Light as a wave + Waves&WaveMotion Flashcards
(111 cards)
1
Q
Spectrometer
A
Used to study light (as a wave)
2
Q
What spectrometer consists of
A
Collimator (c)
Telescope (t)
Circular scale
Rotating table
3
Q
Collimator
A
Tube with a slit (s) at one end and a converging lens at other
4
Q
Telescope
A
With corsswires in the eyepiece
5
Q
Circular scale
A
Marked in degrees with vernier scales attached
6
Q
Rotating table
A
With three levelling screws
7
Q
Spectrometer set up
A
- Adjust eyepiece until crosswires can be seen clearly
- Focus the telescope on a distant object
- Place a lamp in front of the slit, place telescope in line with collimator
- Adjust slit to give narrow beam of light
- Adjust telescope until image of slit coincides with crosswires without parallax
- Level the table
8
Q
Camera
A
- Mimics how eye works
- Lens can be moved in/out
- Amount of light entering camera
9
Q
Prism
A
- Using a prism, Isaac Newton found that white light can be split up into its spectrum of colours through a process called dispersion
- It is split up into seven colours: roygbiv
10
Q
Dispersion
A
the splitting up of white lgiht into its constituent colours
/ separation of light into its diff colours/frequencies/wavelengths
11
Q
Dispersion - why it happens
A
They split up like this because different colours have different wavelengths, as light travels through different media long wavelengths are refreacted least, short wavelengths are refracted more
12
Q
Primary colours
A
Red, green, blue
13
Q
Secondary colours
A
Combinations of primary colours
14
Q
Complementary colours
A
A primary colour + a secondary colour which together give white (eg. blue and yellow)
15
Q
Dispersion by a grating
A
- Light is diffracted + dispersed when it goes through a grating
- Red light is deviated the most (longest wavelength), violet the least (shortest wavelength)
- No overlap of the spectrum occurs when using a grating
16
Q
The diffraction grating
A
Square of plastic with slits in it
17
Q
Distance formula for diffraction grating
A
d = 1/600 mm
d= 1/600 / 1000 m (metres)
the 600 is how many lines per mm, eg. can be 400 or 500, etc
18
Q
Diffraction grating equation
A
nλ = d sinΘ
n = number of images λ = wavelength (lambda) d = diffraction of grating constant Θ = angle (theta)
19
Q
max number of images to one side of grating
equation (highest order image formula)
A
nₘₐₓ = d/λ
20
Q
Infra-red applications
A
- Used to heal damaged muscle
- To take thermographs of the body
- Remote controls for TV + Radio
- Burgular alarms
- Fire-fighters use IR viewers to find unconscious people
21
Q
Ultraviolet
A
Given off by the sun, helps to produce Vit. D can cause sunburn + cancer
Ozones layer absorbs most of UV radiation
22
Q
Ultraviolet application
A
- UV lightbulbs
- Washing powders
- Security pens
23
Q
Microwaves
A
Radio waves of short wavelenghts
24
Q
Microwaves application
A
- Communication - travel in straight lines from transmitter to receiver within 40 miles of each other
- Cooking - microwaes are reflected by metal but absorbed by water, sugar and fat
25
Fraunhofer lines
Emission spectrum
| Absorption spectrum
26
Emission Spectrum
A spectrum given out by a substance when its atoms are excited
27
Absorption Spectrum
.A spectrum that is continuous except for certain missing wavelengths (absorbed by gases) (first measured by German Joseph von Fraunhofer)
28
Types of colours
primary colours
secondary colours
complementary colours
29
Grating constant
The distance (d) between two adjacent slits on thegrating is called the Grating Constant
30
Lines in diffraction grating
has 400/500/600 lines per mm usually
31
Infra-red
Given off by warm objects
32
What does LASER stand for
Light Amplification by Stimulated Emission of Radiation
33
What does a laser tube do
A laser tube produces a beam of light in which all the waves are of the same frequency and in phase
34
Application of lasers
1. Used to treat detached retina
2. Used in surgery
3. Used to cut clothing + metal
4. Used to read CDs
5. Used to scan things in shops
35
Polarisation
- Light from incandescent source is unpolarised
- If light from source is passed thru substance called Polaroid, becomes plane polarised. (light is vibrating in one place only)
- If second Polaroid is rotated thru 90 degrees, virtually no light gets thru. Since only transverse waves can be polarised, the fact that light can be polarised shows light is a transverse wave.
36
Stress polarisation
This phenomenon is called photoelasticity + it's used by engineers to analyse stresses in components
37
Light that passes through the diffraction grating makes an angle theta with the normal to the grating
1. Parallel rays of monochromatic light of wavelength λ are incident on diffraction grating in which slit separation is d. If grating has N lines per metre, grating spacing is given by: d = 1/N metres
2. Constructive interference only occurs along a few precise directions, like when PQ = λ and when other whole number wavelengths exist PQ = nλ where n = 0,1,2,3...
3. Now: PQ = dsinθ where θ is angle of diffraction
Therefore nλ = dsinθ
38
Plural of medium
Media
39
Three possible states of substances
Substances can exist in three possible states:
Solid
Liquid
Gas
40
Waves and medium
When a wave passes through a solid/liquid/gas. we say it passes through a medium.
If it doesn't, it does not need a medium.
41
Categories of waves
Mechanical
| Electromagnetic
42
Mechanical
Waves that need a medium are called mechanical.
They travel through vibrations of molecules.
eg. water wave, waves on rope/spring, sound waves, ultrasonic waves
43
Electromagnetic
Waves that do not need a medium are called electromagnetic.
They travel at the speed of light
eg. radio waves, microwaves, infra-red waves, light waves, x-rays
44
Travelling wave
A travelling waves carries energy from the source to another place.
Can be either mechanical or electromagnetic
45
Periodic travelling wave
If the wave travels in a controlled pattern, it is called a periodic travelling wave, because the thing is controlled
46
Travelling waves - slinky
- When we look at a Slinky, energy can pass along its length.
- If some coils are pulled together we call this compression
- When compression is let go it travels along length
- Region left behind stretches more than normal and this is called rarefaction
47
Waves - groups
Waves can be further divided into groups depending on how they vibrate:
Transverse
Longitudinal
48
Transverse
- Waves that vibrate up + down
- vibrations perpendicular to direction of propagation of wave
- Only transverse waves can be polarised
49
Longitudinal
- Waves that vibrate lengthways
| - vibrations parallel to direction of propagation of wave
50
Eg of transverse waves
waves on a rope/string (not compression), water waves, all electromagnetic waves
51
Eg of longitudinal waves
compressions on a spring, sound waves in a medium, ultrasonic waves
52
Frequency
Frequency of a wave means how often one fullw ave, or cycle, passes a point
53
Frequency unit + symbol
Unit: the Hertz (Hz)
1 hertz = 1 cycle per second
Symbol: f
54
Amplitude
- When particles are at rest, the position they are in is the starting or resting position
- When they are vibrating due to energy being introduced they reach their amplitude, or height
The amplitude of a wave is its height
55
Starting/resting position
When the particles are at rest, the position they are in is the starting or resting position
56
Wavelength
The length of a wave, or wavelength, in the distance from one point on one wave to the same point on the next wave
-distance between two crests/troughs
57
Wavelength unit + symbol
Unit of wavelength: metre
Symbol: λ (lambda)
58
Velocity
The distance travelled by one cycle in one second is the velocity of the wave
59
Velocity unit + symbol
Unit: metre per second
Symbol: c
60
Finding c
We can work out the velocity of a wave by multiplying the frequency and the wavelength
c = fλ
61
C unit
metre per second
62
Phenomenon
An observable occurence
63
Wave phenomena
```
Reflection
Echo
Refraction
Diffraction
Interference
```
64
Reflection
The bouncing of waves off an obstacle in their path
eg. water waves, light waves, waves on a slinky
65
Echo
A sound wave reflected off something
66
Wave speed
- When waves move from one medium to another, frequency stays the same
- Wavelength increases if waves speed up
- Wavelength decreases if waves slow down
67
Refraction
When wave enters new medium + changes velocity, its direction changes (called refraction)
eg. water waves in a ripple tank
68
Diffraction
The spreading of waves into a region beyond an obstacle or gap
eg. water waves in a ripple tank, sound waves, electromagnetic waves, light waves
69
Interference
- When two waves meet, they form a new wave
- This new ave has an amplitude that depends on the values of the amplitudes of the two original waves
- Interference can be constructive or destructive
-when waves from different sources overlap, a new wave is formed
70
Interference types
Constructive
| Destructive
71
Constructive
Constructive interference happens when the resulting amplitude is greater than the amplitudes of the individual waves
72
Destructive
Destructive interference happens when the resulting amplitude is less than the amplitude of the individual waves
73
Coherent source
When two waves are in phase with each other, or there is a constant phase change. They have the same frequency
74
Interference pattern
When two or more coherent waves meet, they make a wave pattern called an interference pattern
75
Polarisation
Means controlling the vibrations of a wave so it vibrates in one plane only
Only transverse waves can be polarised
76
Vertically polarised
Polarisation is also called vertically polarised
77
Plane of polarisation
The plane through which it travels
78
finding wavelength
when using formula in exam, make sure to find average wavelength of all angles
79
finding N max
find using formula, which gives max no. of images to one side. Twice this number and add 1 to find N max.
ie. (Max images to one side + Max images to other side + central image)
80
photocell
know how to draw diagram
81
describe how a photocell conducts current
- light of suitable freq falls on cathode
| - electrons are emitted
82
a current of 2 microA is flowing in a photocell. How many electrons are generated in the photocell during each minut?
use Q = It
then use it with electron charge to find no. of electrons
83
diffraction effects of sound waves are noticeable in everyday life, whereas the diffraction effects of light are not. Explain why
- sound has a long wavelength. Noticeable in everyday life etc. sound diffracted as it goes through a window
- Light has a short wavelength. Need a diffraction grating/very small gap
84
light dispersed with a prism order of colours starting with colour refracted the least
red orange yellow green blue indigo violet
85
in Young's experiment to demonstrate the wave nature of light he needed two coherent sources of light. How might he have produced these sources?
double slits
86
calculate the energy of a photon of green light
c = fλ
E = hf
87
Quantum mechanics is used to explain how electrons in atoms produce line emission spectra. Describe how these spectra are produced.
- electrons gain energy energy to move to a higher energy level
- return (to lower energy level) emitting photon/light/em radiation
88
two differences between photons and electrons
- photons have no mass
- photons have no charge
- photons are light/electromagnetic radiation
- photons are packets/bundles of energy
89
properties of radio waves
- travel at speed of light
- electromagnetic radiation
- travel thru vacuum
90
SAR value (specific absorption rate)
SAR = W/kg
91
what happens to radio freq energy absorbed by body
converted to heat
| + carried away by body
92
why are radio freq waves not very penetrating
low freq / long wavelength / low energy
93
what are the audible freq limits for sound waves?
Lower value ≈ 20 Hz
| Upper value ≈ 20,000 Hz
94
safety precautions to take when using a mobile phone
keep phone at distance
use loudspeaker function
brief calls only
direct antenna away from your head
95
an electromagnetic wave which may induce cancer + how
x-rays
UV rays
cause ionisation of body cells
96
properties common to all types of electromagnetic waves
- same speed
- can be polarised/reflected/diffracted etc
- travel through vacuum
97
energy of a photon
E = hf
c = fλ
98
diffraction grating experiment - observation if laser was replaced with white light
spectra / dispersion / colours
99
Observation when a narrow beam of light undergoes dispersion as it passes through a prism
- red light deviated least
| - only one spectrum observed
100
Observation when a narrow beam of light undergoes dispersion as it passes through a diffraction grating
- red light deviated most
| - many spectra observed with a grating
101
example of light undergoing dispersion besides prism + grating
rainbow
102
what causes a vapour lamp to emit light
electrons changing energy levels
103
How to detect infra red
- thermometer
- temperature sensor
- photographic plate
104
How to detect ultra violet
- shine on vaseline/detergents
- effect eg. fluorescence
- glows
105
An electromagnetic radiation has a wavelength of x metres, name the section of the spectrum in which this radiation is located
- find its freq using c=fλ
| - know freqs of each section
106
Can a diffraction grating diffract x-rays? why?
no,
- line spacing must be similar to wavelength of radiation (for diffraction to occur)
- spacing between lines in a grating is too large
107
differences between longitudinal and transverse waves
- transverse can be polarise, longitudinal cannot
| - state way they travel
108
why is a fluorescent tube an efficient source of light?
-most of the electrical energy is converted to light energy
109
why does diffraction not occur when light passes through a window?
width of window is too large
110
how does the diffraction grating produce a spectrum
diff colours have diff wavelengths/frequencies
constructive interference occurs / bright images formed at different Θ
111
why is a spectrum not formed at the central (zero order) image
at central image, Θ = 0
