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115 Cards in this Set
- Front
- Back
- 3rd side (hint)
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What are progressive waves? |
Waves that transfer energy without transferring matter. |
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Name 2 types of progressive waves. |
Transverse waves Longitudinal waves |
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What are transverse waves?
Give examples of transverse waves. Draw a visual representation of a transverse wave. |
Waves where the displacement is perpendicular to the direction of the wave. E.g. Electromagnetic waves, water waves, waves on a string, Seismic S(Secondary Waves) which are waves in the earth.
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What are longitudinal waves? Give examples of longitudinal waves. Draw a visual representation of longitudinal waves, labelling any important parts. |
Waves where the displacement is parallel to the direction of the wave, causing areas of compression and rarefaction to form. E.g. Sound waves, Seismic P(Primary) waves |
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In a longitudinal wave, Points on the wave that are 1(lambda) or wavelength away from each other move in what direction relative to each other? Points on the wave that are ½(lambda) or wavelength away from each other move in what direction relative to each other? |
1 lambda (wavelength) away, they move in the same direction. ½ lambda away, they move in opposite directions to each other. |
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Draw a transverse wave, and label all important parts. |
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What is the definition of the amplitude of a transverse wave? |
The maximum displacement from the line of equilibrium to the crest/trough of a wave. |
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What is the wavelength of a transverse wave? |
The distance between 2 crests or 2 troughs. |
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What is frequency? What is the unit for frequency? |
The total number of complete waves passing a single point per second. Measured in Hz (hertz) |
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What is the equation for the speed of a wave? |
V is speed F is frequency Lambda is wavelength. |
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v = f(lambda) So if speed were to remain constant, what would happen to lambda if f increased? Desmonstrate what would happen to lambda if f increased by x2. |
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What are the 2 properties that all electromagnetic waves have in common? |
They all travel at light speed They can all travel through a vacuum. |
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What is polarisation? |
The process of making a transverse wave oscillate in only one plane (one orientation) (up, down, left, right, diagonal etc) |
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Draw a situation where an incident wave is 90° to a wave filter, show what will happen and explain why it happened. |
Nothing will come out from the other side of the filter. This is because the filter is 90° to the wave's orientation, so the wave will be completely blocked out. |
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Draw a situation where an incident wave has the same orientation as the wave filter, explain what will happen and explain why it will happen. |
The wave will go straight through since the filter has the same orientation as the wave. |
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Waves can move in multiple planes. What can wave filters do to waves that move in multiple planes? |
The filters can stop parts of the wave with certain orientations from passing through. |
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Where is polarisation used? |
Polarisation is used in sunglasses. |
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Explain how polarisation is used in sunglasses.
Draw a diagram as well. |
Sun rays can reflect off the water and get polarised.
The filters in the sunglasses may have an opposite orientation to the polarised sun rays, so the sun rays will be blocked out. |
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What is the time period of a wave? What is the equation and units for time period? |
The time it takes for a wave to complete a full cycle. |
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The cycle of a wave can be measured in radians, where 2(pi) radians = 360°. How many radians represents: 1) A full cycle? 2) a half cycle? 3) a quarter cycle? |
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When are 2 points on a wave completely in phase?
Draw a diagram to show 2 points complrtely in phase. |
2 points on a wave are completely in phase if they are on the same part of a wave (1 wavelength away from each other)
On the diagram, the two dots are in phase with each other. |
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When are 2 points on a wave completely out of phase? Draw a diagram to show 2 points completely out of phase. |
2 points on a wave are completely out of phase when they are (pi) radians out of phase (or out of phase by ½ a wavelength.) On the diagram, the 2 dots are completely out of phase. |
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Draw a diagram where 2 points on a wave are ½(pi) radians out of phase (out of phase by ¼ a wavelength) |
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What is phase difference?
What is the equation for phase difference? What is the unit for phase difference? |
How out of phase 2 points on a wave are.
d is distance between the two points Unit for phase difference is radians. |
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Under what circumstance can you find the phase difference between 2 points that aren't on the same wave? |
When the 2 points are on waves with the same wavelengths as each other. |
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What does it mean when 2 waves are coherent? |
The 2 waves have a constant phase difference (the phase difference between the two waves remains the same) |
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What is superposition? |
When 2 waves meet at the same point at the same time, causing them to undergo constructive interference (amplitudes add) or destructive interference (amplitudes subtract). |
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Explain what happens in constructive interference and Draw a diagram to demonstrate this. |
The amplitudes of the two waves add up since they are completely in phase. |
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Explain what happens in destructive interference and draw a digram to demonstrate this. |
The amplitudes subtract since the waves are completely out of phase. |
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What is a stationary wave? |
A wave that stores energy and is formed as a result of superposition when 2 progressive waves of the same frequency and wavelength travel through each other. |
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Draw what a stationary wave looks like. What does a stationary wave do? |
It doesn't move. The peaks and troughs of the wave just move up and down. |
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Describe how a stationary wave is formed in practice. Draw a diagram to demonstrate this. |
A progressive wave is fired at a fixed end, reflects from the fixed end and the reflected wave interacts with the initial wave. This causes constructive interference to occur at the anti-nodes, and destructive interference to occur at the nodes. |
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Define interference. |
The formation of points of cancellation and reinforcement when 2 coherent waves pass through each other. |
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What is the equation to calculate the phase difference between two points on a stationary wave? What is the unit for phase difference? |
m is the number of nodes between the points being compared. Unit is radians.
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In stationary waves, what do all of the points between two nodes have in common? |
They are all in phase with each other. |
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Where are the nodes and anti-nodes on a stationary wave? What are nodes? What are anti-nodes? |
Nodes are fixed points on a stationary wave that remain in the same place. Anti-nodes are fixed points on a stationary wave where the amplitude/displacement from equilibrium is maximum. |
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There are different types of stationary waves. What do we call them? |
Harmonics |
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Draw what the first harmonic would look like. What is the length of the harmonic in terms of lambda(wavelength)? What is the frequency of the first harmonic also known as? |
Length of 1st harmonic = ½(lambda)
(Since only half a wavelength forms) The frequency of the first harmonic is known as the fundamental frequency. |
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Does v = f x lambda Still apply to harmonics? How would you find the lambda(wavelength) of the harmonic to put into the v equation (if the actual length of the harmonic was given to you)? |
Yes. To find the wavelength of a givern harmonic, write the length in terms of lambda(wavelength), equate it to the given length and solve for lambda. |
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Draw what the 2nd harmonic would look like.
What is the length of the 2nd harmonic in terms of lambda? |
Length = lambda |
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Draw what the 3rd harmonic would look like.
What is the length of the 3rd harmonic in terms of lambda? |
Length = 3/2(lambda) |
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What is the general equation to find the length of any harmonic, represented by the letter n, in terms of lambda? Under what circumstance can this equation be used? |
n = number of anti-nodes OR Harmonic number. Ln = length of nth harmonic. This equation can be used when there are nodes at BOTH ENDS of the stationary wave. |
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Besides v = f x lambda,
What is the equation used to calculate the frequency of any harmonic, represented by the letter n ? |
Fundamental frequency is the frequency of the 1st harmonic. |
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In harmonics, what is the same as the harmonic number? |
The number of anti-nodes in that harmonic. |
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Stationary waves may be given to you in an incomplete state. An example is the one in the picture. What is the length of this stationary wave in terms of wavelength? |
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What is the length of this stationary wave in terms of wavelength? |
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What is the length of this stationary wave in terms of wavelength? |
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What is the length of this stationary wave in terms of wavelength? |
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What is the equation used to calculate the fundamental frequency of a given string (frequency of 1st harmonic)? State what each part of the equation means as well. |
L is length of string T is tension in the string (force being applied to the string) Mew is mass per unit length (kg/m OR p(density) x A(cross-sectional area). Bassically mass per metre. |
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What is the relationship between the fundamental frequency of a string and the string's tension? |
Fundamental frequency is directly proportional to the square root of the tension. |
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If the tension of a string increased by x4, how much would the frequency increase by? (Use the equation for the fundamental frequency to help you.) |
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What is diffraction? Draw a visual demonstration of diffraction. |
The spreading out of waves when they go through a gap. |
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What does diffraction prove about light? |
It proves that light can act as a wave. |
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Someone named 'Young' came up with an experiment to demonstrate the wave nature of light. This will come to be known as Young's double slit experiment. Explain how it was originally done and explain why the first stage was done. Draw a diagram to demonstrate the original Young's double slit experiment. |
1) Young lit a candle and the light from it would be sent through a single slit, causing it to diffract. He sent the light through a single slit first so he could get monochromatic and coherent light to come out of the double slits. 2) The diffracted light would diffract again through the double slits, causing them to form bright and dark fringes on the screen through constructive and destructive interference. |
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What is monochromatic light? |
Light of a single wavelength. |
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What does it mean if two or more waves are coherent? |
They have a constant phase difference. |
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If light has a longer wavelength, does it diffract more or less? If light has a shorter wavelength, does it diffract more or less? What colour represents: The longest wavelength of light The shortest wavelength of light? |
Longer wavelength - diffracts more Shorter wavelength - diffracts less. Red represents the longest wavelength of light Violet represents the shortest wavelength of light. |
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What is the acronym used to represent the colours of the different wavelengths of light? Does it go from longest wavelength to shortest or shortest wavelength to longest? |
ROYGBIV. Longest wavelength to shortest. |
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Draw a visual demonstration of a modern day Young's double slit experiment. For Young's double slit experiment, what do we do differently nowadays compared to the original experiment and why? |
We just use a laser instead of a candle and a prior single slit because lasers produce coherent, monochromatic light. |
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In the modern day Young's double slit experiment, what colour laser is usually used? (NOTE: IT ISN'T USED ALL THE TIME) |
Red laser light is usually used. |
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In the Young's double slit experiment, when the diffracted light from the double slits hits the screen, fringes of light are formed on the screen. What two processes are occuring between the diffracted lights from the double slits, allowing this to happen? |
Interference Superposition. |
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In Young's double slit, light waves meet a different parts of the screen along a straight line. Draw a demonstration of young's double slit for light waves that meet at the centre of the screen.
Label every part of relevance and their meanings,
state the kind of fringe that forms,
what kind of interference occurs and why,
What the path difference between the two light waves is and why their path difference is this value. |
S is slit separation (distance between the centres of both slits)
D is distance between the double slit and the screen
Bright fringe forms.
Path difference = 0 because both light waves have travelled the same distance to get to the same point.
Constructive interference occurs because their path difference is 0. |
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When is the diffraction of a wave greatest? |
When the wavelength of the wave is the same size as the gap the wave is going through. |
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Draw an example of Young's double slit for waves that have a path difference of n(lambda), where n is a positive integer.
What kind of fringe forms and what kind of interference occurs?
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A bright fringe forms.
Constructive interference occurs. |
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In Young's double slit, how can you find the actual value of the path difference between two waves that don't meet at the centre of the screen? |
Path difference = distance from (the middle of the slit producing the less angled wave)
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(the perpendicular of the wave from the slit producing the more angled wave) |
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What is the general expression of the path difference between two waves that don't meet at the centre of the screen but form a bright fringe? |
n(lambda) Where n is a positive integer. |
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How can you find the path difference of two (destructively interfering) waves that meet between two pairs of waves that both undergo constructive interference? (Using the path differences of the constructive interference waves) |
(greater path difference - smaller path difference) ÷ 2 + Smaller path difference. |
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In diffraction: If you decrease the gap size, what happens to diffraction? What can you decrease the gap size down to, why is this gap size important, and what happens if the gap size gets smaller than this? |
Diffraction increases. You can decrease the gap size down to lambda (wavelength) and that's where diffraction is max. If the gap is smaller than the wavelength, the waves mostly reflect back. |
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In diffraction, If the gap size is ALOT bigger than the wavelength of the wave, is diffraction still happening, and how much is happening? |
If the gap is alot bigger than lambda, diffaction is still happening, but it's virtually unnoticeable. Barely any diffraction is happening. |
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Prove algebraically that diffraction can't happen if the gap size is below lambda. |
Use the diffraction grating equation n(lambda) = dsin(theta) (d is the width of one slit, so basically one gap) For 1 diffraction, n=1 so (Lambda/d) = sin(theta) If lambda>d, sin(theta) = a value above 1, and sin(theta) is undefined for y values above 1 and below -1. |
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Waves are represented like this when talking about diffraction. Label what part of the wave is the wavelength. |
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For a given gap, What will happen to diffraction if the wavelength is: Bigger Smaller? |
Bigger wavelength, more diffraction Smaller wavelength, less diffraction |
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Draw a visual example of multiple waves of path differences on one diagram. Label every part of significance.
(Draw the diagram for waves with path differences between and including 0 and lambda) |
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At every n(lambda) path difference, what kind of interference occurs? At every ½n(lambda) path difference, what kind of interference occurs? |
n(lambda) path difference: constructive interference occurs. ½n(lambda) path difference: destructive interference occurs. |
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What is fringe separation?
What is the equation to calculate fringe separation? |
The distance between two bright fringes.
w is fringe separation Lambda is wavelength D distance between double slit and screen s is slit separation (distance between the double slits) |
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1) What is the relationship between w(fringe separation) and s(slit separation) in terms of proportionality?
If s were to rise by x2, what will happen to w?
2) What is the relationship between w(fringe separation) and D(distance between double slit and screen) in terms of proportionality? If D were to rise by x2, what will happen to w? |
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What is white light?
If white light was to diffract through a single gap, describe what would be seen.
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Light with multiple wavelengths.
Different wavelengths will diffract by different amounts. Red will diffract the most since it has the longest wavelength Violet diffracts the least since it has the shortest wavelength. |
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Draw an interference pattern for a double slit. Label the y-axis correctly as well. |
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Draw an interference pattern for a single slit. What are the features of a single slit interference pattern? |
.The central maximum (middle fringe) is very bright compared to the other fringes . The central maximum is double the width of the other fringes. |
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In a diffraction grating, instead of having two slits like a double slit, how many slits does a diffraction grating have? (Not a specific number) |
A diffraction grating has many slits. |
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Draw an example of a diffraction grating from the 0th order to the 2nd order. (Theta) represents an angle can be measured from the 0th order to an nth order. What does (Theta) depend on? |
(Theta) depends on what order is being compared with the 0th order. |
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What is the equation used to calculate (nth order number) x (wavelength) in a diffraction grating?
(What is that equation used with diffraction gratings, don't know how else to describe it.)
State the unit of each component and what that component represents. |
n is nth order number
Lambda is wavelength (m)
d is slit width or grating spacing (distance between two slits in the diffraction grating) (m)
(Theta) is angle between 0th order and nth order. (°) |
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'D' in young's double slit represents the distance between the double slits and the screen.
What does 'D' represent in diffraction grating?
How can you calculate a diffraction grating's grating spacing/slit width (d) using D? |
For diffraction grating: 'D' = how many slits there are per mm.
d (unit metres, m) = (1/D) x 10^-3 |
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Practice question: A diffraction grating has 100 lines per mm. Find the slit width of the grating in: Metres Millimetres. Which of these two units does slit width (d) usually needed to be in? |
Metres: (1/100) x 10^-3 = 1 x 10^-5m Millimetres: just don't multiply by 10^-3. (1/100) = 0.01mm Slit width is usually needed in metres. |
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Practice question: a) A diffraction grating has 100 lines per mm, and the 2nd wave order is at 50° to the 0th order. Find the wavelength of the light.
b) Find the maximum number of orders that the light can have. |
a) D = 100 (Theta) = 50° d = (1/100) x 10^-3 = 1x10^-5m n = 2
Lambda = (d x sin(Theta)) / n = ((1 x 10^-5) x sin50) / 2
Lambda = 3.83 x 10^-6m
b) Basically, find 'n' at 90°. The orders can't go beyond a 90° angle. n(3.83 x 10^-6) = (1 x 10^-5) x sin90 Solve for n. n = (1 x 10^-5 x sin90) ÷ (3.83 x 10^-6) = 2.6 orders. Round down since 3rd order would exceed 90°. Max n = 2 orders. |
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Define refraction. |
The change in speed and direction of a wave as it enters a new medium (the thing that the wave is travelling in). |
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What is the speed of light in a vacuum? What is the speed of light in water? |
Vacuum: 3 x 10^8 ms^-1 Water: ¾(3 x 10^8) ms^-1 |
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As a wave enters a more dense medium what happens to it's wavelength, speed and frequency? |
Wavelength falls, Speed falls, Frequency stays the same |
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Draw a wave going from air to water at a 90° angle to the medium, and explain what is happening. |
the wave hits the boundary at 90°, so it will move in the same direction, but the wavelength and speed will still fall. |
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Draw a demonstration of refraction using wavefronts. |
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If a light were to shine onto a rectangular surface at an angle, label: The angle of incidence Angle of refraction The normal Any 90° angles of relevance Angle of emergence. |
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Angle of incidence and angle of emergence are what? |
Equal. |
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The normal is always perpendicular to what? |
The point of incidence / emergence. |
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If we have a equilateral triangular medium, and light is shone at it diagonally upwards, label: The angle of incidence The angle of refraction The normal The angle of emergence |
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Define refractive index (of a substance)
What is the symbol used to represent refractive index? |
The ratio of how much slower light travels in a medium compared to in a vacuum / in air. (Basically how optically dense a material is)
Represented by n. |
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What equation can be used to find the refractive index of a medium, using the speed of light in a vacuum and the speed of light in that medium? State what each part of the equation represents.
Under what circumstance can this equation be used? |
ONLY works when light moves from a vacuum/air into a more dense medium. |
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A substance has a refractive index of 1.5. Find the speed of light in that substance If light goes from air to that substance. |
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What does mean if a substance has a higher refractive index? |
It's more optically dense, so light travels slower in that substance. |
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What is the acronym that must be used when visually representing refraction?
What does this acronym state/stand for?
NOTE: USE THIS ACRONYM WHEN DRAWING REFRACTION! |
TAGAGA rule
Talking about light rays:
Towards (normal) if going from Air to Glass.
Away (from normal) if going from Glass to Air
NOTE: Air can be replaced with a less dense medium and Glass could be replaced with a more dense medium.
NOTE: USE THIS ACRONYM WHEN DRAWING REFRACTION! |
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How can you find the refractive index of a medium using the angle of Incidence and angle of refraction? (The light is travelling from a vacuum/air to a more dense medium) |
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What is the refractive index of a vacuum? What is the refractive index of air? Why can we make this approximation for the refractive index of air? |
Refractive index of air = 1 We can make the approximation that the refractive index of air is 1 since the speed of light in air is only slightly smaller than the speed of light in a vacuum. |
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Snell's law is used when refraction of light occurs between ANY two mediums.
What is the Snell's law equation? State what each part of the equation means. |
n↓1 is refractive index of 1st substance
(Theta)i is angle of incidence
n↓2 is refractive index of 2nd substance.
(Theta)r is angle of refraction |
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Draw an example of refraction occuring between any 2 mediums. Label any part of importance or relevance. |
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What is Total internal reflection? |
The complete reflection of a light ray after it hits a less dense medium at an angle of incidence greater than the critical angle. |
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What are the two condition that must be met for Total Internal Reflection to occur? |
1) The angle of incidence must be greater (>) than the critical angle 2) n↓1 > n↓2. The light ray must move from a medium with a higher refractive index to a medium with a lower refractive index. (The light ray must move from a more optically dense medium to a less optically dense one.) |
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Describe the stages of total internal reflection, with diagrams. (Stages 1 and 2 are on the hint flashcard) |
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What is the equation used to calculate the critical angle? (Use Snell's law.) |
n↓1 x sin(Theta↓c) = n↓2 x sin(90) Or sin(Theta↓c) = n↓2 / n↓1 When simplified (on eqn sheet)
Sin(90) is used as the angle of refraction since when the angle of incidence equals the critical angle, the angle of refraction is 90°. (See the diagram showing the total internal reflection stages.) |
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Give one use of Total internal reflection. |
Optic fibres. |
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Draw the common structure of an optic fibre and label each part.
(For the refractive indexes, you don't need to give exact numbers. Just label which part would have to greater refractive index and which part would have to lower refractive index.) |
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In optic fibres, what is the purpose of the protective sheath? |
To protect the optic fibre. |
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In optic fibres, what are the 2 purposes of the cladding? (1 purpose is just on its own and thd other purpose relies on the glass core as well) |
The cladding protects the core. It helps to create the conditions needed for TIR to occur. The glass core has a higher (>) 'n' than the cladding, allowing TIR to occur and for the light to travel great distances. |
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What is the purpose of optic cables? (Optic cables use optic fibres.) |
Multiplex. (Sending different wavelengths of light down the same cable.) |
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What are the 3 pros of having a cladding around an optic fibre? |
Protects the core Prevents loss of information Increases the rate of data transfer. |
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What are the 3 pros of having a smaller diameter glass core in an optic fibre? |
Less light is lost Quality of data transfer rises Less multipath dispersion (Light rays taking longer to go from one end of an optic fibre to another, causing its pulse to be stretched more at the end than when it was sent) |
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Draw a visual demonstration of multipath dispersion.
Describe what is happening. |
The black line took the shortest route from one end to the other.
The red line took a longer route, so its pulse at the end will be more stretched than its pulse at the start. |
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