Topic 5a - Waves And Particle Nature Of Light And Working Scientifically Flashcards
1
Q
Define period
A
Time taken for one complete oscillation
2
Q
Define wavelength
A
Distance between one point on a wave and the same point (with the same phase) on the next wave
3
Q
Define amplitude
A
Maximum displacement from equilibrium position
4
Q
Define frequency
A
Number of complete oscillations per unit time
5
Q
What is the wave equation and how do you derive it?
A
V = frequency x lambda
(Number of waves x wavelength = distance) and divide that by time (or think of it as per second) is made from frequency x wavelength
6
Q
What is a wave
A
A transfer of energy
7
Q
What is a transverse wave
A
The direction of energy transfer is perpendicular to the direction of oscillations of particles/field
8
Q
Why can transverse waves oscillate a field but longitudinal can’t?
A
EM radiation does this
9
Q
The oscillation of what creates an electromagnetic wave
A
A point charge
10
Q
Define a longitudinal wave
A
the direction of energy transfer is parallel to the oscillations of particles
11
Q
[ f ] = ?
A
Hz
12
Q
[ lambda ] = ?
A
Metres
13
Q
What does a displacement - distance graph show
A
A snapshot of a wave, capturing the displacement of lots of particles at that time
14
Q
What does a displacement time graph show?
A
The oscillation of a single particle over time
15
Q
What is the equation for frequency
A
1/T
16
Q
What is the symbol for amplitude and the unit
A
A, metres
17
Q
How many sf do you write every answer to in physics?
A
2
18
Q
Write the equation for speed in symbols
A
V = s/t
19
Q
When a transverse wave is travelling to the left, which way is the future of the wave and which is the past?
A
The right is the future, the left is the past
20
Q
When a transverse wave is travelling to the left, which way is the future of the wave and which is the past?
A
The right is the future, the left is the past
21
Q
Where is the equilibrium position in a longitudinal wave - is there one or are there many?
A
In the middle of the maximum displacement left and right of a particle
Many (as it is defined for every particle whcih is oscillating)
22
Q
What is compression in a longitudinal wave and is it an area or a point?
A
A point of maximum pressure
23
Q
What is the point of rarefaction in a longitudinal wave? And where is it?
A
A point of minimum pressure- it is not a point in space, it is at the centre of the particle with the lowest pressure
24
Q
What is the displacement of a particle at the position of compression/rarefaction?
A
0
25
What happened to create a position of rarefaction?
The particles around the rarefaction were displaced away from the rarefaction
26
What happened to create a position of compression?
The particles around the compression were displaced towards the compression
27
How do you create a graph of a longitudinal wave from a picture like this:
1. Find the displacement of the particles
- do this by reasoning that particles must be moving towards points of compression, and away from points of rarefaction
2. Decide which way to rotate your arrows of displacement
3. Draw a transverse wave over the heads of those arrows
28
What is the wave equation?
V (speed) = frequency (f) x lambda (wavelength)
- this is obvious as it is the number of waves x distance each wave spans per second
29
Does sound travel faster in solid or liquid?
Solid
30
What is the speed of light in a vacuum?
3 x 10^8 m/s
31
What is the speed of sound in air?
330ms^-1
32
What is the frequency of ultrasound?
Above 20 000 Hz
33
What order of magnitude should the frequency of light be?
10^14
34
What 3 things can happen to a wave when it crosses the boundary between 2 materials
Absorbed, reflected, transmitted
35
In what circumstance is a wave mostly reflected when it crosses the boundary between two materials
When there is a very large difference in density between the two materials
36
Exam question to memorise: 6 marker:
Question about wave reflection across a boundary (with examples like echolocation/ultrasound scanning)
1. Pulse is reflected from boundary
2. The reflection is caused by a change in density
3. The Time taken between pulse being sent and received, t, is measured
4. The speed of the ultrasound, v, is known (if it is the speed of light - state that it is the speed of light!!)
5. Distance to boundary = v x t x 0.5
6. The division by 2 is needed as the t is the time for the whole journey of the wave to the boundary and back so the distance needs to be halved to find the distance to the boundary
37
What two characteristics does a pulse need to have to make high resolution images and why?
Short pulse duration - to limit wave interference
Short wavelength/high frequency - to minimise diffraction and hence increase resolution
38
What is the limitation on the pulse length emitted to find the distance to an object/form an image of that object
The pulse length must be < the time taken for the pulse to return to the emitter (which is 2 x distance to the object /wave speed)
39
What is diffraction?
The spreading out of waves as they pass an obstruction
40
What is phase?
Phase = how far through a wave cycle a given point on a wave is
41
What does it mean if two particles are in same phase
Particles in phase are an integer multiple of wavelengths apart (1 or 2 etc) (this is their path difference) and are always moving in the same direction
42
What does it mean if particles are in anti phase
Particles in anti phase are an integer multiple of wavelengths plus 1/2 a wavelength apart (path difference) and are always moving in opposite directions. They always have the opposite displacement to each other (one has the negative displacement of the other)
43
where on a wave are particles stationary and why?
Crests/troughs as all kinetic energy has been converted to potential energy so they are currently stationary (the derivative of the curve with respect to time is 0, and their velocity is 0)
44
How many radians in 360 degrees?
2pi
45
How many radians is one complete wave cycle for a thing going in a circle
2 pi (obvs)
46
How many radians apart are two particles in anti phase?
Pi radians (180 degrees) in other words - half a wavelength (as a wave, when split in half, has one side as the negative of the other!)
47
What does it mean for two waves to be coherent?
- they have same frequency, wavelength
- and their phase difference is constant
48
What is one interpretation of a (sinusoidal) wave graph which involves a circle
A graph of the vertical height of the radius line of a circle on the y axis against the angle of the radius vector on the x axis
49
What is the phase difference between 2 waves?
*The difference in angle between the two wave cycles *
This definition needs to be improved!
50
What value (lambda or Time period) is invisible on a displacement distance graph?
Time period
51
Explain how a sound wave travels through the air
Oscillations of air particles
Direction of Oscillations are parallel to the direction of energy transfer
It is a longitudinal wave
52
What is equilibrium position
0 displacement (where a particle would be with no wave present)
53
In what circumstance is a wave mostly reflected from a boundary
When it passes a boundary with a very large difference in density between the two materials
54
What does changing volts/div change on an oscilloscope
The scale of the y axis (the voltage axis)
55
Explain how a sound wave travels through the air (3 marks)
Oscillations of air particles
Oscillations are parallel to the direction of energy transfer/propagation
It is a longitudinal wave
56
Define path difference
The difference in the distance travelled by two waves from their source to the position that they are received
57
Define phase difference and give 2 possible meanings of it in different contexts
Difference in phase between 2 points on a wave
(difference in phase between 2 particles or one particle at 2 different times)
58
Explain whether two waves in are in antiphase given that the wavelength is 10cm, and one wave emitter has been moved 5cm away from the other wave emitter
- The traces will be in anti phase (phase difference is pi radians)
- Because the path difference is half a wavelength
- (The microphones are 5cm apart which is one wavelength (10cm)/2) basically using evidence from question
59
What is the path difference between 2 points on a wave that are in phase?
N (a positive integer) x wavelength
60
What is the path difference between 2 points on a wave in anti phase?
N (a positive integer) x wavelength + (wavelength/2)
61
What is the difference between a metre rule and ruler?
A metre rule starts at 0!
62
What does a phase difference of pi/4 equal in terms of path difference and time difference
Lambda/8, T/8
63
Give an equation linking proportion of time period, phase, wavelength
Delta t/T = delta theta/2pi = delta s/lambda
64
Why can’t you measure path difference?
You measure the positions of sources/receivers - you then CALCULATE path difference
65
Explain how you would use (this) apparatus to measure the speed of sound in air:
- Measure the initial position of the microphone using the metre rule
- Move the microphone until the traces are next in anti-phase
- Calculate the distance moved by the microphone (path difference) = wavelength
- Determine the time period using the number of divisions of 1 full wave cycle x time base
- Wave speed = wavelength x 1/T
66
Explain how you would use (this) apparatus to measure the speed of sound in air:
- Measure the initial position of the microphone using the metre rule
- Move the microphone until the traces are next in anti-phase
- Calculate the distance moved by the microphone (path difference) = wavelength
- Determine the time period using the number of divisions of 1 full wave cycle x time base
- Wave speed = wavelength x 1/T
67
How do you find the phase difference on a displacement time graph?
Find the phase of each particle at t=0 and work out the difference
68
How do you find the phase difference on a displacement distance graph?
Find where 0 and pi are on the wave (by checking which direction is the future of the wave and hence the higher displacement) and then find the difference in phase at a point
69
Define accuracy
How close a measure value is to the true value
70
Define precision
How close REPEATED measurements are to each other/the mean (can’t be judged on just one data point)
71
How does random error affect results?
Lowers precision
72
How does random error affect results?
Lowers precision
73
How does systematic error affect measured results?
Lowers accuracy
74
How does systematic error affect measured results?
Lowers accuracy
75
Define random error
Error caused by factors that vary from one measurement to another (and therefore leads to results randomly spread around the true value and have a low precision)
76
Define systematic error
Error that causes all measurements to be different from the true value by the same value
77
Why do we repeat measurements?
Reduces the effect of random error
So the mean is more likely to be closer to the true value
78
Define uncertainty
The interval within which the true value is considered to lie with a given level of confidence or probability
79
How do you calculate absolute uncertainty for a single reading
Resolution /2
80
How do you calculate absolute uncertainty for repeated readings
Range of results/2
81
When a wave travels through a medium with a different density to the one previously, what two values change of these three: wave speed, frequency and wavelength and why?
Wave speed and wavelength, not frequency (as there is no Change in energy)
82
Give a 3 mark answer to a question asking about changes in the phase differences between two traces being measured by moving a source of wave apart from another one by half a wavelength
MP1 - the traces are in phase/describe the phase given
MP2 - as one detector moves there is a path difference
MP2 - the traces are then in antiphase (describe the phase given) as they have moved half a wavelength/(describe the change in wavelength) apart
83
Give the wavelength range of gamma rays
Less than 10^-12m
84
Give the wavelength range of x rays
1nm-1pm
85
Give the wavelength range of ultraviolet light
400nm-1nm
86
Give th wavelength range of visible light
750nm - 400nm
87
Give the wavelength range of near infrared light
2.5 micrometers - 750nm
88
Give the wavelength range of infrared light
25 micrometers - 2.5 micrometers
89
Give the wavelength range for microwaves
1mm - 25 micrometers
90
Give the wavelength range for radio waves
More than 1mm
91
Define wavefront
Line/surface connecting points in phase on adjacent waves
92
Define constructive interference
the superposition of two waves that are in phase, producing a larger amplitude resultant wave
93
Define destructive interference
the superposition effect of two waves that are out of phase, producing a smaller amplitude resultant wave
94
If there is a gap between a pointer on a dial and the scale - what type of error could occur? What will this introduce to the measurements?
Parallax error - uncertainty
95
If a piece of measuring equipment has a low resolution, does this lead to a low precision or high uncertainty?
High uncertainty NOT low precision
96
(3 marks) - explain why time between emitted pulses has to decrease as an animal using echolocation gets closer to theri prey
- the (animal) moves closer to the (prey) as pulses are emitted so the distance between pulse emissions decreases
- this means pulses may overlap
- making it hard for the bat to distinguish between pulses (3 marks)
## Footnote
see. diagnostic test Y12 for an example of this question
97
give the 3 common answers for the waves topic to check that you ahve answered when doing questions about waves:
- have you **multiplied** **by** **two** to find the time for a pulse to return after being sent
- is the pulse a light pulse? have you therefore stated that it is moving at the **speed** **of** **light**?
- is the question asking about whether you can **distinguish** **between** **pulses**/whether one wave will interfere with another, making pulses hard to distinguish(due to a pulse length that is too high or a time between emitted pulses that is too shortg? (it probably is)
98
99
Give the Exam definition for superposition
When two or more waves meet at a point, the resultant displacement is the vector sum of the individual displacements
100
Give the conditions for complete destructive superposition
Waves have same amplitude
Constant phase difference/same frequency (coherent)
In anti-phase
101
Give the condition for an observable fixed stationary interference pattern
Waves are coherent (same frequency and constant phase difference)
102
What are coherent waves?
Waves with the same frequency and constant phase difference
103
What creates a standing wave?
A travelling wave is reflected, and interference causes a standing wave to be created
104
What causes nodes to be made?
Destructive interference
105
What causes anti nodes to be made
Constructive interference
106
When is a stationary wave formed (this is the same as a standing wave)
When two waves travelling in opposite directions interfere
107
What are the 3 conditions for a standing wave to form
The two waves must have the same speed, frequency and amplitude (or nearly equal amplitude)
108
Give an example of a standing wave in practice
A standing wave on a stringed instrument
109
What is a node
A position of 0 amplitude
110
What is an anti node
Position of maximum amplitude
111
What is the phase relationship between particles in one loop
All particles in one loop are in phase (as they are all moving up or down at the same time (as the loop is essentially oscillating up and down))
112
What is the phase relationship between particles in adjacent loops
All particles in one loop are exactly out of phase with all particles in the adjacent loop (as the particles in one loop reach maximum positive amplitude when the particles in the next are at lowest amplitude)
113
For a stationary wave on a string, both ends need to be what and why
Nodes - the ends cannot move
114
What is the distance between two adjacent nodes/antinodes
Half a wavelength
115
What is the first harmonic/fundamental frequency?
A standing wave with a wavelength equal to twice the length of the string
116
What is the relationship between the frequency of the second harmonic and first harmonic (fundamental frequency)
2nd harmonic frequency is twice the fundamental frequency
117
What is the relationship between the wavelength f the 2nd and first harmonics
2nd harmonic’s wavelength is half the 1st harmonic’s
118
Give the 3 ways to increase the pitch of a note played by a guitar
(Increase the frequency) and therefore:
- shorten the string by holding it down
- decrease the mass per unit length by making the string thinner
- increase the tension by pulling the string tighter
119
Antinodes are how far between nodes
Midway
120
The displacement is greatest at nodes/antinodes
Antinodes
121
The displacement is zero at ___in a standing wave
Nodes
122
What is one common example of creating a standing wave
A wave interferes with its own reflection in a stringed/woodwind instrument
123
When one end of a stretched string is vibrated, what happens? (4 bullet points)
- a travelling wave moves along the string
- Reflects from the other end
- then the wave interferes with its own reflection
- creating a stationary wave
124
What is the wavelength and frequency of the third harmonic? How do you know this?
The wavelength is 2/3 times the length of the wave (as there are 3 peaks between the fixed points, and 2 peaks constitute a wave, so there are 1.5 waves in the length of the string, so the length of one wave is 2/3 times that which is 2/3Length of string)
Teh frequency is 3 times the fundamental frequency as frequency is wave speed/wavelength, and as wave speed is constant for both (since the wave is a reflection of itself), the speedx3/2 as a ratio to the speed x 1/2 is 1:3, so the frequency is x 3)
125
How do you calculate the wavelength of. Standing wave if you know the length of the string and the number of loops
Wavelength is length of two loops
So the wavelength is length of the string divided by numb er of loops x 2
126
Describe how you would force a string to vibrate at a particular frequency, including mentioning all the equipment you would use
Use a pulley and weight attached to one end of a string, and a signal generator and vibration generator attached to the other end
127
What is the equation for the speed of a standing wave?
V = root the (tension in the string divided by mu) where mu is the mass per unit length
128
What is the wavelength of a standing wave on a string with a node at both ends
2 x length of the string
129
There must be a __or a ___at both ends of a standing wave
Node or anti node
130
At a node, the particle is not ___to oscillate (either due to the superposition of two waves or a physical constriction determining the movements of that particle)
Free
131
Wavelength and frequency are in ___proportion with a fixed wave speed
Inverse
132
When you have a pipe that is open at one side, the standing wave is bounded by a ___on one side and a ___on the other side
Node, anti node (anti node is at the open end)
133
Why is the wave reflected at the end of an open ended pipe
There is a change in pressure, causing a partial reflection of a wave (high pressure inside the pipe, lower pressure outside the pipe)
134
Give an example of a standing wave in a pipe that is open on one end
Waves in reed instruments like an oboe, saxophone, clarinet
135
When you have a pipe with one end closed, what harmonics can be achieved and which cant and why?
Only odd harmonics can be achieved as it is a node at one end and an anti node at the other end
136
What is the frequency of the 5th harmonic in terms of the fundamental frequency (always)
5 x frequency of the fundamental
137
What is the wavelength of the 5th harmonic in a pipe with one end closed
4/5 x length of the pipe
138
In a pipe with two open ends, which harmonics can be obtained and why?
All harmonics, as it is bounded by two anti nodes
139
A standing wave in a two side open ended pipe is bounded by two nodes/antinodes
Antinodes
140
What is the wavelength of the third harmonic in a pipe with 2 open ends
2/3 x length of the pipe
141
What is the phase difference on a travelling wave between two particles in terms of their path difference
Path difference/wavelength x 2 pi
142
Are the amplitudes of A and B on a travelling wave the same or different?
The same
143
True or false: you can express phase difference as a fraction
False - it must be as an angle (pi/2 or 90 degrees)
144
In a standing wave, all particles separated by __or an even/odd number of nodes are in phase
Even, 0
145
All particles in antiphase with each other on a standing wave are separated by how many nodes
An odd number
146
In a standing wave, the amplitude is the Same/different for all particles
Different
147
What is the position of maximum, maximum displacement in a standing wave called? What is a better description of this?
Antinode - position of maximum amplitude
It is the position of maximum maximum displacement as each particle has different maximum displacements/amplitudes,
148
True or false: standing waves transfer energy
False
149
What is superposition
When two or more waves meet at a point the resultant displacement is the vector sum of the individual displacements
150
True or false - interference and superposition are the same thing
False - superposition is the general term for two waves meeting and interference is a specific term for when two coherent waves meet to create a wave with a constant frequency and amplitude following the interference
151
In a standing wave there is no___transfer in any specific direction
Energy
152
If you had a signal generator which vibrates air particles over a flat pile of sand, where will the sand collect in piles and why?
At the nodes.- as the air molecules have 0 amplitude at these positions so they dont disrupt the sand, but at the anti nodes, air molecules oscillate with maximum amplitude and disrupt the sand
153
What is the distance from one node to the next node
Wavelength / 2
154
Do nodes have a phase
No
155
Compare the properties of the sound wave to cancel out a sound wave into a headphone versus the wave produced to cancel it out
Sound waves must be in anti phase
They must have the same amplitude
And frequency
156
Why do noise cancelling headphones find it hard to cancel out the sound of human speech? (3 marks)
Noise of vibrating object has a more constant frequency and amplitude
Frequencies and amplitudes in speech vary
As the signal from speech varies a lot you would need a very high sampling rate to detect and produce a new wave that cancels the speech quickly enough - this would be difficult to achieve
157
Exam question on phase difference in interferometer:
Without the gravitational waves, the waves arrive in anti phase
Resulting in destructive interference
And 0 amplitude
When there is a change in the length of one arm, the path difference would change - leading to, for example, the waves arriving in phases with constructive interference and a bright signal with a non-zero amplitude
158
Why is the interferometer set up to have a 0 amplitude wave at the photodetector at the start?
Generally - the most sensitive way to detect something is by starting at 0
- Because the % change from 0 to anything is very very large (infinite)
159
Why is the interferometer set up to have a 0 amplitude wave at the photodetector at the start?
- Because the % change from 0 to anything is very very large (infinite)
160
What is white light
all wavelengths of visible light are present
161
explain phase difference in an interferometer (how it happens)
Without the gravitational waves, the waves arrive in anti phase
Resulting in destructive interference
And 0 amplitude
When there is a change in the length of one arm, the path difference would change - leading to, for example, the waves arriving in phases with constructive interference and a bright signal with a non-zero amplitude
162
What is wavelength of blue light
400nm
163
what is wavelength of red light
700nm
164
What is the path difference of two rays: one of which has reflected from the back of a thin film, and one that has reflected from the front?
2 x the distance from the inside to the outside of the film
165
the thickness of a bubble is uniform/non-uniform
non-uniform - it is thicker at the top and bottom
166
explain why a certain part of the bubble appears blue
the orange light is destructively interfering
As the orange wavelength light has a path difference that causes it to meet in anti phase
Resulting in zero amplitude orange light
The blue light is constructively interfering
As the blue wavelength light has a path difference that causes it to meet in phase
Resulting in maximum amplitude blue light
The white light thus has orange wavelengths removed and blue wavelengths have higher intensity
167
when you have a wave that reflects from a denser mediumm, what happens to the phase
it increases by pi
168
in questions about phase/path difference how should you describe the path difference required for anti phase? Phase?
(N+1/2)lambda or nlambda
169
always link back to key ___in the question
words
170

171
After diffraction, what 3 things dont change
wavelength, wave speed and frequency
172
what is a wavefront
a line/surface connecting POINTS that are IN PHASE on ADJACENT WAVES
173
What is teh distance between consecutive wavefronts
one wavelength
174
what is diffraction
the spreading out of wavefronts as they pass through a gap or around an obstacle
175
state huygen’s construction
each point on a wavefront acts as a source of secondary circular wavelets
The wavelets undergo superposition when they meet
This produces a new wavefront that is the surface tangential to the secondary wavelets
176
What does huygen’s construction not explain
why these phenomena occur from a mathematical standpoint
177
the radius of the secondary circular wavelet should be equal to ___when there is part of the diffracted wave that is straight and parallel to the gap
the wavelength
178
when drawing a diagram for huygen’s construction in an exam you must use what top ensure the radius of wavelet = ?
ruler
Wavelength
179
what type of waves diffraction more?
longer wavelengths
180
why are radio waves used for communication
they have longer wavelengths and so diffract more (they can pass around obstacles like hills more easily
181
small gap size creates diffracted waves that are more/less curved and why
more - when wavelength equals gap size then maximum diffraction effects occur
It’s because there are fewer points on the wave emitting wavelets (so the area of the diffracted wave parallel to the gap is equal to the gap size but the gap size is much smaller so it just appears rounded)
182
teh straight part of the diffracted wavefront has minimal/maximal diffraction effects
minimal (diffraction is the curving of the wavefront)
183
in cases where the gap for waves to diffract through is very very small (in comparison to the wavelength of the wave) what happens to the diffracted wave
it has very low intensity
184
what are two characteristics of maximum diffraction of a wave and when does this occur
maximum curvature and maximum amplitude of diffracted wave
When the gap size equals the wavelength
185
186
Give the general form for phase difference for constructive interference
2pi n (where n is an integer)
187
Explain why two waves could completely destructively interfere and still not create a 0 amplitude wave
If one wave has travelled further than the others
It’s energy has spread out (dissipated but dont say the word dissipated) more
So it has a lower amplitude
So even if they have complete destructive interference and are coherent the amplitude of the resultant wave will not be 0
188
If light is not monochromatic (for example if it is white light) it doesn’t have a constant what
Frequency
189
Why can interference and diffraction only happen to a wave not a particle
particles cant show destructive interference
Particles cant spread out (in diffraction)
190
what damage can lasers do
damage retina if directed at eyes
191
what does lower case d denote
slit separation in diffraction grating
192
What is D in the diffraction grating practical?
Slit screen distance
193
what is the value x in the diffraction grating practical
distance from central maxima to nth order maxima
194
what is the value x measured with
a metre rule or vernier calliper
195
what is the maximum distance a vernier calliper can measure
15 cm
196
what is the resolution of a vernier calliper
0.1mm
197
what is D measured with in the slit experiment
a metre rule/tape measure
198
tan theta = what in the slit experiment
x/D
199
if the angle theta is small (if x/D is small) then what does the equation dsin(theta) = n x lambda become? why?
the small angle approximation for tan theta and sin theta is theta, so theta becomes equal to x/D
so the equation becomes dx/D = nlambda
200
can you use small angle approximations when using a diffraction grating? why/why not?
- no as the slits are too close together, which means the value of x can be much higher, so theta isn't small enough
201
theta (angle between the normal and the light ray heading to the point of convergence) can be treated as equal for different light rays - why?
- as D becomes very large they can be treated as equal
202
derive why tan(x/D) = theta
and also derive sin(theta) d = n lambda using the same diagram
treat the two light rays as parallel
then draw a triangle to show the path difference between the light rays
then use the fact that the line of the triangle between the parallel lines to find the path difference must be at a right angle to the light ray to find that the path difference is equal to sin(theta) x d
and we know the path difference can also be expressed as n lambda
so sin(theta) d = n lambda
203
explain why diagrams used to model the slit experiment are not to scale
x is much much smaller than D which the diagram doesn't show
and d is much smaller than x
and d is much smaller than D
204
what two things could be used to measure D
a tape measure or metre rule
205
what is the angle theta
angle between central maxima and nth order maxima
206
in the sin(theta) d = n lambda equation can n be any real number or does it need to be an integer
integer - as the light rays you measure are converging to a maximum so constructive interference needs to happen, and given they are in phase at the start (as from same source) they should be in phase during the path difference as well
207
why does the light source need to be perpendicular to the screen
he light source needs to be perpendicular so that the waves arrive in phase
- The fact that they are perpendicular means that the path difference is 0 as the path length for all waves is the same
- This ensures they will arrive in phase
208
why should the laser beam be monochromatic
otherwise white light would have multiple different maxima for different colours (as they have different wavelengths)
209
how can you improve the accuracy of the experiment when setting up the diffraction grating and meauring D (give 2 things)
Check the diffraction grating is perpendicular using the set square in all 360 degree directions!!
Also use the set square to ensure the metre rule for measuring D is perpendicular
210
how can you reduce uncertainty in measurements of x(give two possible ways)
Measure the distance (x) from the nth order to the same n on the other side and then divide by 2
- This is to reduce % uncertainty
- Which increases likelihood of accuracy
- Note when you are explaining this you have to say:
○ Increasing measurement size to determine x
○ State the equation for % uncertainty in x
○ And absolute uncertainty is a constant
Or you could measure the distance form the nth order maxima to the central maxima, and then the n’ th order maxima on the other side
- By repeating you reduce the effect of random error
- So the mean is closer to the true value
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how does the use of vernier callipers affect measurements of x
- increases resolution
- leading to lower absolute uncertainty in measurements of x
212
what does increasing the grating screen distance (D) do for measurements of D and x
- Increases D, lowering % uncertainty for D
- Increases x, lowering % uncerinaty for x
- But the limit is 15 cm for x as you need a vernier calliper
213
how do you check for 0 error on the vernier calliper
check the reading with the jaws closed before completing the measurement
214
what is the minimum resolution of a vernier calliper
0.1mm
215
how do you read a vernier calliper
Read main scale (to find the large interval that the reading lies within)
Then read vernier scale and add on the distance from 0 on the vernier to x on the vernier scale where x lines up with a line on the main scale
Then add the main scale reading to the vernier
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label a micrometer
