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Physics Sep Prediction Exams Noted > Chapter 11 > Flashcards

Chapter 11 Flashcards

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1
Q

What waves do an earthquake produced

A

P waves = longtidunal

S waves = transverse (because they look like transverse from the S😭)

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2
Q

What are progressive wabes

A

A progressive wave is an oscillation that transfers energy from a source to a receiver through a medium WITHOUT TRANSFERING MATTER

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3
Q

How does this work with sound

A

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

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4
Q

How does it work in general

A

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

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5
Q

Transverse vs longtidunal

Similarities?

A

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

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6
Q

What do longtidunal waves always need and what can’t happen to a longtidunal wave

A

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

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7
Q

Transverse and lomgtifunal edamples

WATER!

A 
Transverse = S waves, electromagnetic , water waves , springs 
Longtidunal = sound , slinky, p waves,
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8
Q

Longtidunal example of sound

A

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

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9
Q

Key words

Dispalcmemr

A 
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

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10
Q

Relationship between frequency and time period

Wave speed

A

1/f = time period
1/time = frequency
= frequency times wavelentgh

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11
Q

How to get wave speed equation

A

Speed = distance / time
Distance = wavelentgh
Time = 1/frequency
= Wave,either x frequency

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12
Q

How to get from freq to time periods

A

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

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13
Q

Phase difference

A

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

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14
Q

Phase difference equation

A

Difference in displacement
/ wavelentgh * 360

Or x 2pi

Can be same wave

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15
Q

What part on a graph is it at maximum velocity and accerlwiton

A

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

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16
Q

How to use an OSCILLOSCOPE TO DETERMINE WAVE FREQUENCY

A

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

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17
Q

Why does sound mvoe faster in a denser medium than air

A

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

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18
Q

Reflection

A

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

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19
Q

Waveformts

Also hast about ohase sifferenc here

A

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

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20
Q

Cohernede early doors

A

Same frequency and in phase

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21
Q

LAW OF REFLECRION, where do the angles feature?

A

Angle is between NORMAL AND THE WAVE (even fir refraction), not wave and the boundary!

Very I prow the fir basic fundsmentale

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22
Q

What is refraction
Why does this happen anyways
What happens always when a wave Fred acts

A

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

23
Q

What are the speed differences of mediums ?

A

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

24
Q

Mcieopspes dirffraciron

A

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

25
Q

What is diffraction

What changes

A

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

26
Q

Again gal

A

If the spgaonis smaller than the wbakentgj it will diffract, smaller the better!

27
Q

What is polarisation

A

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

28
Q

How are two ways in which polarisation takes placem

A

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

29
Q

Polarisation using METAL FILTERS, what must be direction if railings?

A

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

30
Q

However scrap thst, what about Polaroid filters inngnerkan

A

If it is VERTICALLY ALLIGNED THEN IT WILL ONLY ALLOW VERTICAL / component of be.ticslmplane through

If horizontally slligjed only allow horizontal throuhbj

31
Q

Do the plane of waves have to perfectly line up? What is

Think aboutnthisninntermenif two polarising filters , yiu rotisre one

A

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

32
Q

What happens to the intensity from UNPOLARISED TO POLARISED COMOLELTY UNPOSLRISED SLL DIRECTIONSN

A

Intensity drips to 50°!!!

33
Q

How much intensity if the polarised wave is left?

A

Intensity is properinsk to cos theta sqaured, where theta is angle between components

34
Q

Again waves reflection polarisation

A

Partially polarised mostlynhrodionttls sunglasses berirfkaky aligned reduce shkare

35
Q

Question with uptkipem filters

A

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

36
Q

Again refraction causing partial refleciron

A

Refractijncausssmoartisl reflection whcihcsides partial pos,rissifommso dinglssses

37
Q

Imt situ ruled

A

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

38
Q

Laser lights

A

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

39
Q

How does aligning aerials work?

A

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.

40
Q

Okay equation for intensity of a PROGRESSIVE WAVE (so for sound, water and em:

A

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

41
Q

From a source however?

A

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

42
Q

Intensity with waves spreading out

A

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 !

43
Q

How to calcukten the refractive index

A

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

44
Q

Refraction law snellius

A

N1 sin theta = n2 sin theta

Substitut values and remember it’s with the NORMAL!!!

45
Q

What is total internal refkefiroj

2 conditions

A

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

46
Q

Thus equation fir fir Ivan

Why does n2 smaller)

A

N1 sin1 = n2 sin90

So theta = invers sin (n2/n1)

This is why n2 smaller or else the inverse function is invalid

47
Q

Rules fir critical

A

If angle incidence smaller it refracts
If the same 90°
If buffer = TIR

48
Q

So if you want more TIR (diamond cutter) what dinyounwant

What do you want from refractive index then

A

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

49
Q

Sound waves work

A

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

50
Q

How to calculate the refractive index using a curved device

A

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

51
Q

Fibre optics

A

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

52
Q

What two thingd must happen to see amfibre optic cable good for transfer of DST’s

A
  • 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
53
Q

How to describe wave cycle

A
  • 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!!!

Physics Sep Prediction Exams Noted (15 decks)

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