of different wavelengths → travel at different angles after diffraction → constructive interference at different places on the screen

61
Q

Explain why anti-reflection coatings on lenses need to be λ/4 thick

A

light reflecting off both surfaces will undergo a phase change of π as the material is less dense than glass → the condition for destructive interference becomes 2d=λ/2

62
Q

What is ultrasound?

A

sound with frequency higher than human can hear

63
Q

What is the assumption behind using ∆f/f ≈ v/c

A

c&raquo_space; v

64
Q

A girl looks at a flat vertical glass window with a think transparent coating. Explain why the light reflected to the girl has one wavelength missing.

A

There is partial reflection at the front surface of the layer AND the glass-layer interface; missing wavelength is where destructive interference between reflected rays occurs

A IB Physics HL (13 decks)

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