Physics- Unit 2- Waves

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• Created by: FireDwarf
• Created on: 05-03-14 20:45
What are mechanical waves?
Wave that progresses through a substance and causes the particles of that substance to vibrate in a certian way.
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Electromagnetic?
vibrating electric and magnetic fields that progress through space without need for substance.
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What is a transverse wave? Whats the opposite? Definition?
When the vibrations of the wave are perpendicular to the direction of the wave. Longitudal- when the vibrations of W are parrallel to the D of wave.
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What is polarisation?
When the vibrations of the wave now stay in one plane only.
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What is an unpolarised wave?
A wave where the vibrations of the wave change from one plane to another.
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How do we polarise waves?
we can polarise waves by using a polaroid filter. The filter only allows vibrations parrerell to the slit to pass through it.
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What if we stick another plate behind it which is at a angle (eg: 90,270)
Light intensity will decrease because we are blocking waves passing through (no light at right angles).
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What is amplitude?
Maximum displacement of a vibrating particle (height of wave crest).
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How do we calculate wave speed?
Distance traveled in one cycle (which will be wavelengh) /time taken for one cycle (1/f)(speed = fx wavelengh).
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What does phase diffrence calculate?
Fraction of a cycle between the vibration of the two particles.
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Formula to calculate into radians?
2pied/wavelengh.
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What is reflection?
When a straight wave directed at a certian angle to a hard surfac reflects off at the same angle. The angle of incidence therefore equals the angle of reflection.
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Where do we take these angles from in comparrision?
The normal.
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What is refraction?
When a wave passes the boundary and its wave speed changes and as a result its direction also changes. (wavelengh also changes).
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When does it bend towRDs the normaL?
From rare to dense mediums.
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What is diffraction?
When waves spread out after passing through a gap or round an obstacle.
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diffraction occurs in the most when the gap is simualr to the wavelengh. Narrower gaps, more spread out. Longer wavelengh, more waves.
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What is the principle of super posistion?
When two waves meet, the total displacement of a point is equal to the sum of the individual displacements at that point.
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So what happens when a crest and crest meet? A trough and trough? A crest and trough?
Super crest, supertrough and zero because they cancel each other out.
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What is super trough and supercrest? What is when crest and trough meet?
Constructive interference & destructive interferance.
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How is a stationary wave formed?
When two progressive waves pass through each other.
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How can we achieve this?
Fixing a string in tension at both ends and making the middle part vibrate. Progressive waves travel towards each end, reflect and pass through each other.
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What is the node? What is an antinode?
A node is a point of no displacement, and a antinode is the posistion of where there is maximum amplitude.
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What is the distance between adjacent nodes?
Half of wavelengh.
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What do stationary waves do if they vibrate freely and why?
They do not transfer energy. This is because the amplitude at the nodes is zero so there is no energy at the nodes. Amplitude of vibration is maximum at the antinode so max energy is there. They are in fixed posistions so cant move.
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Why do stationary waves occur?
Because in one cycle they both reinforce and cancel each other out. In phase, they reiforce to produce larger wave 1/4 Later, out of phase, so cancel each other. Futher quarter, back in phase, larger wave but in reverse.
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Phase diffrence between two vibrating particles?
zero if two particles are between adjecent nodes or even number of nodes. `180 if odd number of nodes.
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What can we use microwaves to test for and why?
To test for superpostion. Place reciever in path of microwave beam. Move reciever away and should see signal decrease. Place metal plate between transmitter and reciever.
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conc
Use two metal plates to make slits to cause diffraction. Use narrow metal plate to make pair of slits. Where the waves meet, see if they cancel or reinforce each other.
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So how are the minima and maxima formed via super posistion when waves reflected?
Waves are getting reflected and as such as get a stationary wave. Where the crest and crest meet, we see them reinforce each other and produce a supercrest (maxima) which occurs at the antinode. The mnima is where they cancel each other, node.
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What can you produce?
diffrent stationary wave patterns as the frequency is increased.
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What are the three stationary patterns we will be looking at?
The fundermental (1st harmonic) , the first overtone (2nd harmonic), 2nd overtone (3rd harmonic).
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What is the fundermental? Node arrangement?
The pattern given at the lowest possible frequency. Antinode in middle, nodes at the end.
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How do we calculate its wavelengh?
Wavelengh= 2L. This is beause distance between adjacent nodes = 1/2 wavelengh.
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What is its frequency therefore?
f0 = v/wavelengh o = v/2L.
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First overtone? Its node arrangement?
String in two loops, node in the middle and at ends.
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What is its wavelengh and what is its frequency?
Wavelengh = L because two loops. f1= v/wavelengh.
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How can we use this to calcuate the fundermental?
v/L = 2f0.
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Second overtone?
3 loops. Each node is 1/3 L from either end, antinode in the middle.
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Wavenlgh & frequency?
Wavelengh = 2/3 L. F= v/Wavelengh
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What is the pattern with the fundermental about the frequencies?
Multiply the f0 by a number eg: second overtone is 3f0 for the f2.
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Card 2

Electromagnetic?

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vibrating electric and magnetic fields that progress through space without need for substance.

Card 3

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What is a transverse wave? Whats the opposite? Definition?

Card 4

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What is polarisation?

Card 5

Front

What is an unpolarised wave?