Chapter 11 Flashcards
What waves do an earthquake produced
P waves = longtidunal
S waves = transverse (because they look like transverse from the S😭)
What are progressive wabes
A progressive wave is an oscillation that transfers energy from a source to a receiver through a medium WITHOUT TRANSFERING MATTER
How does this work with sound
You hear vibrations, but the air particles don’t actually move
They vibrate and move back and make other particles vibrate , in a plane parallel to the direction of energy transfer
How does it work in general
When a progressive wave travels through a medium , the particles in medium move from equilibrium lost ion t9 a new position ,and exert forces on each other
However a displaced particle will receive a resorting force from a neighbour particle pulling it back down to postion
This is all like a chain reaction caused by the initial firing
Transverse vs longtidunal
Similarities?
Transverse wave oscillated at 90° to the direction if energy transfer, whereas longtidunal parallel in the direction of energy transfer
- transverse waves have peaks and troughs, whereas longtidunal have compressions and rarefactions
They both however are PROGRESSIVE WAVES,so they both transfer energy without transfering any matter
What do longtidunal waves always need and what can’t happen to a longtidunal wave
A longtidunal wave always needs a MEDIUM and it can’t be polarised, because polarising means confining ti a single plane, and oscillations of a longtidunal wave already move in a single plane
Transverse and lomgtifunal edamples
WATER!
Transverse = S waves, electromagnetic , water waves , springs Longtidunal = sound , slinky, p waves,
Longtidunal example of sound
Sound waves force extended causes them to be displaced, colliding with neighbours which vibrated them and also in turn provided the resulting force
As a result the vibrations can be transmitted (Endgeräte) without any particles actually moving along the wave, instead they lsciallte about their equilibrium positions and arrive back at where they started from
Key words
Dispalcmemr
Displadmer = distance from equilibrium with direction as a vector Solitude = maximum displacement of a wave from equilibrium Wavelentgh = the distance between two adjacent oscillations in phase on adjacent waves
Time period = the time it takes for ONE WAVE TO COMPLETE AN OSCILLATION
frequency is number of waves per second
Relationship between frequency and time period
Wave speed
1/f = time period
1/time = frequency
= frequency times wavelentgh
How to get wave speed equation
Speed = distance / time
Distance = wavelentgh
Time = 1/frequency
= Wave,either x frequency
How to get from freq to time periods
10 waves per second means it would take 1 wave 0.1 seconds
1 wave takes 0.2 seconds means in 1 5 waves go last
Phase difference
Related to the difference in displacements between either PARTICLES ON THE SAME WAVE, or two whole waves ckmllelth , basically a measure of sync, different in displacements of psrtifleseother on the same wave or different
If in Phase, then both points oscillating it exact same rate, they will bith reach max at same point 2 pi radians
If completely antiphase, then one reach high other reach low, pi radians
One whole wavelentgh apart is 2 pi
Calculated by finding the distance between them as a fraction of their wavelentgh, if this is even it means they are in phase etc
Phase difference equation
Difference in displacement
/ wavelentgh * 360
Or x 2pi
Can be same wave
What part on a graph is it at maximum velocity and accerlwiton
Acceleration amd as at the minimum bevause changing direction , least is at the middle
Max velocity is at the middle because the rest is either slowing down or speeding up, middle is max speed
How to use an OSCILLOSCOPE TO DETERMINE WAVE FREQUENCY
Basically oscilloscope used a microphone to convert soundwaveinto electrical signals against time
See what each square represents in time wise, and worm out when a wave ends. This way you know the time period (time taken for a wave to happen)
And thus frequency is 1/F
Why does sound mvoe faster in a denser medium than air
A denser medium means particles more closely compact to each other meaning vibrations happens quicker and speed of transfer is greater
In the air it takes longer for burbstiojsnti ferry
Particles don’t need to be as displaced to interact their neighbours do it travels fsster
Reflection
A wave changes direction when meeting a laundry between two media, still remaining at the same medium
Angles are the same
Wavelentgh and frequency do not change, the SXACT SAME
Waveformts
Also hast about ohase sifferenc here
Simply freaks of the waves, where distance between each wave font is = to the wavelentgh
As a result, when reflecting, this never changes !
Esch leak is a wavelentgh apartment= 2pi = PHASE
Cohernede early doors
Same frequency and in phase
LAW OF REFLECRION, where do the angles feature?
Angle is between NORMAL AND THE WAVE (even fir refraction), not wave and the boundary!
Very I prow the fir basic fundsmentale
What is refraction
Why does this happen anyways
What happens always when a wave Fred acts
Refraction occurs when a wave CHANGES DIRECTION upon entering s different medium of different optical density then itself
This happens because upon entering a denser medium, or less, the wave speed slows down, which means as frequency can never be changed the wavelentgh decreases or increases , causing the direction of the waves ray to been towards or away the normal
Normally when it becomes slower it bends towards the normal and away when faster
When a wave refracts, there is always also partial reflection
What are the speed differences of mediums ?
So in air more dense = slower so bend towards
But in water more deeper = faster so away, shallow is slower
Em waves become slower in dense
Mechanical waves like sound and water become faster in dense so bend away , em bend towards
Mcieopspes dirffraciron
Keep magnifying, through alerwtures spreading of light due to diffraction occurs .
This means that can’t be focussed, and can’t be avoided
Sonneed to ypuse something with wavelentgh way smaller so it don’t diffract
And that’s electrons
What is diffraction
What changes
The spreading out around a gap .
Nothing changes, frequency wavelength and speed the same
Most effective when the size of the gal is smaller than the Wavlemtgh . For example sound waves, door gal is smaller than their wavelentgh, so it diffracts and we can hear around the corner
However light wavelentgh so small it don’t diffract
Electron so small yiu need the lattice to do it
Again gal
If the spgaonis smaller than the wbakentgj it will diffract, smaller the better!
What is polarisation
The act of confining the oscillations of a wave to a single plane
Can only be done to transverse waves as longtidunal waves already confined to a single plane
Polaeisaitojnofnthese waves makes the whole wave oscialte in this plane , and if it don’t line up then a component will atleast
Only time it won’t is if it’s perpendicular , then fully hlocked out
How are two ways in which polarisation takes placem
1) through absorption ;USING POLARIOID FILTERS
2) through REFLECTION (what happens to sunglasses and glass)
In reflection, reflected waves partially polarise too, and are mostly done so to be confined in the hriosntsl plane
As a result gkssses will have filters in the vertical plane, to block out any horxionstk plane and reduce glare
Polarisation using METAL FILTERS, what must be direction if railings?
If you want to do vertical only, must be horizontal
This is bevause when horizontal, the wave will be ABSORBED, and electrons in the metal will go upside to side, creating a of but wave absirbedl
But when vertical come there isn’t enough space for the electrons to absorb to create PD, as a result it can pass
So horizontal absorbs deleoclaised moves and created or = absorbed
Vertical doesn’t have enough space to absorb snd move to create a pd so let through
However scrap thst, what about Polaroid filters inngnerkan
If it is VERTICALLY ALLIGNED THEN IT WILL ONLY ALLOW VERTICAL / component of be.ticslmplane through
If horizontally slligjed only allow horizontal throuhbj
Do the plane of waves have to perfectly line up? What is
Think aboutnthisninntermenif two polarising filters , yiu rotisre one
They don’t shave to but must be a component in thst plane
However this means some of the waves aligned with less intensity, as it’s only compientd
This reduces until you resch 90, where no comment of one plane in the other ritnendith is zero
Draw the graoh from intensity vs angle, you get 100 at 0°, to 0 at 90 and then 100 at 180 0 at 270 100mar 360
What happens to the intensity from UNPOLARISED TO POLARISED COMOLELTY UNPOSLRISED SLL DIRECTIONSN
Intensity drips to 50°!!!
How much intensity if the polarised wave is left?
Intensity is properinsk to cos theta sqaured, where theta is angle between components
Again waves reflection polarisation
Partially polarised mostlynhrodionttls sunglasses berirfkaky aligned reduce shkare
Question with uptkipem filters
Fine, component of Esch polarised wave will be able to be polarised Esch time, however Esch time the intensity dropping by cos theta squared , as logn as angle is not 90 then it can be polarised and visible
Again refraction causing partial refleciron
Refractijncausssmoartisl reflection whcihcsides partial pos,rissifommso dinglssses
Imt situ ruled
Intensity proportional to amplitude of a wave swaured
Proprtional to cos theta sqaured.
Intensity = power / area, so it is inversely prorptinal to 1 radius sqaured
I’m edamples radius is just distance from sun etc, thusn1 / distance 2
Laser lights
Is already polasied , light from filament is unpolarised, and laser light has CONSTANT INTRNSITY (diesn’t radiate over a huge area) keep that in mind
LASER LIGJT ALREADY POLARISED, AND HAS CONSTANT INTENSITY
How does aligning aerials work?
In order to reduce interference between channels, some transmit vertically poalrised planes and do,e horizontally
The reason is so that perfectly vertically allogned aerials receive less inteferencefrom horizontally and vice verca
Thus you iften see yourself aligning the aerial ti catch the alignment centre has sent out.
Okay equation for intensity of a PROGRESSIVE WAVE (so for sound, water and em:
Intensity = Power / Area
Same concept for all, over larger areas, the power is spread out much ire so at any one place the intensity is less meaning dimmer sound, brightnouss auiter less poerful
From a source however?
From a source the poeer is radiated unfirmokymin all directions, thus it is in the form of a sphere
As a result
I = P/ 4PiR2
And so I nd distance R inverselynpeorptionsk swaure
Intensity with waves spreading out
Waves spreading out also loses energy and thus loss in energy = loss in speed (1/2mv2)
Drop in speed = a drop in Amplitude
Essentially intrnsity proprtionsl to amplitude sqaured !
How to calcukten the refractive index
Just a ratio of how fast speed of light travels in the thing
So n= c/v
If it is @ then that’s air , anything abive ine idmore dense so slow down
Speed of ligjt is 3x10^8
Refraction law snellius
N1 sin theta = n2 sin theta
Substitut values and remember it’s with the NORMAL!!!
What is total internal refkefiroj
2 conditions
This is when the whole RAY IS COMPLETELY REFLECTED BACK INTO THR MEDIUM ALL THE ENRGY
Angle of incidence must be > critical angle
N1 must be greater than n2
Critical angle inthe angle of incidence required to refract across the boundary
Thus equation fir fir Ivan
Why does n2 smaller)
N1 sin1 = n2 sin90
So theta = invers sin (n2/n1)
This is why n2 smaller or else the inverse function is invalid
Rules fir critical
If angle incidence smaller it refracts
If the same 90°
If buffer = TIR
So if you want more TIR (diamond cutter) what dinyounwant
What do you want from refractive index then
You want the smallest ciritcal angle possible such that any angle IPod incidence by Liften is likely to esceed this snd TIR
As a result you want value if (n2/n@) to be as s,all as possible
So as n2 is fixed, yiu make n1 with the GREATEST REFRACTIVE INDEX POSSIBLE
In General it makes sense, refractive index bigger, refracts more lmao
Sound waves work
Particles isdikkare and collide with neighbouring osrticked, trwndfering kinetic energy in areas of compressions and rarefactions in a plane parallel to direction if energy trendfern
How to calculate the refractive index using a curved device
A curved glass will mean any where you shine ray of light, the normals are the same somit will refract at the same angle no matter what, so always straight
-mrnisnhas llowe you to get a ray in at an angle you can easily cintrom
Angle until the refracting ray is 90 at the boundary
This is your critical angle now and measure
Now use calculations to find refractive index
Resosmignnwhynagsim it is because sem circuskr block endured light enters 90 to the boundary snd does nti change direcitom , makomg it easy tk Ems dude the firifsl smoke
Fibre optics
Need to retain. Light for information sake, thus glsss inside core has huge refrsctive index comapred to the cladding, but this dumsicsllg cos he’s fir best transfer of angles for information et f
Core musthavegreater to allow TIR to even work
What two thingd must happen to see amfibre optic cable good for transfer of DST’s
- transparent to koniseabsorption of light which means loss of signal
- must have high TIR MEANS very high refractive index giving low critical angle to always reflect
- core must be narrow to prevent multimodal dispersion
How to describe wave cycle
- say hot it mixes if it’s transverse ( so perpendicukwrnrtf)
- ksciakkted ip down ti max and min posit be negative displacement
BUT WITH REFERENCE TI WAVE CYCLES MUST DO!!!
