Chapter 12 Flashcards
What is the principle of superposition
When two waves meet at a point snd superpose, the resultant displacement at that point is equal to the vector addition of the displacements of bith wages
As a result this can be bigger , smaller or nothing compsred to what waves where like eitre
What happens when two waves continuously superose, what is this called
They suppose pose and produce a resultant wave with a dispalcemtnequalmtonthe sum of vector displacement, known as an INTERFERENCE PATTERN
Where they meet in phase, then maximum posit be displacements and negatives one meet each other, creating a displacement with maximum amplitude, this is CONSTRUCTIVE INTERFERENCE
Where they meet in ANTIPHASE, the maximum displacement of one peak meets with the minimum displacement of wnother trough, so the vector sum of these leaves zero amplitude (or less) this is destructive interfernece
How do interference and superposition cause waves that have different intensities
As intensity proprtional to amplitude sqaured, if suporospiton causes an increase in amplitude, intensity will increase or decreases too, causing it be brighter, louder stringer sound if constructive and dimmer weaker quieter if desrcifiobe
If a plotufe 0 then quiet too
What does coherence mean
Having CONSTANT PHASE DIFFERENCE , which means must have the SAME FREQUENCY
How to produce a CONSTANT INTERFERENCE PATTERN
A constant interference pattern means the same pattern being seen.
This only happens if incoming waves are COHERENT and have the same phase difference each time, whatever it may be. This way only one pattern is seen
If they keep changing phase difference due to change of frequencies (like raindrops)
There will be an interference pattern but it’d just one that keeps on changing
So needs to be coherent = frequency same = phaendifferncethe same
What happen if wave like light in general superpose (knowing that they aren’t coherent)
Fact that filament lamps emit a range of reauenices meam that they are never cohener, and always produce unstable interference pattern
This cannot be resolved and detected, we just see this as CONSTANT LIGHT
What is miminima and maxima in interference patterns (constant ones)
Minima is ooijte if minimum amplitude, meaning points where the waves meet in antiphase and destcutirive interferenfe
Maxima is points of maximum amplitude, so points where waves meet in phase and so constructive intefrenece
What is PLD
Path length difference for a point where two cohenernt waves (remember this means constant phase difference not they are in phase) is just the difference in distances from the source of the waves to thst point
However if this difference is an INTEGER multiple of the wavelentgh of the waves, then it meets here in PHASE, so it will constructively interfere to produce a MAXIMA
And if it is a half integer multiple wavelentgh of then it meets in NAITPHADE and so will destructively interfere producing a minima amplitudem
Again for pld phsse thing what had to be of the wave
S must be cohenerent to produce stable interferenfe , otherwise no point finthry keep changing phsse
How do the orders of inter fence go
Where they meet equidistant from each other, the path lens difference is 0, so there is 0 phase difference (which is meetining in phase), thus it’d the 0 Oder CENTRAL Maxima
Then going up and own it goes in half wavelentgh PLD meaning minima maxima minima maxima
Goes like
0 1st minima 1sr maxima 2nd minima 2nd maxima
And I’m bith direcutoms
If it’s a 2nd order minima, it means 1.5 wavelentgh difference = PLD
again it meets in phase antiphase phase antiphase etv
How can you use microphone to find out the wavelentgh of a sound wave produced by speakers
What hwppejsnirnthe frequency of thr sound were halved
If the speakers are connected to the same generator then the two waves they produce will be cohenerent, as a result a stable interference pattern will be seen
Thus use microphone to find areas of minima and a,dims, measure the PLD HERE AND YOU CAN THENUSE ORDER FORUMSL TO WORK OUT THE WVAKENTGH! And dna work out frequency if you know speed of sound is 330
If the frequency of sound is halved then wavelentgh is doubled. As a result the waves suporsoption would be more spread out, and to reach the same orders, you need double the PLD now !
How to Hecke if so,etching I’d palne poslrised
Use a filter through a single place where a wave (that has been du proposed) comes out from
Rotate it @80, if it drops in intensity like expected it’d polarided, if intensity kinda constant then not polarised
To find wavelentgh First recognise where 0 order 1st order maxima etc are then measure lengths. Do sporptiste claudskruojs to find wavelentgh and average these out!
What did the young double split experiment move to show?
That light waves have properties as a WAVE rather than a particle which Newton thought it to be
What was the experiment and what did it show
Experiment was
1st to show an interference pattern you need a source of coherent waves . As a result, he used a filter against a random light source ti only give waves of one frequency, thus cohenernt
He then used a single split to diffract it, such that it could ILLUMINATE THE TWO DPLITS AFTER
the two splits after then diffract sperwtely , creating basically two source of waves that as they came from the same point source (which is coherent) are also coherent
These could then superpose and create interference patterns as they are cohener, and if they are waves
The fact that they did produce interference patterns show that light has properties like a wave, as it can create interferenfe patterns of minima and maxima dimilsr to the orders, which depend on PLD etc.
These are called fringes
It was this way using maths he was able to calculate the wavelentgh of many different spectrums of light
What does monochromatic mean
He used a filter on a source of light to produce light of a single wavelentgh (and thus frequenc7j. This was MONOCHOMSTIC LIGJT
so again to do the double split
1) need monochromatic source of light
2) slit need to be small enough tissue diffract and illuminate the other elite
Which also need to be small enough to diffract again
What is the wuation then that he found out and what condition does this only hold for
That wavelentgh =ax /d
Where a is thr slit separation
X is the fringe separation between two ADJACENT MAXIMA OF MINIMA FRINGES
And D is the distance between the slits and the fringes
Only holds true as long as the slit separation is much much bigger than the Distamce D
So that small angle approving,action can be used
And again when does this equation only hold
When D is»_space;»> then a
And that the waves cohrern t(which they are if bith fame form monochromatic cpoitm dource
If you have a laser, why don’t yiu need a filter
Laser is already monochromatic and in phase, so you don’t need filter, and since guaranteed all the light from laser is monochromatic don’t need single slit either
Need singl slit before be a use waves that escape the filter may not be I. Lande and mah reach the double slit. It’s just to make sure
Why when measuring fringe separation should you messire distance between as many as you can
Uncertainty decrease by far over a long distance, the. Just divide by how many you wanted
= much better and remember this could be a way to reduce uncertainty
