School Science Lessons
Light, wave and particle behaviour, visible spectrum,
colour, the eye and sight
2009-10-11
Please send comments to: J.Elfick@uq.edu.au
See:
Interesting websites
Table of contents
2.1.0
Equipment, care, radiation,
lasers
4.133
Electromagnetic radiation
25.0: Waves
27.0.0 Light, wave / particle nature of
light, measure speed of light
27.1.0
Colour
27.2.0 Electromagnetic spectrum, visible
spectrum, rainbows
27.2.1 Infrared radiation (IR)
27.2.2 Ultraviolet radiation (UV)
27.3.0 Diffraction
27.4.0 Photometry, inverse square law
27.5.0 Interference, Young's
experiment
27.6.0 Polarization
27.7.0 Modern optics,
holography, physical optics, photoelectric effect
28.12.0 The
eye, structure and physiology
27.0.0 Light, wave / particle nature of light,
measure speed of light
4.68
Sundials
4.82 Phases of the moon
4.84 Solar eclipse
4.85 Lunar eclipse
4.67 Theodolite or astrolabe
4.103
Sources of light
4.104
Luminance and illuminance
4.105
Light travels in straight
lines, pinhole magnifier
2.200
Light travels in straight lines, pinhole magnifier
27.1.0
Colour
4.132.0 Colour
3.9 Mix
colours (Primary)
3.10 Make
rainbow colours (Primary)
3.11 Spin a
colour disk (Primary)
4.114
Study the spectrum with a
ray box
4.115
Emission spectrum
4.116
Incandescent lamp
4.117
Absorption spectrum
4.118
Fluorescent lamp
4.132
Colour of sunlight
4.132.0
Colour
4.133
Electromagnetic radiation
4.134
Colour experiments, diffraction
4.135
Infrared rays
4.136
Ultraviolet light
4.137
Colours in a soap film
4.138
Colours in an oil film
4.139
Colour of transparent objects, colour filters
4.140
Colour of opaque objects
4.141
Mix coloured pigments, blue
and yellow chalk
4.142
Rotate colour discs
4.142.1
Measure solar
ultraviolet radiation
4.143
Mix coloured lights
4.144
Colours of the blue sky
and the sunset
4.144.1
Colour of the sea
10.2.0
Separate with chromatography
23.8.8
Colour of the surface and the
heat absorbed
27.1.01 Three conditions for colour
27.1.02 White light
27.1.03 Colour of an object
27.1.04 Colour of a transparent object and an
opaque object
27.1.05 Additive colour
27.1.06 True colour
27.1.07 Primary colours
27.1.08 Secondary colours
27.1.09 Fast colours
27.1.1 Complementary colours
27.1.2 Subtractive colour effects
27.1.3 Projection of colours
27.1.4 Examine objects through coloured glass
27.1.5 Examine flowers through monochromatic light
27.1.6 Examine white froth
27.1.11 Recombining the spectrum
27.1.12 Complementary shadow
27.1.13 Filtered spectrum
27.1.14 Liquid cell absorption
27.1.15 Band absorption spectrum
27.1.16 Absorption spectrum of
chlorophyll
27.1.17 Metal films and dyes
27.1.18 Dichromatism
27.1.19 Colour due to absorption
27.1.50
Dispersion colour and
deviation spectrometry, deviation through a prism
27.1.51 Dispersion curve of a prism
27.1.52 Deviation with no dispersion
27.1.53 Bending dark absorption line
of Na, anomalous dispersion of fuchsin and sodium
27.1.70 Scattering, optical ceramics,
Rayleigh scattering, Mie scattering
27.1.80
Rainbows, spectrum
35.5
Colour, (Geology)
35.6
Lustre
(geology)
35.7
Transparency (geology)
35.12
Streak (geology)
27.2.0
Electromagnetic spectrum, visible spectrum, rainbows
2.209
Study the spectrum with a
ray box
4.115
Emission spectrum
4.133
Electromagnetic spectrum
27.01
Electromagnetic spectrum
27.1.11
Spectrum, Recombining
the
spectrum
27.1.16
Spectrum, Absorption
spectrum of chlorophyll
27.1.15
Spectrum, Band
absorption
spectrum
27.1.13
Spectrum, Filtered
spectrum
27.1.14
Spectrum, Liquid cell
absorption
27.1.17
Spectrum, Metal films and dyes
27.2.0
Spectrum, rainbow, Visible
spectrum, rainbow
2.209
Study
the spectrum with a ray box, dispersion
2.209.1
Emission spectrum
2.209.2
Incandescent lamp
2.209.3
Absorption spectrum
2.209.4
Fluorescent lamp
27.2.1
Infrared radiation (IR)
23.8.12
Infrared radiation
4.135
Infrared rays
27.2.2 Ultraviolet
radiation (UV)
4.142.1
Measure
solar
ultraviolet radiation
18.7.13
Chlorine lost from swimming pools in
sunlight
19.6.1
Paints, fire-retardant, anti-fouling,
fluorescent, phosphorescent (See 3.)
37.34
Avoid
solar ultraviolet radiation
37.34.1
Measure solar ultraviolet radiation
27.3.0 Diffraction
2.210
Diffraction of light
2.222
Make a spectroscope with a
diffraction grating, diffraction with a feather and a scarf
4.86
Make a ripple tank
4.87
Circular pulses
4.88
Straight pulses
4.89
Reflection at a straight
barrier
4.90
Reflection at a curved
barrier
4.91
Refraction of waves
4.92 Diffraction in a ripple tank
4.93
Sound wave patterns
4.94
Wave patterns of a tuning
fork
4.95
Seeing and feeling
vibrations that make sound waves
4.96
A bell from a spoon
4.97
Vibrating cans, string
telephone
4.98
Sound waves travel through
wood
4.99
Materials that absorb sound
4.100
Sound cannot travel through
a vacuum
4.101
The ear and hearing
4.102
The voice and speaking
27.3.1 Single slit and laser
27.3.2 White
light diffraction
27.4.0
Photometry, inverse square law
27.0.1 Brightness and efficiency of
light bulbs, photometer
27.4.1 Luminosity
27.4.1.1 Paraffin block photometer,
Joly diffusion photometer
27.4.1.2 Grease spot photometer,
Bunsen grease spot photometer
27.4.1.3 Rumford shadow photometer
27.4.1.4 Frosted globe surface
brightness
27.4.1.5 Checker board
27.4.1.6 Inverse square law
model
27.4.1.7 Foot-candle meter
27.4.1.8 Surface brightness of a
lens
27.4.1.9 Reflected surface
brightness
27.4.2 Radiation pressure, "light
pressure"
27.4.2.1 Radiometer, quartz fibre
radiometer
27.4.3 Black bodies, electric
soldering iron, Stefan-Boltzman equation
27.4.3.1 Hole in a box, Bichsel
boxes
27.4.3.2 Carbon block
27.4.3.3 Radiation from a black body
27.4.3.4 Good absorbers good
radiators
27.4.3.5 Plotting the spectrum
27.4.3.6 Variac and light bulb
27.5.0
Interference, Young's experiment
27.5.1 Interference from two sources,
ripple tank incoherence
27.5.1.1 Making double slits
27.5.1.2 Double slit and laser
27.5.1.3 Cylindrical tube
interference
27.5.1.4 Fresnel biprism, lighthouse
27.5.2.0 Gratings, interference of
polarized light
27.5.2.1 Drink-can spectroscope
27.5.2.2 Two dimensional grating
27.5.2.3 Speckle patterns in
unfiltered sun
27.5.2.4 Number of slits
27.5.2.5 Grating in air and water
27.5.2.6 Babinet's principle
27.5.2.7 Random multiple gratings
27.5.2.8 Speckle spots and random
diffraction
27.5.2.9 Speckle patterns in arc
light
27.5.3 Thin films
27.5.3.1 Soap film interference
27.5.3.2 Newton's rings
27.5.3.3 Stable black soap films
27.5.3.4 Constant soap film
27.5.3.5 Boys rainbow cup
27.5.3.6 Air wedge
27.5.3.7 Mica interference
27.5.3.8 Turpentine film
27.5.3.9 Absorption phase shift
27.5.3.10 Tempering colours
27.5.3.11 Oil film
27.5.4 Interferometers
27.5.4.1 Michelson interferometer
27.6.0
Polarization
27.6.1 Dichroic Polarization
27.6.1.1 Polaroids on the overhead
27.6.1.2 Polarization mechanical
model
27.6.1.3 Polaroids cut at 45 degrees
27.6.2 Polarization by reflection
27.6.2.1 Making black glass
27.6.2.2 Brewster's angle
27.6.2.3 Tilt the windowpane
27.6.2.4 Stack of plates
27.6.3 Circular polarization
27.6.3.1 Laser and quinine sulfate,
tonic water
27.6.3.2 Rotation by sugar solution
27.6.3.3 Three polaroids
27.6.3.4 Rotation by polarizing
filter
27.6.3.5 Barber pole
27.6.3.6 Barbershop sugar tube
27.6.3.7 Faraday rotation
27.6.4 Birefringence
27.6.4.1 Calcite crystals
27.6.4.2 Plexiglass birefringence
27.6.4.3 Pendulum model
27.6.4.4 Model of double refraction
27.6.4.5 Wavefront models
27.6.4.6 Nichol prism
27.6.4.7 Crystal structure of ice
27.6.4.8 Colour with mica
27.6.4.9 Birefringent clear plastics
27.6.5 Polarization by scattering
27.6.5.1 Sunset with a polarizer
27.6.5.2 Tyndall experiment
27.6.5.3 Polarization by scattering
27.6.5.4 Haidinger's brush
28.12.0 The
eye, structure and physiology
28.12.1 Model of the eye
28.12.2 Water flask model of the eye
28.12.3 Blind spot
28.12.4 Inversion of image on retina
28.12.5 Astigmatism
28.12.6 Eyeglasses
28.12.7 Chromatic aberration of the
eye
28.12.8 Resolving power of the eye
28.12.9 Retinal fatigue colour
28.12.10 Fluorescence of retina
28.12.11 Jarring the eye
28.12.12 Subjectivity of colours
28.12.13 Mach disc
28.12.14 Most sensitive to green
light
28.12.15 Impossible triangles
28.12.16 Square that isn't there
28.12.17 Optical illusions
28.12.18 Colour blindness
27.01 Electromagnetic spectrum
See 19.3.5: Microwave cooking |
See diagram 4.133: Electromagnetic spectrum
Type of
radiation |
Gamma rays |
X-rays |
Ultraviolet rays |
Light rays
|
Infrared rays |
Microwaves |
TV waves |
Radio waves |
| Approx. wavelength |
0.01 X 10-9 m |
10-9 m |
0.1 X 10-6 m |
0.4 to 0.7 X 10-6 m |
0.01 mm |
1 cm |
1 m |
1 km |
Light is electromagnetic radiation in all ranges, having a wavelength
from 10-7 to 10-15 metres, including radio
waves, infrared radiation, visible light, ultraviolet radiation,
x-rays, and gamma radiation. In a narrow sense, light is only
electromagnetic radiation in the visible range, having a wavelength
from 400 manometers in the extreme violet to about 770 manometers in
the extreme red. Light is considered to show both particle and wave
properties. The fundamental particle or quantum of light is called the
photon. The velocity of light in a vacuum is c = 2.997 924 58 x 108
m
/ s,
or expressed in three significant figures, c = 3.00 X 108
m / sec. In transparent materials the speed of light is less than it is
in a vacuum, e.g. 225 000 km / s in water, 200 000 km / s in glass,
29 9711
km / s in air. A medium in which the light velocity is low is called an
optically dense medium. Light can be produced by a physical change,
e.g. heating of an object or a chemical change, e.g. burning of
magnesium.
27.1.01 Three conditions for colour
1.1 The colour must be in the source
1.2
The object must reflect or transmit the colour.
1.3 The detector must
be sensitive to the colour
27.1.02 White light
It consists of all the colours of the spectrum. Colour is
quality or wavelength of light emitted or reflected from an object.
Visible white light consists of electromagnetic radiation of various
wavelengths, and if a beam is refracted through a prism, it can spread
into a spectrum, in which the various colours correspond to different
wavelengths. White light is compounded of all the wavelengths in
the proportion in
which they would occur in sunlight. The colours are red, orange,
yellow, green, blue, indigo, and violet.
So white light could be defined as the light emitted from a
perfect radiator at a temperature of 6 000 degrees absolute, the
temperature of the radiating surface of the sun. However, sunlight
already
lacks in many wavelengths before it leaves the sun's atmosphere. Also
absorption of wavelengths in the earth's atmosphere is much greater for
short wavelengths, violet to blue colours, than for
longer wavelengths, green to yellow and orange colours, than for long
wavelengths, red colour. Sunlight may be rich in long
wavelengths, red, due to the
diffraction or scattering effects of dust particles in the atmosphere
when the sun is near the horizon. The uninterrupted light from a very
hot radiator, wavelength 10 000 A or less, may be
called white light.
27.1.03 Colour of an
object
The colour
that appears when white light illuminates an object is called the
colour of the object. It depends on the selected absorbing and selected
reflection of light by the object. When you illuminate a surface, some
parts of the white light are
absorbed, depending on the molecular structure of the material and the
dyes applied to it. A surface that looks red absorbs light from the
blue end of the spectrum, but reflects light from the red, long wave
end. Colours vary in brightness, hue, and saturation, the extent to
which they are mixed with white. As the red, green and blue light mix
according to a ratio of their brightness you can obtain various
colours of light. They are called the three basic colours of light. The
mixture of equal amounts of three
basic colours makes no colour light, white light.
27.1.04 Colour of a
transparent object and an opaque object
The colour of a transparent object is a mixture of those wavelengths
which it transmits. The colour of
an opaque object has a colour due to the mixture of wavelengths it
reflects, the others being absorbed. The diffused light is the
colour of light
that the object absorbs less. The nature of the surface of an object
can affect the direct reflection of different coloured light. If the
ratio of reflection to certain colour light is greater than that of
other colour light, the object may appear the colour of this colour
light. A white opaque body, or a “colourless” transparent body reflects
or transmits all wavelengths in the same proportion as they occur in
white light. A polished silver surface may reflect 93% of the white
light incident upon it and white paper may reflect 80%, depending on
the nature of the surface and the angle of incidence.
27.1.05 Additive colour
In an additive colour effect all the wavelengths present in both, or
all, the colours are present in the resulting colour. Additive colour
effects can be produced physically by mixing coloured lights or
psychologically using a rotating disc with colours on it in sectors.
Owing to the persistence of vision the eye sees all the colours on the
colour disc combined. So the combination of blue and red lights, or
blue and red sectors on the colour disc, gives purple.
27.1.06 True colour
An object only shows its true colour when the incident light contains,
all the wavelengths capable of being reflected by the body, and
contains them in the same proportion as they occur in white light.
Otherwise the colour seen depends on the wavelengths in the light that
are reflected by the body, a sort of subtractive effect. For
example, in yellow light a true blue body appears black but if the blue
body it reflects some blue, green, and yellow, it will appear yellow.
If the light contains a larger proportion of one colour than does white
light, then the body reflects larger proportion of this colour than it
would in white light. An impure green body viewed in a yellow light
will have the yellow in it increased.
27.1.07 Primary colours
The colours red, yellow and blue (or violet) are called primary colours
because they cannot be made by mixing other colours.
27.1.08 Secondary
colours
These colours can be made by mixing two or more primary colours, e.g.
orange, green, purple.
27.1.09 Fast colours
It refers to the colours of dyes which do not readily
wash out in clothes washing water due to their chemistry.
27.1.1 Complementary
colours
These colours can be combined to give the visual effect of white light.
For example, red light, 6562 Angstrom wavelength, and green blue,
4921 Angstrom wavelength, are complementary so the resulting
additive effect is white light. Additive effects occur when the
progressive waves comprising the different colours are added. Project
these two colours from separate sources onto a white screen. The
reflected light is an additive effect and so appears white.
27.1.2 Subtractive colour
In a subtractive colour effect only those wavelengths common to both
colours are present in the resulting colour. Subtractive colour effects
are obtained by mixing pigments or superposing sheets of coloured
transparent material. If you mix blue and yellow pigments, the blue and
yellow are probably not pure. The blue absorbs practically all the red,
orange and yellow and reflects a large proportion of green, and most of
the blue, so it appears blue. The yellow pigment absorbs the violet and
blue and reflects most of the green, yellow and orange and some red.
The only colour reflected by both pigments is the green, and so the
colour of the mixed pigments is green. All the other colours are
absorbed by one of the pigments.
These effects are produced when different substances subtract groups of
wavelengths from the original light, as in the mixing of pigments.
1. Mix red and yellow pigments. The mixture appears orange, a mutual
colour.
2. The subtractive effect for pure blue and pure red is black. Mixing
pigments of blue and red gives black when the colours are saturated,
i.e. no white light mixed with colour. In practice, the resulting
colour is generally purple.
27.1.3 Projection of
colours
1. Use four lanterns to project on a white screen slides coloured red,
yellow, green, and blue. The reflected light is an additive effect and
so the screen appears white.
2. Mount the four slides coloured red, yellow, green, and blue on
the one projector so that light from the projector passes successively
through the four slides. The red slide transmits the wavelengths which
constitute red, but absorbs the other wavelengths. Similarly the other
slides do the same.
The light transmitted by one slide will be absorbed by another slide.
There is no reflected light due to the subtractive effect so the screen
appears dark.
27.1.4 Examine objects
through coloured glass
Examine a red, white and blue flag through red glass and then a blue
glass. When examined through red glass, the red regions appear deep
red, the white regions appear red, and the blue regions appear black.
When examined through blue glass, the blue regions appear deep blue,
the white regions appear blue, and the red regions appear black.
27.1.5 Examine flowers
through monochromatic light
Examine a bowl of flowers of various colours is illuminated by
monochromatic yellow light. The flowers appear various shades of yellow
to black, depending on the amount of yellow light reflected.
27.1.6 Examine white
froth
Examine the white froth on a dark drink, e.g. beer. When light passes
through a transparent coloured body the amount of absorption and so the
depth of colour seen depends on the thickness of the body. The film of
liquid surrounding the bubbles of air in the froth is very thin
and so the absorption of light passing through it is negligible. The
white froth is seen by light reflected from the bubbles.
27.1.11 Recombining the spectrum
Recombine the spectrum after passing through a prism to get white light
or remove a colour and get the complement. Obtain a spectrum with a
prism, reflect out a colour with a small thin mirror and recombine the
light with a lens.
27.1.12 Complementary shadow
Shadows of red and white lights illuminating the same object from
different angles appear to produce green light.
27.1.13 Filtered spectrum
Part of a beam of white light is projected through a prism When a
filter is inserted in the beam the spectrum and transmitted light are
compared.
27.1.14 Liquid cell absorption
An absorbing solution is placed in a liquid cell placed in a beam
of light before dispersion.
27.1.15 Band absorption spectrum
A flask of nitrous oxide is placed in the beam of white light before
dispersion by a prism spectroscope. Didymium glass and dilute blood are
also suggested.
27.1.16 Absorption spectrum of chlorophyll
Examine the absorption spectrum of chlorophyll obtained by macerating
leaves in methyl alcohol.
27.1.17 Metal films and dyes
A thin film of gold transmits green but looks red yellow by reflection.
Dyes also transmit and reflect different colours.
27.1.18 Dichromatism
Green cellophane transmits more red light than green. Stack lots of
sheets and the colour of transmitted light changes from green to red.
27.1.19 Colour due to absorption
Light from a projection lantern reflected off red, green and blue
glass
to the ceiling is the same but the transmitted light is coloured by
absorption.
27.1.50. Dispersion colour and deviation
spectrometry, deviation through a prism
White light consists of all the colours of the spectrum. Dispersion is
the splitting of white light into the colours of the spectrum (violet,
indigo, blue, green, yellow, orange, red). Refractive index violet
light
> refractive index red light so violet light refracts more than red
light. Single colour monochromatic light does not disperse.
27.1.51 Dispersion curve of a prism
Light passes through a grating and then through a second slit at right
angles and a prism generating a dispersion curve in colour on the
screen.
27.1.52 Deviation with no dispersion
Light passed through oppositely pointed crown and flint glass prisms
adjusted to give light deviated in two directions but with no
dispersion. Light passes through prisms of crown and flint glass
adjusted to give two beams of the same dispersion but different
deviation.
27.1.53 Bending dark absorption line of Na,
anomalous dispersion of fuchsin and sodium
When salt is heated on a flame in the path of a narrow beam of light
before dispersion the edges of the spectrum close to the dark band bend
up or down.
27.1.70 Scattering, optical ceramics,
Rayleigh scattering, Mie scattering
1. Red and blue beam
A red beam is passed through a solution of gum mastic but a blue beam
is not.
2. Colour of smoke
Cigarette smoke is blue but after exhaling is white.
3. Multiple scattering in darkening of wet
sand and whiteness of milk.
4. Dust halos
A glass plate covered with dust is held in a beam that converges into a
hole in a screen. Circular halos appear on the screen around the hole.
27.1.80 Rainbows , spectrum
See diagram 27.1.80: Spectrum on the
wall
1. Use a shallow dish of water to form a spectrum on the wall or on a
screen. The light from the sun has to first pass through the water then
be reflected back on the wall by the mirror. This experiment needs very
fine adjustment to the angle of the mirror. Also the spectrum forms
only when the water is still so careful adjustment and patience is
needed!
2. Make a spectrum with a fine spray garden hose. Most children will
have seen the rainbow produced from the fine spray of the garden hose
in the sunlight.
3. Time of appearance of a rainbow
The rainbow consists of nearly circular arcs of colour with a
common centre. When you see a rainbow the sun is behind you and
the common centre is in the direction to the sun. Rain is falling in
the direction of the rainbow. When you see a rainbow, note the
time and angle of elevation of the sun. The rainbow is part of a
circle with its centre below the horizon. When the sun is higher than 42o
the rainbow is completely below the horizon. So a rainbow can be seen
in the morning or afternoon but not at midday.
Rainbows are usually seen about individual cumulus or cumulonimbus
clouds that have gaps between them to allow sunlight to fall onto
raindrops. The sunlight enters the raindrops and and reflect off the
the inside of the far surfaces to return towards the sun. Different
wavelengths reflect at different angles to split the spectrum. The
light from a rainbow comes towards the observer in the same way that
sunlight reflections on the sea surface come towards the observer. The
sky within the rainbow appears brighter than outside it. A secondary
dimmer rainbow with reverse order of colours may appear within the
primary rainbow. A dark region between the primary and secondary
rainbows is called Alexander's dark band. Rainbows are seen in fogs,
fogbows, when sunlight from behind the observer passes through a break
in the fog. Also a rainbow may be seen from an aircraft window when
looking down on the shadow of the aircraft on cloud below. A corona may
be observed around the moon consisting of a central white disc wider
than the moon with a faint spectrum ring of colour around it.
4. Artificial rainbow
Form a vertical circle rainbow by placing a tube of water between a
prism and screen. Use a single sphere with the back surface coated with
a reflecting material to show both primary and secondary bows with
increased intensity.
5. Rainbow droplets
Small droplets formed by spraying an atomizer on a soot covered glass
plate glisten like coloured jewels when viewed at degrees. Use small
glass spheres to generate bows and halos.
6. Arc lamp
An arc lamp directed at a sphere of water forms a rainbow on a screen
rainbow
27.3.1 Single slit and laser
1. Shine a laser beam through single slits of various sizes.
2. Adjustable single slit
Look through a vernier calliper towards a monochromatic light 5 to 10 m
distance. Look at a filament through a dark plate with a line scratched
in it.
3. Single and double slits
Rule single and double lines on a photographic plate. Look at a line
filament covered with half red and half blue filters.
4. Single and double slit projected
Focus a slit on the wall and place photographic plates with slits near
the lens. For the single slit parallel lines are unevenly spaced. For
the parallel slit pairs of lines of equal spacing are randomly spaced.
27.3.2 White light diffraction
1. A slit is projected on the wall and a second slit is placed at the
focal point of the lens.
2. Electric razor detector sweep
A mirror mounted on an electric razor is used to sweep a diffraction
pattern across a sensitive photodiode and the resulting pattern is
displayed on an oscilloscope.
3. Diffraction about a circular object
A coin is placed between a pinhole and a screen. A small hole is
punched in the screen in the shadow of the coin. While looking at the
coin through the hole ring of light will be seen. Project the shadow
from a point source onto a translucent screen.
4. Diffraction around knife edge
Slowly move a knife edge into a laser beam.
5. Diffraction pattern of a hair
Put a hair in a laser beam.
6. Shadow of a needle
A point source is placed behind a pair of needles.
7. Pass the razor blade
Hold a razor blade close to the eye so as to cut off part of an arc
lamp.
8. Arago's (Poisson's) spot
Shine a laser beam at a small ball and look at the diffraction pattern.
A laser beam is diffracted around balls.
27.4.0 Photometry, brightness and efficiency of
light bulbs, photometer, luminance and illuminance, incandescent
lamp, photoelectric cell, intensity of light, inverse square
law photoelectric exposure meter
4.2.4
Light bulb brightness, Joly
photometer, wax-block photometer
27.4.1.1 Paraffin block photometer, Joly
diffusion photometer
Two large paraffin blocks with tin foil sandwiched in between make a
sensitive photometer. Use with lamps on either side. Two paraffin
blocks separated by an aluminium sheet are moved between two light
sources until they appear equally bright.
27.4.1.2 Grease spot photometer, Bunsen
grease spot photometer
A piece of paper with a grease spot is moved between two light sources
until the spot disappears. A grease spot disappears when illuminated
equally from both sides.
27.4.1.3 Rumford
shadow photometer
Light sources are moved until their shadows of the same object are of
equal intensity. Two light sources are moved so the shadow cast by a
vertical rod is of the same intensity.
27.4.1.4 Frosted globe surface brightness
The surface brightness of a 40 W bulb is compared to a frosted globe
placed over it.
27.4.1.5 Checker board
Use a point source to superimpose shadows of a rectangle and a 3h x 3w
checkerboard rectangle.
27.4.1.6 Inverse square law model
A wire frame pyramid connects areas of 1, 4, and 16 units.
27.4.1.7 Foot-candle meter
Use a Weston type foot-candle meter to measure the inverse square law.
27.4.1.8 Surface brightness of a lens
Place the eye at the image point of a lens focussed on a dim lamp.
27.4.1.9 Reflected surface brightness
With a bright spot at the object point of a concave mirror and the eye
at the image point the whole mirror seems to have the same surface
brightness as the spot.
27.4.2.1 Radiometer, quartz fibre radiometer
Focus a beam of light intermittently on a vane of the quartz fibre
radiometer at the frequency of oscillation.
27.4.3.1 Hole in a box, Bichsel boxes
Holes in black boxes are blacker than the boxes. Two black boxes have
blacker appearing holes in them. One box actually is painted white
inside.
27.4.3.2 Carbon block
A carbon block with a hole bored in it is heated red-hot with a torch.
The hole glows brighter. Bore a hole in an old carbon arc rod and heat
electrically. The hole glows brighter.
27.4.3.3 Radiation from a black body
See 23.8.0:
Heat
transferred by radiation, black
body radiation
Two holes are drilled in a carbon
block. One is filled with a porcelain
insulator and the block is heated red-hot with a torch. Graphite and
porcelain heated red-hot look the same. A pattern on a porcelain dish
shows brighter when heated.
27.4.3.4 Good absorbers good radiators
An electric element with chalk marks or china with a pattern are heated
until they glow.
27.4.3.5 Plotting the spectrum
Measure the output of a thermopile as it is moved across a spectrum.
Hold a thermopile connected to a galvanometer in different parts of a
spectrum. Use a thermopile and galvanometer to show the infrared energy
in the continuous spectrum.
27.4.3.6 Variac and light bulb
Vary the voltage to a 1 KW light bulb with a variac to show colour
change with temperature. Vary the voltage across a clear glass lamp
from zero to 50% over voltage Also measure the intensity and plot
against power.
27.5.0 Interference
Young's Experiment
Two point sources of "in phase" light produce an interference pattern
of nodes and antinodes just like two point dippers dipping in phase
into water of uniform depth in a ripple tank. The shorter the
wavelength, the more closely crammed is the interference pattern so the
pattern for violet light is more crammed than the pattern for red
light.
27.5.1.1 Making double slits
Photograph two dark wires against a white background with high contrast
film and use the negative for a double slit.
27.5.1.2 Double slit and laser
Shine a laser beam through double slits of different widths and
spacing. Pass a laser beam through double slits of different widths and
spacing. Direct a laser through a double slits of different dimensions.
Pass a laser beam through double slits on the Cornell slide.
27.5.1.3 Cylindrical tube interference
The ring pattern from shining a point source down a reflecting
cylindrical tube results from interference of two virtual sources.
27.5.1.4 Fresnel biprism
A laser through a Fresnel biprism gives two interference sources. A
Fresnel biprism is placed between a slit and projecting lens giving a
pattern similar to a double slit parallel to the laser beam translation
double slit wavefront. August-Jean Fresnel, 1788-1827, also invented
the lighthouse prism to
concentrate light from an oil lamp to form a beam. This prism is still
used in lighthouses around the world and in some traffic lights. A
conventional lens needed to focus the beam of a large lighthouse would
weigh tonnes and be inefficient. However, the Fresnel "all surface"
lenses do away with the useless middles of large lenses. Fresnel lenses
may be formed in a thin sheet of plastic. Fresnel also invented the
Fresnel
lantern containing prisms to produce a soft beam for for back light
stage lighting or front light orchestra lighting.
27.5.2.0 Gratings, interference of polarized
light, polarized sunglasses
Polarized light has the changing electric field component in one plane.
Polarizers, e.g. as in Polaroid sun glasses, allow only one plane of
changing electric field to pass through them to reduce glare caused by
light reflected from polarizing surfaces, e.g. water, snow and
sky radiation.
27.5.2.1
Drink-can spectroscope
Tape a replica grating over the hole cut a slit in the bottom. Make a
slit in the cover of a film canister and place a grating over a hole in
the bottom made with a No. 2 cork bore.
27.5.2.2 Two dimensional grating
View a motor car headlamp through a small square of silk.
27.5.2.3 Speckle patterns in unfiltered sun
Speckle patterns from sunlight scattered by a diffusing surface are
common. Train yourself to see them.
27.5.2.4 Number of slits
Shine a laser beam through various numbers of slits with the same
spacing.
27.5.2.5 Grating in air and water
Measure the pattern of a laser beam incident on a diffraction grating
placed inside an empty aquarium and with it full of water.
27.5.2.6 Babinet's principle
Carefully drawn black spots on white paper are photographically reduced
and the positive and negative copies are used as complementary arrays.
27.5.2.7 Random multiple gratings
Exhale on clean glass to produce random multiple gratings of water
droplets. Look through a drop of blood on a microscope slide at a point
source or project onto a screen from a point source. Dust a bathroom
mirror and hold a small light as close to the eye as possible. A
collimated beam of white light is passed through a glass dusted with
Lycopodium powder.
27.5.2.8 Speckle spots and random diffraction
The sparkling of a spot illuminated by a laser beam on the wall is
caused by random interference patterns caused by scattered light
speckle spots and random diffraction.
27.5.2.9 Speckle patterns in arc light
Speckle patterns can also be seen in arc lamp light The patterns
disappear as the object is brought closer to the arc.
27.5.3.1 Soap film interference
Reflect white light off a soap film onto a screen. Project white light
reflected off a soap film in a wire frame onto the wall. Illuminate a
soap film with an extended source in a darkened room
27.5.3.2 Newton's rings
Reflect white light off Newton's rings onto the wall. Reflect light off
a long focal length lens squeezed against a flat glass. Note change of
ring size with different coloured light.
27.5.3.3 Stable black soap films
Vidal Sasson Extra Gentle Formula makes black films lasting five
minutes or longer stable.
27.5.3.4 Constant soap film
Fit a large graduated cylinder with a rectangular frame with the
handle protruding through the stopper. Fill half full with soap
solution.
27.5.3.5 Boys rainbow cup
Rotate a hemispherical shell with a soap film across the front so the
black spot forms in the middle.
27.5.3.6 Air wedge
A sodium lamp illuminates an air wedge between two plates of glass.
Diffuse sodium light with frosted glass before reflecting it off
two plane glass plates. The diffused light from a high intensity sodium
lamp is viewed by reflection off one and two pieces of plate glass
glass plates in sodium light.
27.5.3.7 Mica interference
Examine interference by reflection of filtered mercury light from a
mica sheet onto a screen. Reflect light from a mercury point source off
a thin sheet of mica onto the opposite wall.
27.5.3.8 Turpentine film
White light incident of the surface of turpentine on water at an angle
of 45-60 degrees is focussed on a screen.
27.5.3.9 Absorption phase shift
Cover the back of a microscope slide with streaks of an absorbing dye
and observe under monochromatic.
27.5.3.10 Tempering colours
A thin film of oxide forms on a polished steel sheet when it is heated.
27.5.3.11 Oil film
The thickness of a film of oil on a pan of water that can be
varied by sliding an iron bar across the surface for a variable
interference filter.
27.5.4.1 Michelson interferometer
Use a Michelson interferometer with either laser or white light.
Project coloured fringes from white light onto a screen insert a hot
object in one path. Measure the power of solar cells in the two outputs
of the Michelson interferometer.
27.6.1.1 Polaroids on the overhead
Examine polarization with two sheets of Polaroid and a pair of
sunglasses on an overhead projector. Two Polaroid sheets are partially
overlapped while aligned and at 90 degrees.
27.6.1.2 Polarization mechanical model
A pendulum is hung from a long strut restrained by slack cords.
Circular motion of the pendulum will be damped into a line by the
motion of the strut.
27.6.1.3 Polaroids cut at 45 degrees
Cut squares of Polaroid so the axes are at 45 degrees. Now turning one
upside down causes cancellation.
27.6.2.1 Making black glass
See 2.4:
Canada balsam
Eliminate the reflection off the second surface of a glass plate with a
Canada balsam and lampblack suspension on the back side.
27.6.2.2 Brewster's angle
Rotate a Polaroid filter in a beam that reflects at Brewster's angle
off a glass onto a screen. A beam of white light is reflected off
a sheet of black glass at Brewster's angle onto the wall. Use
a Polaroid to test Brewster's angle.
27.6.2.3 Tilt the windowpane
Reflect plane polarized light off a window pane and vary the angle of
incidence through Brewster's angle.
27.6.2.4 Stack of plates
A stack of glass plated at 57 degrees will transmit and reflect light
that is cross polarized.
27.6.3.1 Laser and quinine sulfate, tonic water
Pass a polarized laser beam through a cylinder filled with a quinine
sulfate solution.
27.6.3.2 Rotation by sugar solution
Insert a tube of sugar solution between crossed Polaroids. Compare the
rotation of plane polarized light in tanks containing sugar solution,
turpentine and water.
27.6.3.3 Three Polaroids
Use 3 sheets of Polaroid on an overhead projector.
27.6.3.4 Rotation by polarizing filter
Stick a third sheet between crossed Polaroids.
27.6.3.5 Barber pole
A beam of polarized light is rotated when directed up a vertical tube
filled with sugar solution. Examine a beam of polarized light up
through a tube with a sugar solution and scattering centres The beam
rotates and colours are separated.
27.6.3.6 Barbershop sugar tube
Illuminate a tube of corn syrup from the bottom. Insert and rotate a
Polaroid filter between the light and tube.
27.6.3.7 Faraday rotation
Insert a partially filled glass container of wax into the core of a
solenoid between crossed Polaroids.
27.6.4 Birefringence
Birefringence is having a different refractive index for light in
different directions.
27.6.4.1 Calcite
crystals
Use a second calcite crystal to show the polarization of the ordinary
and extraordinary rays. Rotate a calcite crystal on an overhead
projector covered except for a small hole Use a Polaroid sheet to check
polarity. Rotate a calcite crystal with one beam entering and two will
emerge one on axis and the other rotating around ordinary and
extraordinary ray.
L-birefringent crystal
Project a hole in a strongly
illuminated cardboard onto a screen through a calcite crystal.
Interpose and rotate a polarizing plate to make the two images
disappear alternately. Place a calcite crystal over printed material or
a metal plate.
27.6.4.2 Plexiglass birefringence
Examine birefringence of a Plexiglas rod directly with a linearly
polarized laser.
27.6.4.3 Pendulum model
Strike a pendulum with a blow then wait 1 / 4, ½ or 3 / 4 period
and
strike another equal blow at right angles to the first.
27.6.4.4 Model of double refraction
A double pendulum displaced in an oblique direction will move in a
curved orbit.
27.6.4.5 Wavefront models
See 2.0.5: Conic sections, ellipse
Wire models show spherical and elliptical wavefronts in crystals.
27.6.4.6 Nichol prism
One of a pair of Nichol prisms is rotated as a beam of light from an
arc lamp is projected through Nichol prism.
27.6.4.7 Crystal structure of ice
A thin slab of ice is placed between crossed Polaroids crystal.
27.6.4.8 Colour with mica
Rotate a mica sheet between crossed Polaroids colour with mica
quartz wedge.
27.6.4.9 Birefringent clear plastics
Doubly refraction material includes the following:
1. A crispy transparent cellophane
wrapping for confectionery, potato chips and computer disk packets
2. Clear polystyrene rectangle from a window envelope
3. Polyethylene terephthalate (PET) soft drink bottle side.
Place a square
cut from doubly refraction material between fixed and rotateable
Polaroid sheets crossed so that transmitted light is
extinguished. The 3 materials together let light pass through again!
PET bottles used to have a second black polyethylene as a cup on the
bottom for a strong base but now have a bottom with five convolutions.
PET is a birefringent 2-dimensional orientated plastic. A birefringent
material has a different refractive index in the two dimensions, that
is, a different speed for left-handed and right-handed helixes, slowing
one
down with respect to the other. When polarized light passes through,
this differential results in a rotation of the plane of polarization.
So crossed Polaroids are no longer crossed when material in between has
caused a rotation. The amount of rotation depends on the degree of
orientation of the polymer molecules and thickness of the film.
27.6.5.1 Sunset with polarizer
Use a sheet of Polaroid to check the polarization of scattering from a
beam of light passing through a tank of water with scattering
particles. Rotate a Polaroid in the incoming beam or at the top and
side of the tank in the sunset demonstration.
27.6.5.2 Tyndall experiment
Shine light in one side of a box with a scattering solution and look at
the scattered light out in a perpendicular direction.
27.6.5.3 Polarization by scattering
Add milk to water and show polarization of light scattered from a beam.
27.6.5.4 Haidinger's brush
Train yourself to detect polarized light with the naked eye.
27.2.0 Visible spectrum, rainbow
Sunlight through
prism, recombining spectrum, rainbow, spectroscope, electromagnetic
spectrum
The spectrum is the arrangement of frequencies or wavelengths when
electromagnetic radiation are separated into their constituent parts.
Visible light is part of the electromagnetic spectrum and most sources
emit waves over a range of wavelengths that can be broken up or
"dispersed". White light can be separated into the seven colours of the
spectrum: red, orange, yellow,
green, blue, indigo, and violet, also called the fundamental colours.
27.7.0 Modern optics,
holography, physical optics, photoelectric effect
Photoelectric effect
The photoelectric effect is the loss of electrons from a metal surface
due to electromagnetic radiation hitting the surface. A "particle" of
light or photon has a specific amount of energy called a quantum of
energy. Photons of light of higher energy have higher frequency, v, and
shorter wavelength, X. Photocell (vacuum type) Threshold frequency is
the minimum frequency of radiation which will just produce the
photoelectric effect and is different for different metals, e.g.
Magnesium has a lower threshold frequency than copper so it is a more
sensitive. Photoelectric cells can produce electricity.
28.12.0 The eye, structure and physiology
Blind spot, binocular vision, defects, spectacles and contact lenses,
persistence of vision
28.12.1 Model of the eye
Examine a take apart model of the eye.
28.12.2 Water flask model of the eye
A large flask filled with water, fluorescein and with external lenses
make a model of the eye in near-sighted and far-sighted conditions. A
spherical lens filled with milky water represents the eyeball. Use a
large lens in front of the sphere to show inverted image near and far
sightedness.
28.12.3 Blind spot
Move a white cross towards a white spot on the blackboard with one eye
closed.
28.12.4 Inversion of image on retina
A small tube has three holes in a triangular pattern drilled in one end
and a single hole in the other. Hold the triangular end near the eye
and the pattern appears inverted.
28.12.5 Astigmatism
Look at a chart of radial black lines.
28.12.6 Eyeglasses
Project an image of concentric circles crossed by radial lines. Place a
lens and then a correcting lens over the projection lens.
28.12.7 Chromatic aberration of the eye
A purple filter is mounted in front of a straight filament lamp.
28.12.8 Resolving power of the eye
The limit of resolving two filaments of an auto headlamp is about 10 m.
28.12.9 Retinal fatigue colour
A red light placed behind a rotating with a slot at the border of
half black and half white appears different colours depending on the
direction of rotation. A disc with a notch half black half white is
spun in front of a red lamp The lamp appears green or red depending on
the direction that the disc spins. A black and white patterned
disc appears coloured when rotated.
28.12.10 Fluorescence of retina
Shine an UV source with a visible filter towards the class and notice
the luminous haze that covers the field of view.
28.12.11 Jarring the eye
Stamp your foot while watching a free running oscilloscope.
28.12.12 Subjectivity of colours
A red spot projected on the wall looks orange or brown if it is
surrounded by white or black.
28.12.13 Mach disc
A spinning disc appears to have light and dark rings where it should be
uniform
28.12.14 Most sensitive to green light
A stick moved up and down in a projected spectrum will appear to bend
at the green light are most sensitive to green light
28.12.15 Impossible triangles
An optical illusion that depends on viewing angle.
28.12.16 Square that is not there
See diagram 28.1.1.7: Absent square
1. The human brain tries to make sense of all sense perceptions, even
to "seeing" a square that is not there!
2. A cut-out square in
black paper has the illusion of being a white square on top of black
paper.
28.12.17 Optical illusions
Compare the height to the width of a projected hat.
28.12.18 Colour blindness
Use standard colour blindness slides or charts to test for colour
blindness.