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A-Level Physics - OCR A > M4 Waves - Part 1 > Flashcards

M4 Waves - Part 1 Flashcards

features of waves, phase difference, EM waves, polarisation, intensity

1
Q

define wave

A

periodic disturbance in a material or space
each particle vibrates about a fixed position
energy is transferred outwards from the source of the wave

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2
Q

what are progressive waves

A

an oscillation that travels through matter, transferring energy.
when traveling through a medium, particles move from equilibrium position to a new position.
the displaced particle experiences a restoring force from neighboring particles and returns to its original position.

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3
Q

what types of waves are transverse and longitudinal

A

progressive

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4
Q

define transverse waves

A

the direction of vibration is at 90 degrees to the direction of energy transfer
these have crests and troughs

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5
Q

give examples of transverse waves

A

EM waves
waves on water
s waves in earthquakes

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6
Q

define longitudinal wave

A

the direction of vibration is parallel to the direction of energy transfer. these have compressions and rarefactions

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7
Q

give examples of longitudinal waves

A

sound waves

p waves in earthquakes

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8
Q

define mechanical wave

give examples

A

these waves require a material/medium to transfer through
produced by oscillation of particles in a medium
eg. sound or water

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9
Q

define electromagnetic waves

A

these waves require no medium and so can transfer energy through a vacuum
produced by acceleration of charged particles

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10
Q

define amplitude

A

the maximum displacement of the wave in either the positive or negative direction (from equilibrium position)
unit is m

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11
Q

define displacement of a wave

A

distance of a point from the equilibrium position in a particular direction (vector)
has positive or negative direction

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12
Q

define wavelength

A

Distance between 2 points in phase on adjacent waves

eg. distance between two successive crests

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13
Q

define frequency

A

number of oscillations/vibrations (at a point) per unit time

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14
Q

define period

A

time taken to produce one complete wave

symbol = T

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15
Q

define wave speed

A

distance travelled by a wave per unit time

symbol = v

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16
Q

define phase difference

A

difference between displacements of particles along a wave
a complete wave = 360 degrees or 2π radians
in phase = phase difference of 0
units = degrees or radians

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17
Q

derive v = fλ

A 
s = d/t
distance = wavelength
time = period
s = wavelength / period
period = 1/frequency
s = wavelength / 1 / frequency 
s = wavelength X frequency
s = v
v = f X λ
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18
Q

classify the following waves:

a) sound
b) light
c) water
d) x-rays
e) microwaves

A

a) sound = longitudinal and mechanical
b) light = transverse and electromagnetic
c) water = transverse, sometimes longitudinal and mechanical
d) x-rays = transverse and electromagnetic
e) microwaves = transverse and electromagnetic

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19
Q

what are all the basic wave properties of EM waves

A 
reflection
refraction
diffraction
polarisation
interference
energy transference
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20
Q

what is the speed of EM waves

A

3 X 10^8 ms^-1

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21
Q

which of radio waves or gamma rays has the longest wavelength?

A

radio

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22
Q

what is the wavelength of radio waves

A

10^-1 - 10^6

23
Q

what is the wavelength of microwaves

A

10^-3 - 10^-1

24
Q

what is the wavelength of infrared waves

A

7 X 10^-7 - 10^-3

25
Q

what is the wavelength of visible light waves

A

4 X 10^-7 - 7 X 10^-7

26
Q

what is the wavelength of ultraviolet waves

A

10^-8 - 4 X 10^-7

27
Q

what is the wavelength of x-rays

A

10^-13 - 10^-8

28
Q

what is the wavelength of gamma rays

A

10^-16 - 10^-10

29
Q

on a EM wave, how do the magnetic and electric field relate

A

they are perpendicular to each other

30
Q

radio waves
what can it penetrate through?
what are the uses?

A

pass through matter

radio transmissions

31
Q

microwaves
what can it penetrate through?
what are the uses?

A

mostly pass through matter but causes some heating

32
Q

infrared
what can it penetrate through?
what are the uses?

A

absorbed by matter, causing it to heat up

heat detectors, night vision cameras, remote controls and optical fibres

33
Q

visible light
what can it penetrate through?
what are the uses?

A

absorbed by matter, causing heating

human sight, optical fibres

34
Q

ultraviolet
what can it penetrate through?
what are the uses?

A

absorbed by matter, cause some ionisation

sunbeds, security marks that show up under UV

35
Q

x-rays
what can it penetrate through?
what are the uses?

A

mostly pass through matter, cause ionisation as they pass

see the damage to bones and teeth, airport security scanners, kill cancer cells

36
Q

gamma rays
what can it penetrate through?
what are the uses?

A

mostly pass through matter, cause ionisation as they pass

irradiation of food, sterilisation of medical instruments, kill cancer cells

37
Q

what waves does polarisation effect

A

transverse waves

38
Q

describe an experiment to demonstrate the polarisation of microwaves

A

Place microwave transmitter and receiver facing each other
Rotate one of them through 90 degrees about axis
Observe signal fall to zero from initial high value on meter monitoring output of the receiver
Use 2 polarising filters and rotate from parallel to crossed

39
Q

how is polarisation used in microwave ovens

A

unpolarised rays of microwaves are prevented from leaving the microwave by a fine metal grid covering the door
this grid absorbs both horizontal and vertical oscillations of the microwaves

40
Q

draw a diagram which represent unpolarised light

A

a line with dots with arrows going up and down

41
Q

draw a diagram to show vibrations of E-field in unpolarised light

A

a dot with arrows going out in lots of directions

42
Q

draw a diagram of how a polaroid is used when the first one to the light is verticle and the next one is horizontal

A

unpolarised light goes in the vertical polaroid and keeps going through but is stopped by the horizontal polaroid

the vertical polaroid is called the polariser
the horizontal polaroid is called the analyser

43
Q

draw a diagram to show polarised light by relfection

A

look it up

pg 10 of 1st waves booklet

44
Q

what is plane polarised light

A

when all of the waves are in the same plane

applies to transverse waves

45
Q

why is light from a candle unpolarised

A

every wave is aligned in a random and different plane

46
Q

what is reflection

what is the law of reflection

A

all waves reflect off a surface
for a plane surface , the angle of reflection = angle of incidence
normal is drawn perpendicular to the surface

47
Q

what is refraction

A

if waves goes through a boundary, their speed and wavelength changes
if they are incident at a non-zero angle to the boundary then they will change direction

48
Q

what is diffraction

when does max diffraction happen

A

waves that pass through a gap or around an obstacle will spread out
maximum diffraction happens when the gap is similar in size to the wavelength of the wave

49
Q

what is the intensity of a progressive wave

A

the power passing through a surface per unit area

unit is Wm^-2

50
Q

how does intensity and distance relate

A

intensity decreases with distance
I is directly proportional to 1/r^2
when they give a distance in a question it means the radius

51
Q

how does intensity and amplitude relate

A

decreasing amplitude means reduce in average oscillating speed of particles
I is directly proportional to A^2
eg. doubling the amplitude means 4X the intensity

52
Q

what are the proportionalities you need to know for intensity

A

I directly proportional 1/r^2

I directly proportional A^2

53
Q

if the distance from earth to the sun is 1.5 X 10^11 m and the intensity is 1400 Wm^-2 then what is the power

A 
I = P / A
P = AI
A = 4πr^2
= (4π(1.5 X 10^11)^2) X 1400
= 4X10^26 W

A-Level Physics - OCR A (20 decks)

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