Light 3
92
Light Seán Finn Department of Education UCC
description
Science Realted facts on LIGHT for Primary School 5th/6th Class
Transcript of Light 3
Light
Seán Finn
Department of Education
UCC
Light sources.All of these objects can be seen in the dark because they let out their own light-they are
luminous
How do we see objects that do not let out their own light i.e. non luminous bodies?
• We can see them when light from another source reflects from them.
• We will not be able to see these objects in the dark.
Killarney by night
Light travels from a source
When it is ABSOLUTELY DARK
you cannot see anything at all
When it is ABSOLUTELY DARK
you cannot see anything at all
There might be something HERE …
There might be something HERE …
…but you cannot see it
…but you cannot see it
Light travels from a source
…bounces off it and travels to your EYEEYE……bounces off it and travels to your EYEEYE…
But in the daylight RAYS OF LIGHTRAYS OF LIGHT from
the SUNSUN travel to this object…
But in the daylight RAYS OF LIGHTRAYS OF LIGHT from
the SUNSUN travel to this object…
…and NOWNOW you can see it
…and NOWNOW you can see it
Light travels from a sourceThere are actually many RAYS RAYS
OF LIGHTOF LIGHT bouncing off the object but the diagrams
become too complicated if you put them all in
There are actually many RAYS RAYS OF LIGHTOF LIGHT bouncing off the object but the diagrams
become too complicated if you put them all in
Do all substances allow light to pass through them?
Light will not pass through substances like aluminium foil.
Light will pass easily through substances like glass
Some light will pass through certain substances
Opaque materials do not allow light to pass through them.
Transparent materials
Light will pass very easily through some
materials
Light will pass very easily through some
materials
cling filmcling film
glass windowglass windowplastic bottleplastic bottle
They are said to be TRANSPARENTThey are said to be TRANSPARENT
Translucent materialsYou cannot SEE
through a sheet of greaseproof paper like you can see through glass
You cannot SEE through a sheet of greaseproof paper like you can see through glass
But if you shine a torch behind the
greaseproof paper you can see the light but NOT exactly what the
torch looks like
But if you shine a torch behind the
greaseproof paper you can see the light but NOT exactly what the
torch looks like
Design and make a model glasshouse using a plastic bottle that will allow
light to pass through
A cloche
Place thermometer in bottle next to light. Note that the temperature of the air in the bottle increases.
Investigation: Light travels in straight lines.
A
B
C
How light travels…you can see the view out of the other
end
…you can see the view out of the other
end
If you look through a
long cardboard
tube…
If you look through a
long cardboard
tube…
How light travels…you cannot see anything
out of the other end
…you cannot see anything
out of the other end
If you bend the cardboard tube and then look through
it…
If you bend the cardboard tube and then look through
it…
How light travelsThis is because light travels in
STRAIGHT LINES
This is because light travels in
STRAIGHT LINES
In this tube there is a straight line from one end to
the other
In this tube there is a straight line from one end to
the other
In this tube there is only a straight line UP TO HERE
In this tube there is only a straight line UP TO HERE
The light CANNOT go any further
The light CANNOT go any further
How shadows are formedThere many of rays of light travelling in
STRAIGHT LINESSTRAIGHT LINES from the torch
There many of rays of light travelling in
STRAIGHT LINESSTRAIGHT LINES from the torch
Some travel PASTPAST the ornament….
Some travel PASTPAST the ornament….
…but others “BUMP BUMP INTOINTO” the ornament and cannot travel
any further
…but others “BUMP BUMP INTOINTO” the ornament and cannot travel
any further
Formation of shadows
torchtorch
the OBJECTOBJECT is blocking the
light here
the OBJECTOBJECT is blocking the
light here
Light from the torch travelling in a straight line CANNOT CANNOT get
behind the OBJECTOBJECT
Light from the torch travelling in a straight line CANNOT CANNOT get
behind the OBJECTOBJECT
OBJECTOBJECTOBJECTOBJECT SHADOWSHADOW on wall
SHADOWSHADOW on wall
Size of shadowsIf light was able to travel in
CURVESCURVES then we would not get SHADOWSSHADOWS
If light was able to travel in CURVESCURVES then we would not get
SHADOWSSHADOWS
BUT LIGHT ONLY
TRAVELS IN
STRAIGHT LINES
BUT LIGHT ONLY
TRAVELS IN
STRAIGHT LINES
Size of shadows
As the toy is moved towards the wall the shadow gets
smaller
As the toy is moved towards the wall the shadow gets
smaller
shadow getting smaller
shadow getting smaller
Size of shadows
shadow getting smaller
shadow getting smaller
Size of shadows
shadow getting smaller
shadow getting smaller
Size of shadows
shadow getting smaller
shadow getting smaller
Size of shadows
LARGE SHADOW when the toy is
close to the light
LARGE SHADOW when the toy is
close to the light
SMALLER SHADOW when
the toy is further from the
light
SMALLER SHADOW when
the toy is further from the
light
TINY SHADOW when the toy is a long way from
the light
TINY SHADOW when the toy is a long way from
the light
Formation of shadows
By using a mixture of opaque, translucent
and transparent materials you can create shapes to produce shadow
puppets
By using a mixture of opaque, translucent
and transparent materials you can create shapes to produce shadow
puppets
Shadow puppetsShadow puppets
Here a simple cardboard shape (opaque) has holes made in it
(transparent) to provide eyes and a mouth
Here a simple cardboard shape (opaque) has holes made in it
(transparent) to provide eyes and a mouth
This is a picture of a very complicated shadow puppet
This is a picture of a very complicated shadow puppet
It is made from opaque wire and transparent
materials that are also coloured giving the
shadow produced a very colourful appearance
It is made from opaque wire and transparent
materials that are also coloured giving the
shadow produced a very colourful appearance
Shadow puppetsShadow puppets
Shadows from the sunHere you can see
shadows formed outside by the SUN
Here you can see shadows formed outside
by the SUN
Notice that the shadows are different sizes at
different times of the day
Notice that the shadows are different sizes at
different times of the day
SHORT, VERY DARK shadowSHORT, VERY DARK shadow
LONG, LIGHTER shadow
LONG, LIGHTER shadow
Shadows from the sunTo see how
shadows change during the day
stand in a FIXED position and then get someone to draw round your
shadow using chalk or water-
based paint
To see how shadows change during the day
stand in a FIXED position and then get someone to draw round your
shadow using chalk or water-
based paintA few hours later stand in EXACTLY the same place and again get
some one to draw around your
shadow
A few hours later stand in EXACTLY the same place and again get
some one to draw around your
shadow
Shadows from the sun
This will show you how much shadows change over a few
hours
This will show you how much shadows change over a few
hours
To see how shadows change during the day
stand in a FIXED position and then get someone to draw round your
shadow using chalk or water-
based paint
To see how shadows change during the day
stand in a FIXED position and then get someone to draw round your
shadow using chalk or water-
based paintA few hours later stand in EXACTLY the same place and again get
some one to draw around your
shadow
A few hours later stand in EXACTLY the same place and again get
some one to draw around your
shadow
Measuring shadowsMeasuring shadows
Measuring the length of shadows
On a SUNNY day set up a stick on a clear piece of
ground
On a SUNNY day set up a stick on a clear piece of
ground
Using a ruler CAREFULLY measure the length of
the shadow
Using a ruler CAREFULLY measure the length of
the shadow
Notice what time it is and then record your
result in a table like this
Notice what time it is and then record your
result in a table like this
Table of results
Time Length of shadow
9.00 am 47 cm
10.00 am
11.00 am
12.00 noon
1.00 pm
2.00 pm
3.00 pm
4.00 pm
EVERY HOUR go back to the stick
and again measure the length of the
shadow
EVERY HOUR go back to the stick
and again measure the length of the
shadow
Size of shadows10.00
am10.00
am12.00 noon12.00 noon
2.00 pm2.00 pm 4.00 pm4.00 pm
Table of resultsTime Length of
shadow
9.00 am 47 cm
10.00 am 43 cm
11.00 am 37 cm
12.00 noon 22 cm
1.00 pm 35 cm
2.00 pm 42 cm
3.00 pm 45 cm
4.00 pm 49 cm
These results can then be put into a
BAR CHART to help you see a
PATTERN in your results
These results can then be put into a
BAR CHART to help you see a
PATTERN in your results
Shadows during the day
0
5
10
15
20
25
30
35
40
45
50
Length
of
shadow
(cm
s)
9 am 10 am 11 am 12 noon 1 pm 2 pm 3 pm 4 pm
Time
The bar chart shows that the shadow is shortest at 12
noon
The bar chart shows that the shadow is shortest at 12
noon
Light and dark
The light is broken up into dark and
light stripes
The light is broken up into dark and
light stripes
This is a ray of light
shining from a torch
This is a ray of light
shining from a torch
Put a comb in front of
the torch
Put a comb in front of
the torch
The comb lets light through the gaps,
but stops it passing through the prongs
The comb lets light through the gaps,
but stops it passing through the prongs
Day and night
The Earth moves, the Sun stays stillThis is the
SunThis is the
Sun
This is the EARTH looking down on the
Arctic
This is the EARTH looking down on the
Arctic
These are the rays from the
SUN lighting up the EARTH
These are the rays from the
SUN lighting up the EARTH
This is the half of the Earth that light
from the Sun reaches - DAY
This is the half of the Earth that light
from the Sun reaches - DAY
This is the half that light from the Sun does NOT reach -
NIGHT
This is the half that light from the Sun does NOT reach -
NIGHT
The sun gives us heat and light without which we could not live
Experiment: To make a solar panel
Perspex sheet
Water
Thermometer
Light is made up of seven colors. -The spectrum
Making a spectrum
Making a spectrum
Making a spectrum
Not all objects reflect light.
• Black objects absorb all light and do not reflect any.
• White objects reflect all light
• Red objects absorb blue and green light and reflect red light.
Reflection
• We see most objects because they reflect light.
• Most objects reflect light is a diffuse way.
• In some objects that are smooth and opaque regular reflection occurs.
Activity: To investigate reflection
• Place mirror on white paper.
• Shine a ray into the mirror at an angle.
• Note the position of the reflected ray.
• Change the angle at that the ray makes by moving the light box.
Ray box
Mirror
The periscope
Two mirrors parallel to each
other at 450
Making a periscope
Curved mirrors
Concave mirrorConcave mirors can produce images that are right way up or upside down also larger or smaller. If you place your face close to the mirror your image will by magnified and right way up.
Use: Shaving and make-up mirrors
Convex mirrors
• Always produce an image that is right way up and diminished.
• They are used seeing around corners and in shops for security.
Refraction
To investigate refraction• Shine a ray of light through a glass block at
an angle.
• Look at the ray of light in the glass from above.
• Increase the angle between the glass and the ray box.
• What do you notice?
Why does refraction occur?
Refraction
To investigate refration in a liquid
Explore how objects may be magnified using simple lens or magnifier
Lenses opperate due to refraction
Use of lenses
• Camera
• Telescope
• Binoculars
• Glasses
• Microscopes
The telescope• Two convex lenses, the
objective and the eyepiece.• Eyepiece has a short focal
length• Objective has a long focal
length• Object to be observed at
least 10 m away.• Telescope has to be
focused by varying distance between lenses (sum of focal lengths)
• Magnification is the ratio of focal lengths
Be aware of the dangers of excessive
sunlight dangers of looking directly at the sun effect of the
sun’s rays on skin•Sunlight contains ultra-violet (UV)light.
•If sunlight enters the eye it will kill the cells of the retina. These will not grow back.
•. UV light on the skin causes sunburn and aging of the skin and may caues skin cancer.
•Suncream absorbs UV light
The telescope
Design and make model telescopes
Tubing
Plastic wrap
Appreciate the importance of sight
The iris controlls the amount of
light entering the eye
Bright Dark
Structure of the eye
The lense of the eye
focuses light onto the retina
which is carried to the brain via the optic nerve
Understand the role of sunlight inphotosynthesis
• Plants make their own food using sunlight in a process called photosnthesis.
• Without light plants cannot grow.• We eat plants for food or we eat animals/ animal products that
have eaten plants.
Why the Moon seems to changeWhy the Moon seems to change
The MOON looks different depending on where it is
in relation to the SUN
The MOON looks different depending on where it is
in relation to the SUN
From the Earth you cannot see any light
hitting the Moon in this position
From the Earth you cannot see any light
hitting the Moon in this position
New MoonNew Moon
This is what the Moon looks like
from Earth
This is what the Moon looks like
from Earth
Waxing crescentWaxing crescent
This is what the Moon looks like
from Earth
This is what the Moon looks like
from Earth
Why the Moon seems to changeWhy the Moon seems to change
Last quarter
Last quarter
This is what the Moon looks like
from Earth
This is what the Moon looks like
from Earth
Why the Moon seems to changeWhy the Moon seems to change
Waxing gibbousWaxing gibbous
This is what the Moon looks like
from Earth
This is what the Moon looks like
from Earth
Why the Moon seems to changeWhy the Moon seems to change
Full MoonFull Moon
This is what the Moon looks like
from Earth
This is what the Moon looks like
from Earth
Why the Moon seems to changeWhy the Moon seems to change
Waning gibbousWaning gibbous
This is what the Moon looks like
from Earth
This is what the Moon looks like
from Earth
Why the Moon seems to changeWhy the Moon seems to change
Waning crescentWaning crescent
This is what the Moon looks like
from Earth
This is what the Moon looks like
from Earth
Why the Moon seems to changeWhy the Moon seems to change
To demonstrate why the shape of the Moon changes
Solar Eclipse
Lunar Eclipse
It is VERY DANGEROUS to
look DIRECTLY at the Sun or at a
REFLECTION of the Sun – it could make
you BLIND
Infants and Junior Classes (Teacher guidelines)
• Identify different light sources
• Explore the effect of light on materials
• Identify materials that are transparent or opaque.
• Experiment with shadows and reflections
Middle and senior classes (Teacher guidelines)
• Distinguish between natural and artificial sources of light.
• Explore that white light is made up of many different colours.
• Investigate how light rays change direction as they pass through water and learn that this process is called refraction.
• Understand that mirrors and other shiney surfaces can change the direction of light.
• Explore how lenses are used to make things look bigger and smaller.
Science Curriculum.Infant and Junior Classes
Science Curriculum.First and second classes
Science Curriculum.Third and fourth classes
Science Curriculum.Fifth and sixth classes
