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Physics year 12 > Chapter 11 - Waves 1 > Flashcards

Chapter 11 - Waves 1 Flashcards

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1
Q

what is a progressive wave

A

“a progressive wave is a transfer of energy but not matter from one place to another through an oscillation”

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2
Q

what is the key feature of a longitudinal wave
oscillations
squishes etc.

A

oscillation occur parallel to the direction of travel
has compressions and rarefaction’s
a full wavelength is the distance between two compressions etc.

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3
Q

what are the key features of a transverse wave

A

oscillations occur perpendicular to the direction of travel

there are peaks and troughs where one full wavelength is the distance between two troughs or two peaks

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4
Q

how do particles move from their equilibrium positions in the two types of wave

A

in a transverse wave the amplitude shows the greatest distance from their equilibrium positions that they move
in a longitudinal wave the particles vibrate about their equilibrium positions but do not move

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5
Q

what is the wave equation

A

v = f x (lambda)

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6
Q

relationship between period and frequency

A 
f = 1/t
T = 1/f
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7
Q

define displacement, symbol and unit

A

s, m

distance from the equilibrium position in a particular direction (vector)

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8
Q

define amplitude, symbol and unit

A

A,m

maximum displacement from equilibrium position

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9
Q

define wavelength, symbol and unit

A

(lambda), m

minimum distance between two points in phase on adjacent waves

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10
Q

define period, symbol and unit

A

T,s

the time taken for one complete oscillation or wavelength

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11
Q

define frequency, symbol and unit

A

f, Hz

the number of wavelengths passing a set point per unit time

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12
Q

define wavespeed, symbol and unit

A

v (or c), ms^-1

the distance traveled by the wave per unit time

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13
Q

what happens in reflection

A
  • occurs when a wave changes direction at a boundary
  • angle of incidence = angle of reflection
  • frequency and wavelength do not change
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14
Q

what happens in refraction

A
  • occurs when a wave changes direction as it speeds up or slows down when it moves from one medium to another (based on refractive index)
  • slows down = moves towards normal
  • speeds up = moves away from normal
  • refraction affects wavelength but not frequency because wavespeed changes
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15
Q

what is diffraction

A

when waves pass through a gap or travel around an obstacle they spread out

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16
Q

what changes during diffraction

A

nothing

wavelength, frequency and speed remain the same

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17
Q

what affects diffraction

A

size of gap relative to wavelength

when wavelength is equal to the size of the gap there is maximum diffraction

18
Q

what is a polarised wave

A

a polarised wave is one which only oscillates in one direction
this means it is only in one plane so is plane polarised

19
Q

what does light from an unpolarised source have

A

light from an unpolarised source has many planes of oscillation but all are at 90 degrees to the direction of travel

20
Q

can longitudinal waves be polarised

A

no they already are, they only have oscillations in one plane (the direction of movement)

21
Q

define intensity

A

“the radiant power per unit area of a progressive wave where”

I = P/A

22
Q

intensity equation

A

I = P/A

intensity (Wm^-2) = power (W) / area (m^2)

23
Q

what happens when a wave spreads out from its source (proportionality)

A

When a wave spreads out from its source, the power is spread over a larger area so intensity decreases
due to the equation for S.A. of a sphere 4pir^2

you end up with I=k/r^2
intensity is inversely proportional to the radius squared

24
Q

what happens to intensity when amplitude changes

A

when amplitude decreases the particles oscillate less giving less kinetic energy and because Ek is proportional to V^2
intensity is proportional to amplitude^2

25
Q

do EM waves need a medium

A

no

26
Q

what are EM waves

A

EM waves are transverse waves which have electric and magnetic components which oscillate and 90 degrees to both each other and the direction of travel

27
Q

can EM waves be reflected, refracted, diffracted and plane polarised

A

yes

28
Q

order of EM spectrum in decreasing wavelength/increasing frequency

A

radio waves = >10^6 –> 10^-1 m

microwaves = 10^-1 –> 10^-3 m

infrared = 10^-3 –> 7x10^-7 m (700nm)

visible light = 700nm –> 400nm

UV = 4x 10^-7 –> 10^-8 m

X rays = 10^-8 –> 10^-13

Gamma rays = 10^-10 –> anything smaller

29
Q

what are most naturally occurring waves

A

unpolarised

30
Q

what do polarising filters do

A

they vary depending on wavelength but they only let one polarisation of light pass through

31
Q

what are some uses of polarising filters

A

3D films, photography etc.

32
Q

what happens with 2 polarising filters

A

the intensity of light will change from full to nothing as they go in and out of phase

33
Q

how to calculate refractive index from speed values

A

n = C1/C2

n is refractive index, C1 is speed of light in first medium, C2 is speed of light in second medium

34
Q

what is snells law

A

n1 sinX = n2 sinY

35
Q

typical refractive index values

A 
vacuum and air = 1
water = 1.33
olive oil = 1.47
glass = 1.5
diamond = 2.42
36
Q

what are the two conditions for TIR

A
  • going from a higher refractive index to a lower refractive index
  • the angle to the normal is > critical angle
37
Q

calculating critical angle

A

n1 sinC = n2 sin(90)

38
Q

Define phase difference

A

The difference in displacement of particles on a wave or on different waves

39
Q

what features of EM waves remain constant throughout the spectrum

A
  • all travel at the speed of light in a vacuum
  • all are transverse
  • all can be plane polarised
40
Q

what features of EM waves change throughout the spectrum (other than frequency and wavelength)

A
  • the human eye’s sensitivity to the light
  • how they diffract for a given gap size
  • the heating effects of infra-red vs others

Physics year 12 (12 decks)

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