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| Light Experiments |
Darren Dowling
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| Materials Required |
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Card.
Bowl of water.
Comb.
Clear polythene bag or clear tape
Protractor.
Pencil.
Cardboard tube.
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Torch.
Compass.
Sellotape
2 Mirrors.
Glass of water.
Magnifying glass.
Coin.
Long, thin box
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| Quick Links |
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| Downloads |
Darren Dowling
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| Light & Shadows |
Darren Dowling
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| Light can pass through some substances,
such as glass or water. These are called transparent and we
can see through them Other substances, such as paper and metal,
stop light passing through. They are called opaque. Shadows
appear behind opaque substances when light shines on them. Shadows
are produced because light travels in straight lines and cannot
bend around corners. |
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| Shadow Clocks |
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Equipment: A long, thin box, pencils, tape, white paper.
Method: Cover one side of the box with white paper and hold
it in place with sticky tape. Stick a pencil across the end
of the box. On a sunny morning, take your shadow clock outside
and place it on a pale- coloured, flat surface (such as a
sheet of white paper). Point the box in the direction of the
Sun. Notice where the shadow of the pencil falls and draw
a line at the same point on the top of the box. Write the
time next to the line. Do this at several different times
during the day.
Expected Result: You should be able to make several different
marks down the length of the box during the day.
Explanation: As the Sun changes position in the sky, it casts
a different shadow at different times of the day
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| Make a Sundial |
Darren Dowling
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Equipment: Thin card, protractor, compass, piece of thick
cardboard.
Method: On the thin card, draw a right angled triangle. Make
the other two angles 45° (ideally the angle between the
board and the slope should be the latitude of your town to
make an accurate sundial). The two shorter sides should be
about 15cm long. Make sure to cut an extra flap
at the bottom of the dial to hold it upright on the board.
Draw a semi-circle on the cardboard. Stick the folded part
of the triangle firmly to the cardboard. Place the sundial
in a flat place outside so that the triangle points north-south.
Mark the position of the shadow that falls on the base every
hour.
Expected Result: You should find that the shadow travels the
same distance along the semi-circle every hour. On a sunny
day you will now be able to tell the time by looking at the
position of the shadow on your sundial.
Explanation: As the Sun changes position in the sky, it casts
a different shadow at different times of the day.
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| Reflections |
Darren Dowling
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| When rays of light
hit a surface or an object they bounce off again. This is called
reflection. Look for reflections in tin foil, cans, bottles
and spoons. You will find that flat, shiny surfaces produce
the best reflections. This is why most mirrors are made of flat
sheets of highly polished glass with a shiny silver coating
behind them. |
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| Investigating Reflections |
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Equipment: Comb, black paper, white paper, torch, mirror.
Method: Cut a small holes in a piece of card and tape a comb
across the hole. In a darkened room, place the card in front
of the torch, so that narrow beams of light come through the
teeth of the comb. Hold a mirror in the beams of light so
that it reflects the light. Move the mirror to a different
angle, what happens to the beams of light?
Expected Result: The angle of the reflected rays will change.
Explanation: Light is reflected off the mirror at exactly
the same angle as it hits the mirror.
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| More and More Reflections |
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Equipment: Two mirrors
Method: Stand two mirrors side by side and put a small object
between them. How many reflections can you see? Move the mirrors
closer together and then further apart. What happens to the
number of reflections? Place two mirrors facing each other
with an object between them. What can you see now?
Expected Result: As the mirrors move to face each other, you
will see more and more reflections. When they are opposite
each other, you should be able to see endless reflections.
Explanation: Less and less light is actually escaping
the two mirrors, so that when they are facing each other,
all the light is trapped in bouncing between the
two mirrors.
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| Bending Light |
Darren Dowling
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| Light travels at different
speeds through different substances. It travels more slowly
through water or glass than it does through air. As the light
slows down, it also changes direction a little. This is called
refraction and it makes the light rays look as if they bend
at the point where two substances meet. |
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| Magic Money |
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Equipment: A coin, bowl, water.
Method: Put the bowl on a table and place the coin in the
bottom. Keep looking at the coin and move slowly backwards
until the coin disappears from view. Stay standing in the
same place and ask a friend to pour water into the bowl. What
can you see?
Expected Result: You will find that you can see the coin again!
Explanation: The light from the coin is bent (refracted)
by the water so you can see it again.
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| Swimming pools and ponds never
look as deep as they really are because light from the bottom
is refracted before it reaches our eyes.
On a very hot day, you can sometimes see what looks like
a pool of water on the road although the road is really completely
dry. Light from the sky is bent (refracted) by
the hot air near the road and the pool you see
is actually refracted sunlight. This is why people see mirages
in a desert. The hot air bends the light so objects that are
really a long way away appear to be close by.
If you hold a pencil behind a thick glass dish so that half
the pencil is above the dish and half is below, you will find
that the part of the pencil behind the glass seems to be separated
from the part of the pencil in the air. This is because light
travels more slowly in glass than in air. The light rays change
direction at the edge of the glass and make a pencil look
as if it bends in the middle.
Glass can be made into different shapes so that it bends
the light in different directions. These are lenses.
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| Lenses |
Darren Dowling
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| Transparent materials
(such as water or glass), which can bend light rays by refraction,
can work as lenses. Lenses are curved on one or both sides and
are useful for bending light in special ways. They make objects
look larger or smaller, depending on the shape of the lens.
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| Making a Magnifying Glass |
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Equipment: Stiff cardboard, pencil,
clear polythene bag or clear tape, tape.
Method: Draw the shape of a magnifying
glass on the cardboard. Cut around the outline and cut out
a circle from the middle. Cut apiece of polythene to fit the
hole in the middle. Carefully stretch the polythene tightly
over the hole and secure it with sellotape. Put a drop of
water on to the polythene and hold the lens over a page in
a book.
Expected Result: You will see that
you have made a magnifying glass.
Explanation: The drop of water is
acting as a magnifier.
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| How Lenses Work |
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Equipment: White paper, card, comb, convex lens (magnifying
glass), concave lens (spectacles-short sighted), torch
Method: Cut a hole in the card and tape the comb over it.
In a darkened room shine a torch through the hole, so that
the rays of light shine over the paper. Hold the magnifying
glass against the edge of the paper and notice what happens
to the rays of light. repeat with a concave lens.
Expected Result: The magnifying glass will focus the rays
to a point, and the concave lens will spread the
rays of light out like a fan.
Explanation: The lenses are created so that light is refracted
in a certain direction.
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| Light & Sight |
Darren Dowling
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| When your eyes are open, the
light reflected from objects around you enters your eyes through
the pupil - the black hole in the middle. The pupil is an opening
in the coloured part of the eye which is called the iris. A
lens behind the iris focusses the light onto a light- sensitive
layer called the retina at the back of the eye. Special optical
nerves carry messages from the retina to the brain, which interprets
the images so you can see.
Because you have two eye you see two images of everything
you look at. Each eye looks at the world around you from a
slightly different position. This allows you to see things
in three dimensions rather than just as a flat picture. It
also helps you to judge distances and appreciate perspective.
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| How Many Pencils? |
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Equipment: Pencil, glass of water.
Method: Place a glass of water of a table and stand a pencil
about a foot behind it. Look through the jar and you will
see the images of two pencils in it. Close your left eye and
the right hand pencil will disappear. Close your right eye
and the left hand pencil will disappear.
Expected Result: The water is working as a lens to produce
the images but because the water is held in a cylinder shape
each eye looks through the water at a slightly different angle.
So , with both eyes open, you see two pencils. With one eye
open you see only one image.
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| Hole in the Hand |
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Equipment: Cardboard Tube
Method: Using a cardboard tube (or rolled up piece of paper)
look through the tube with your right eye and hold your left
hand up next to the paper with the palm towards you.
Expected Result: You should see that there seems to be a hole
through the middle of your palm.
Explanation: Your right eye see inside the tube and your left
eye sees your open hand. The brain is confused because it
receives such different signals from each eye. So it combines
the images and you appear to see a hole in your hand.
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| Touch the Dot |
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Equipment: Pencil, paper.
Method: Draw a dot on a piece of paper and put the paper about
75 cm in front of you on a table. Sit at the table put a hand
in front of one eye and use your other hand to try and touch
the dot with a pencil.
Expected Result: You will find it quite difficult to touch
the dot accurately at the first attempt.
Explanation: You cannot judge distances easily with only one
eye. You use both eyes to find the exact position of things.
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| Rainbow Colours |
Darren Dowling
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| Sunlight or the light from an
electric light bulb appears colourless and is called white
light. But it is really made up of a mixture of different
colours. We can only see these colours when light passes through
a transparent substance (such as water or glass), which separates
the colours into a rainbow pattern called a spectrum. A spectrum
consists of seven colours - red, orange, yellow, green, blue,
indigo and violet - as well as two other kinds of light (ultra-
violet and infra-red), which we cannot see. You can see a spectrum
in bubbles of water or in a rainbow. |
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| Make a Rainbow |
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Equipment: Mirror, bowl of water,
white paper.
Method:On a sunny day, fill a bowl
with water and rest a flat mirror against the inside. Stand
the bowl so the Sunlight falls onto the mirror. Hold a sheet
of white card in front of the mirror and move it around until
a rainbow of colours appears on it You may have to adjust
the position of the mirror to get this just right. Once the
mirror and card are in the correct position you can keep the
mirror still with a little modelling clay.
Expected Result: The wedge
of water between the mirror and the surface of the water acts
as a prism and splits up the light so you can see the different
colours. This happens because each of the colours in white
light travels at a slightly different speed and is bent (refracted)
inside the prism by a different amount. Violet light bends
the most and red light bends the least
Explanation: If you put a magnify
glass between the mirror and the card you should find that
the lens bends the light so the colours come back together
again and the rainbow disappears. This shows that the seven
colours of the rainbow combine to make white light.
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Colour Spinners
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Equipment: Card, pencil.
Method: Cut out a disc with a diameter
of 10cm. Divide it into seven equal sections. Make each section
about 51° wide. Colour each section with one of the colours
of the spectrum. Make a small hole in the middle of the disc
and push the sharp pencil through. Spin the disc quickly,
what do you see?
Expected Result: You should see the
colours disappear to make a white disc.
Explanation: When the circle spins
quickly, your eyes cannot see each colour separately. You
see only the result of mixing the different coloured light
together. This is why the disc appears greyish white even
though there are really seven colours on it.
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| Fool your Eyes |
Darren Dowling
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| Here are some tricks to fool
your eyes so that objects appear to move when they are really
still and you see objects that are not really there at all!
You can also find out how a confusing background changes the
shape of size of an object. (Optical illusion book)
If your eyes see two pictures very quickly, one after the
other, they may not be able to tell that the picture has changed
and the image will appear to move. You can only register 12
pictures a second as separate images. If the pictures appear
more quickly than this, you see them as moving pictures. Films
that you see at the cinema have 24 photographs (frames) every
second.
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| Make Your Own Movie |
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Equipment: Paper, pencil, small notebook.
Method: Using a notebook with small
pages (or pages put together), on each page of the book draw
one of the pictures in the sequence. It can be anything as
long as each image is only slightly different from the one
before. Make sure you draw on only one side of the page. When
the book is complete flick the pages with your thumb.
Expected Result: You will see your
story come to life.
Explanation: The pages are moving
too fast for the eye to see them as separate images, so it
makes them into a movie.
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