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Physics year 12 > Chapter 12 - Waves 2 > Flashcards

Chapter 12 - Waves 2 Flashcards

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1
Q

What is the principle of superposition

A

“The principle of superposition states that when 2 waves meet at a point, the resultant displacement at that point is equal to the sum of the displacements of the individual waves”

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2
Q

What is constructive interference

A

Where 2 waves superpose and are in phase and the resultant displacement is greater than the original wave

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3
Q

What is destructive interference

A

Where two waves superpose not in phase and the resultant wave has a smaller displacement than the individual waves

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4
Q

What are the conditions required for a constant interference pattern
and how can we remember if path or phase

A
  • constant phase difference
  • same frequency

h in coherent therefore h in phase

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5
Q

What happens when two waves interfere

A
  • there are maxima where 2 waves constructively interfere
  • there are minima where 2 waves destructively interfere
  • maxima and minima are caused by 2 waves having different path differences by travelling different distances from their source
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6
Q

What are the conditions in terms of path and phase difference for waves to constructively interfere

A

where n is an integer:
- the path difference must be n(lambda)
- the phase difference must be 2Pi(n)
I.e the waves are in phase, there is a whole wavelength or phase separating them

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7
Q

What are the conditions in terms of path and phase difference for waves to destructively interfere

A 
Where n is an integer
- path difference = (n +1/2) x (lambda)
- the phase difference is (2n+1)(pi)
I.e. the waves are not in phase 
They are in antiphase
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8
Q

Describe an experiment to test for interference from sound

A
  • play a sound of set frequency through 2 identical and parallel speakers
  • record the intensity of the sound using a microphone as you move across the front of the speakers in a straight line
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9
Q

How to test for interference in microwaves and deduce wavelength

A
  • set up 2 signal generators producing waves of constant frequency which are coherent
  • move an oscilloscope across the front of the experiment and find where the first order maxima is
  • measure distance from centre of first slit to first order maxima
  • measure distance from centre of second slit to first order maxima
  • the difference should be equal to wavelength
  • repeat for other maxima and take an average
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10
Q

What was the importance of the evidence created by Young’s double slit experiment

A
  • it proved the wave-like nature of light rather than particles
  • if particles you would expect no diffraction thus only two bright marks directly in front of slits
  • this is not what was observed
  • interference patterns were observed
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11
Q

How to set up Young’s double slit experiment

A
  • 2 coherent waves are required for an interference pattern
  • a monochromatic light source is shone through a double slit
  • onto a screen
  • the monochromatic light source can be formed using a filter and a single slit
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12
Q

What is the formula for a double slit experiment

A 
Lambda = ax/d
Lambda is wavelength
a is the slit separation
x is the distance between maxima
d is the distance of the screen from the slits
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13
Q

How does a stationary wave form

A
  • when 2 waves of the same frequency move in opposite directions repeatedly and superpose
  • they should ideally be of equal amplitude
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14
Q

Where are nodes and antinodes formed

A
  • nodes are formed when the 2 waves are in antiphase and cancel out to form a stationary point of 0 amplitude
  • antinodes are formed when the 2 waves are in phase and give a point of max amplitude
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15
Q

How to derive wavelength from a stationary wave

A

The wavelength is equal to twice the distance between adjacent nodes

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16
Q

What energy transfer occurs in a stationary wave

A

There is no net energy transfer, only storage of energy

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17
Q

What is the difference between phase difference in progressive and stationary waves

A

Progressive: the phase changes across a complete wave cycle

Stationary wave: all parts of a wave between nodes are in phase, by nodes they are in antiphase

18
Q

Where L is the length of the string what is the wavelength of the the fundamental frequency

A

2L

19
Q

What happens when the harmonic increases

A 
F0 = 1 antinodes
F1 = 2 antinodes
F3 = 3 antinodes
F4 = 4 antinodes etc.
20
Q

Can a stationary wave be formed from longitudinal waves

A

Yes

21
Q

What are the rules of stationary waves in air columns

A
  • always antinodes at open end
  • always nodes at closed ends
  • From this the wavelength can be calculated
22
Q

What is the equation used for calculating wavelength from a diffraction grating

A 
n(lambda) = a sin(theta)
n = order number
Lambda = wavelength
a = gap separation
Theta = angle to maxima
23
Q

define what a coherent source means

A

coherent sources are ones of the same frequency and constant phase difference

24
Q

define path difference

A

the difference in the distance traveled by two separate waves or points on a wave

25
Q

describe three ways stationary waves can be observed

A

they can be observed through

  • a string of constant tension and length attached to a vibration generator
  • water waves bounding off of an end wall and superposing each other
  • sound waves reflecting off a wall
26
Q

describe the difference in energy transfer between stationary waves and progressive waves

A

stationary waves simply store energy

progressive waves transfer energy from one place to another

27
Q

describe the difference in wavelength between progressive and stationary waves

A

in a progressive wave the wavelength is the minimum distance between two parts of a wave oscillating in phase
in a stationary wave wavelength is twice the distance between adjacent nodes

28
Q

describe the difference in amplitude between stationary waves and progressive waves

A

in progressive waves all parts of the wave have the same amplitude over the course of a wave cycle
in a stationary wave the amplitude is at its highest in the middle of an antinode and drops back to 0 at a node

29
Q

define what is meant by the fundamental frequency of a wave

A

the lowest possible frequency for a stationary wave of a given wavelength, usually containing one antinode

30
Q

how to calculate the speed of sound from a resonance tube

A
  • hold a tuning fork above the tube and play a note
  • change the length if the tube until you hear a loud resonant sound
  • when the frequency of the resonant sound is equal to that of the tuning fork the length of the tube not in the water is equal to 1/4(wavelength)
  • from this the speed of the wave can be calculated using the frequency of the tuning fork and 4L
31
Q

graphical methods of analysing young’s double slit experiment

A
  • if changing D, plot D (on x) against x (on y), the gradient is lambda/a
  • if changing a, plot x (on y) against 1/a (on x), the gradient is lambda(D)
32
Q

which direction do the particles vibrate when in a vertical air column with a stationary wave of sound

A

vertically

33
Q

what equation including sinY can be used for double slit and diffraction gratings

A

sinY = lambda/ a

34
Q

what equation including tanY can be used for double slit and diffraction gratings

A

tanY = x/d

35
Q

how do these two trigonometric equations lead to the standard equation for a double slit or diffraction grating

A

tanY = sinY (approx) where D is much greater than a

36
Q

what other use does the diffraction grating equation have

A 
for a known angle you can calculate how many maxima are present
lambda = a sinx/n
thus 
n = a sinx/lambda
n is maxima number
37
Q

what is a stationary wave, define it

A

a stationary wave is a wave which stores but doesn’t transmit energy and is formed of a consistent pattern of nodes and antinodes caused by the interference of progressive waves travelling in opposite directions

38
Q

what is a node

A

A node occurs where the amplitude/displacement is ALWAYS zero, caused by destructive interference from the superposition of progressive waves

39
Q

what is an antinode

A

An antinode occurs where the amplitude of the stationary wave takes the maximum possible value, it is caused by constructive interference from the superposition of progressive waves

40
Q

if we have an interference pattern created by EM or sound waves and the electrical inputs to the loudspeakers etc. are reversed what occurs to the interference pattern

A
  • the intensities of the maxima and minima remain the same
  • there remain the same number of maxima and minima
  • but their positions are reversed
41
Q

how can we find the wavelength of waves where there is just simple interference (as they travel in the same direction/ not stationary waves) and one speaker is moved

A
  • set the speakers up parallel and emitting the same frequency of waves
  • slowly move one speaker back until a maxima occurs on a microphone a set distance from the initial position, mark position
  • continue to move the speaker back until another maxima occurs on the same microphone, mark position
  • the distance between these two positions is equal to the wavelength

Physics year 12 (12 decks)

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