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Light
Reflection and Refraction
Learning Outcomes
OP33 understand that light is a form of energy
and that it can be converted to other
forms
OP34 show that light travels in straight lines and
explain how shadows are formed
OP35 understand that luminous objects are a
source of light while non-luminous objects
are seen as a result of light reflected from
them
Lessons
Learning Outcomes
OP36 Recall that white light is made up of
different colours which can be separated
by dispersion
OP37 Produce a spectrum of white light using
appropriate apparatus, and list the
colours of the spectrum.
Lessons
Learning Outcomes
OP38 investigate the reflection of light by plane
mirrors, and illustrate this using ray
diagrams; demonstrate and explain the
operation of a simple periscope
OP39 show the refraction of light as it passes
from: air to glass, air to water, glass to air,
water to air; show refraction of light
through a lens; demonstrate the
operation of a magnifying glass
Lessons
Light is a Form of Energy
• ‘the’ source of energy for plants
• Indirect source of energy for animals
Light Energy
Conversion of Light Energy
Light  kinetic energy
Crookes Radiometer
Light  Electrical Energy
Luminous/Non-Luminous Bodies
• An object is seen when light from it reaches eyes
• Luminous objects give out light
• Non-luminous objects don’t give out light
• How can we see non-luminous objects?
• Sources of light – luminous objects
– Sun, stars, candle, lamp, fire and other chemical reactions
Seeing Non-Luminous Objects
luminous
object
Nonluminous
object
Transmission of Light
• Light travels in straight lines
• Can you give examples?
Grand Central Station, New York
To Show That Light Travels in
Straight Lines
cardboard
light
bulb
thread/string
Mandatory Practical
To Show the Formation of Shadows
White Sheet/Cardboard
Object
Torch
This also shows that
light travels in straight
lines.
Mandatory Practical
Light Speed
• 300 million metres per second (3x108 m/s)
• Sun  Earth (150million miles)
– takes ~8 minutes
• Light year – distance light travels in 1 year
– How many seconds in a year?
• Answer: 9,460,000,000,000km
Reflection
• Practically all surfaces reflect light
– Shiny smooth surfaces have regular reflection
– Matt (dull) surfaces have scattered reflection
Uses of Reflection
• What are some uses of reflection?
– Mirror, periscope (used in submarines)
mirror at 45o angle
Periscope
To show reflection of light by a plane mirror and to
demonstrate the operation of a periscope
light box
light box
bulb inside box
sheet
pencil mark
mirror
mirror
From the top
Mandatory Practical
Refraction of Light
• Why do objects appear contorted under water?
• Why does a swimming pool look shallower than it really is?
• Light travels in straight lines through air, glass, water etc.
• BUT
• When it passes from one to the other it changes direction.
Refraction is the bending of light from one medium to another
Refraction Demonstration
light box
sheet
refraction from
air to glass
occurs here
glass block
Plan view of experiment to demonstrate refraction
Lenses
• Simple optical devices
• Curved surfaces use refraction to focus
• Convex/converging lens (fat in the middle)
Example: magnifying glass
• Concave/diverging lens (thin in the middle)
Example: lenses of short sighted people
Spectrum of White Light
Spectrum of Light
• Where do the colours of the rainbow come from?
• Are they always the same colours?
• YES!
Colour Spectrum
Red, Orange, Yellow, Green, Blue, Indigo and Violet
• The name given to the splitting up of white light
into its separate colours is dispersion
Producing a Colour Spectrum
light box
bulb inside box
Colour Spectrum
Red, Orange,
Yellow, Green,
Blue, Indigo,
Violet
prism
paper or
card
screen
Homework Suggestions
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Why is the sky blue?
Why are sunsets orange?
Why is sunburn more likely to occur if you are up a high mountain or at the
beach?
How do photosensitive sunglasses work?
Why are soap bubbles coloured in white light?
Why are compact discs coloured?
Why are sunglasses of particular benefit to fishermen?
How would a rainbow appear to passengers in an aeroplane when there is
rain in the air above and below them?
Why do materials purchased in a shop appear a different colour in daylight?
How does the eye see colour?
What causes after images and what colour are they?
If black is a good absorber of heat, why do Bedouins wear black robes in
the hot desert?
Why is the filament of an electric light bulb coiled?
Why is a firefly a more efficient light producer than a filament lamp?
Light Cloze Test A
• Light is a form of ______. In a piece of
apparatus called a ______, light energy is
converted to ______ energy, and in the process
of photosynthesis it is converted to ______
energy. Animals get energy ______ from this
process. Light travels in ______ lines, but it can
be made to change direction in two ways by
______ and ______. When light strikes a mirror
it is ______ and when it enters a glass block it is
______.
Light Cloze Test B
• Light, on being passed through a ______, is split
up into its component colours. This process is
known as ______ and the band of colours which
is formed is called a ______. The colours are
red, ______, ______, ______, ______, ______,
______. When all of these colours are
recombined, ______ light is produced. This
property of light was discovered by a scientist
named ______. An example of real-life
dispersion is a ______.
Light Cloze Test C
• An experiment to show that light travels in ______ lines
includes a light box, ______ sheets with a ______ in the
centre, a piece of ______ used to align the sheets and a
______ as a source of light. If the sheets are not-aligned
the viewer sees ______ and if they are aligned the
viewer sees ______.
• To see the effect of shadows you require:
______, ______ and a ______
When the torch is turned on in a darkened environment
the dark______ of the object appears on the ______.
• A light box, sheet, screen and a ______ ______ are
required to show refraction from ______ to glass. To
indicate ______, a triangular glass block known as a
______ is required which disperses the light and
produces a ______ ______.
Light Cloze Test D
• A ______ glass is an example of a convex or
______ lens. This causes _____ rays to ______
at a point. The opposite type of lens is ______ in
the middle and is know as a ______ lens. This
causes light rays to ______ and is used in the
glasses of ______ sighted people.
• If confronted by a tall wall, a ______ would
enable you to see over it. They are more
commonly found in ______ to see ______ the
water surface. This works by placing ______
mirrors at an angle of ______.
Resources
• Images
• http://acept.la.asu.edu/PiN/mod/light/reflection/pattLight1Obj1.html
• http://science-education.pppl.gov/SummerInst/auroraborealis.jpg
• Information
– Diagram & Info on Crooks Radiometer
•
http://www.teachersparadise.com/ency/en/wikipedia/c/cr/crookes_radiometer.html
– Did you know questions for light
• www.juniorscience.ie/jsss/Main/3B3R.htm
– Syllabus information
• www.education.ie
– Info on light, reflection & refraction
• http://acept.la.asu.edu/PiN/mod/light/reflection/pattLight1.html
• Science Today, Physics Textbook
• Sounds
– Farm noises
• http://www.grsites.com/sounds/farm001.shtml