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6F How We See Things Section 1: Introduction 6F1
Reflective or luminous? Section 2: How light travels
6F2
Light travels in straight lines Section 3: How we see light
6F3
Watch your pupils!
6F4
Diffusion of light Section 4: Exploring mirrors
6F5
Investigating mirrors
6F6
Make a beam of light move around the classroom Section 5: Beams of light
6F7
How to make a beam of light
6F8
Make a magic lantern
6F9
Coloured beams from a CD ROM Section 6: Reflection from surfaces
6F10 How to make coloured filter paper 6F11
Reflecting colours
6F12 Why are things coloured? 6F13 Investigating the colours in light 6F14 Reflecting from shiny and diffusing surfaces 6F15 Reflecting light from a yoghurt carton 6F16 Spinning top Section 7: Shadows and reflections 6F17 Investigating shadows 6F18 Make a mini silhouette theatre 6F19 Build a viewing screen 6F20 Improving light patterns using tracing paper A few tricks of the light 6F21 How to make a pin hole camera 6F22 Viewing a pinhole camera image 6F23 Project an image of your classroom window 6F24 Make the spot disappear 6F25 Put the bird in the cage 6F26 A pencil trick 6F27 Make a coin disappear
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6F Equipment list Specialised equipment Magnifying glass or lens Selection of colour filters Spatula
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Recyclable Cereal packets Jam jar Kitchen towel roll Old CD ROM Shoebox Yoghurt carton
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Standard equipment/ household Black card Card Coin Materials: differing reflectivity Collection of mirrors Coloured transparent paper Crayons Cutter Elastic bands x2 Glue Green object (leaf) IWB Kebab sticks Marker pen Metal Ruler Nail OHP Painting equipment Paper Pencil Plasticene Plywood or MDF Printer Red/Green transparent paper Red object (apple) Rubber band Ruler Scissors Sticky tack Torch Tracing paper Watch White card
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6F1 Reflective or luminous? Print and photocopy worksheet
IWB
Look at the photos above and decide whether the objects are luminous or reflective?
Object
Luminous
Reflects
The moon Bedside lamp Aluminium foil Candle flame The Sun Fire coals A mirror Blue glass
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6F2 Light travels in straight lines Card
Torch
1
Position a piece of card some distance in front of a torch and observe the shadow cast by the card on the table.
2
Sketch the edge of the shadow produced by the card below.
Sketch the shadow produced by the edge of the card below:
If light didn’t travel in straight lines how would the shadow of the card appear?………………………… …………………………………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………………………………
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6F3 Watch your pupils! Pupils in pairs
. 1.Students are to work in pairs. Each student is to observe his/her partner’s eye pupils. 2.Then turn off the lights and tell them to keep looking at each other until they get accustomed to the dark (about 20-30 seconds). 3. Turn the lights back on again. 4. Get them to notice the difference in pupil size.
Draw the pupil diameters in the situations described below:
Cornea
Cornea
Draw your pupil before the lights are turned off.
Draw your pupil after dark accomodation.
Explain why the pupil size changes:… ……………………………………………………………………………………… ……………… …………………………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………………………… The pupil size is controlled by the iris. Label the iris and the pupil in the diagram of the eye below:
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6F4 Diffusion of light Torch
Bedroom or darkened classroom
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1
Turn your bedroom light off at night and point a torch into a corner of your bedroom. Observe how the light spreads around the room.
2
Find out from which corners the light spreads out most and least.
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6F5 Investigating mirrors Collection of mirrors
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Card
Sticky tack
Marker pen
1
Draw the image of the sign in the box below.
2
Draw the image of the sign in the box below.
3
Observe the image as you move your head around - what do you notice about it.
Using the rules of reflection ray trace the rays opposite as they reflect off the surfaces.
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6F6 Make a beam of light move around the classroom Watch
Sunny day
1
Get children to use a mirror or a flat watch face to direct a reflection of the Sun around the classroom.
2
Play a game: name an object in the class and see who can direct their reflection on to the object first.
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6F7 How to make a beam of light Black card
Scissors
Torch
Viewing screen (see expt 6F19)
1 2
Cut a 2mm wide strip in a piece of black card.
Place the slit in front of the torch to produce a narrow beam of light.
Make a beam of light
3
Move a viewing screen backwards and forwards in front of the torch and observe what happens to the size of the beam.
Sketch in the diagram below the beam of light as it moves away from the light source:
Black card wih slit
Viewing screen
What happens to the beam if you make the slit narrower. Try it!…………………………………………………… …………………………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………………………… What is ALWAYS TRUE about a beam of light as it moves away from a light source? ……………… ……………………………………………………………………………………………………………………………………………………………………………
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6F8 Make a magic lantern Kitchen towel roll
Scissors
Coloured transparent paper
Rubber band
Small torch
Flatten a long cardboard roll. The type used for kitchen cleaning towels is best.
1
3
2
3
4
Cut geometrical shapes out at the edge as indicated opposite.
Hold a piece of coloured transparency paper over the end of a torch using an elastic band.
Make your magic lantern by holding the torch under the kitchen towel roll as indicated opposite.
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6F9 Coloured beams from a CD ROM Old CD ROM
Rubber band
1
Small torch
Illuminate a the recording face of a CD with a torch and observe the colours reflected on the classroom wall.
2
Alternatively position the CD in sunlight and observe the reflected light patterns.
Draw the colours that you see reflected from the CD ROM in the table below:
Name:
Red
Y
G
Colour in
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6F10 How to make coloured filter paper Printer
Template provided
1
Print the filter “master” on the following page on special transparency paper made for your ink jet printer.
2
Cut a circular hole in a piece of stiff card of about 6 cm diameter.
3
Cut the filter from the transparency and stick it to the cardboard.
!
4
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Use a well ventilated area for gluing.
Finally trim the edge of the filter.
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6F10 How to make coloured filter paper
C, M, Y : 0 ,100, 0
C, M, Y : 100 , 0, 0
C, M, Y : 100 , 0, 0
C, M, Y : 0 ,100, 0
C, M, Y : 0 , 0, 100
C, M, Y : 0 , 0, 100
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6F11 Reflecting colours OHP or white paper
Selection of filters (see expt 6F10)
Examine various combinations of primary filters on the overhead projector. Alternatively place on top of white paper.
Find which colours are transmitted by the following filter combinations. Colour in the overlap.
Colour transmitted:
Mag
Yel
Mag
Cyan
Cyan
Yel
…………………
…………………
…………………
Mag Cyan
Colour transmitted:
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Yel
……………………………
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6F12 Why are things coloured? Scissors
Red and Green transparent paper
Rubber band
Torch
Green object (leaf)
Red object (apple)
Red transparent paper
1
Position a green leaf behind a sheet of red transparent paper and note its colour.
2
Now position a red object behind a sheet of green transparent paper and note its colour.
Green transparent paper
What colours do the leaf and apple appear when viewed through the filter papers shown above? a) apple (through a green filter): ………………………… b) leaf (through a red filter): ………………………… Why does this happen? ……………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………………………………
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6F13 Investigating the colours in light Jam jar
White card
1
2
Fill jam a jam jarjar right right up to up thethe to brim brim withwith water water and position position ititon onthe the edge of of the a table tableclose to a window.
Position some white paper on the floor to observe the colour spectrum produced by the jam jar.
Light is made of different colours. When these colours pass through a prism (or jam jar filled with water) some colours get bent (refracted) more than others. Colour in the visible spectrum that appears on the white paper in the diagram below. Indicate which colour is bent (refracted) most and which least: Most refracted
Least refracted
Investigate what happens when you place various pieces of coloured transparency in front of the jam jar.
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6F14 Reflecting from shiny and diffusing surfaces Collection of materials to test reflective properties (see below)
Torch
1
Write a word or draw a symbol of similar size on different surfaces (see table below)
2
Illuminate each surface with a torch as idicated below and note the quality of the reflected image on a piece of white paper.
Marker pen
Collection of household
Sample reflecting surface
White paper
For each surface, observe the quality of the reflected image ( that is, has the information been preserved or has it been disordered?) Surface
Was the reflected image visible?
Mirror Paper Aluminium foil Plastic
Both white walls and mirrors reflect equal amount of light however you cannot see yourself in a white wall. How is the surface of a white wall different to that of a mirror? ……………………………………………………………………………………………………………………………………………………………………………
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6F15 Reflecting light from a yoghurt carton Yoghurt carton
Plasticene or coloured tissue paper/card
Torch
1
Cut circles from various coloured serviettes or tissue papers.
2
Place the circle into the bottom of a white yogurt carton (with the label removed).
3
Shine a torch into the yogurt carton and note the colours of its walls.
What colour is the light when it leaves the torch? ……………………………………………………………………………… What colour is reflected from the tissue paper? ………………………………………………………………………………… When you shine light into the yoghurt carton what colour do its walls glow? ………………………………… Can you explain why? …………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………………………………
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6F16 Spinning top Scissors
Cereal packets
Pencil
Sticky tack
Painting equipment
1
Paint a cardboard disc in equal segments with the three primary colours as indicated below:
2
Push a small pencil through the centre of the disc and hold with blue tack.
3
Now spin the top you have made and note what happens to the colour as you spin it.
What colour does the spinning disc appear for the following combinations of paints or inks? Combination
Magenta-cyan
Cyan-yellow
Yellow-magenta
Yellow-magenta-cyan
Apparent colour
Why does this happen?………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………………………………
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6F17 Investigating shadows Torch
Viewing screen (see expt 6F19) Various objects
1
2
Illuminate an object placed in front of your viewing screen (see expt 6F19) and observe the shadow.
Move the viewing screen backwards and forwards and note below what happens to the size and clearness of the shadow.
What happens to the size of the shadow as you move the screen away from the object?………… …………………………………………………………………………………………………………………………………………………………………………… What happens to the size of the shadow as you move the screen towards the object?……………… …………………………………………………………………………………………………………………………………………………………………………… Ray trace the rays through to the viewing screen to show the size of the shadow in the diagram below:
Viewing screen
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6F18 Make a mini silhouette theatre Black card
Viewing screen
Kebab sticks
Scissors
Torch
Think of a simple story with a few characters. Little Red Riding Hood for example.
1 2
Cut out silhouettes of the characters in the story.
3
Stick the characters to cock tail sticks wooden tooth picks using wood glue.
Now act out the play by illuminating the viewing screen made in expt
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6F19 Build a viewing screen Cutter
Pencil
Metal Ruler
Spatula
Plywood or MDF (3 x 150 x 100 mm)
Teacher or Technician only.
Wooden support
Glue
Tracing paper
Draw and cut out a rectangular frame from a piece of 3mm MDF or stiff cardboard such as a shoe box. Drill small holes just inside each corner to assist in cutting process. 100mm
150 mm !
Metal ruler
Use a rough working surface.
2 !
Glue the frame to a wooden base using wood glue.
Use a well ventilated area for gluing.
3
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Cut with a sharp knife on a rough surface. Press lightly using a metal ruler as a guide and repeat until complete.
Cut out a piece of tracing paper and stick to the frame as shown opposite.
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6F20 Improving light patterns using tracing paper Torch
Tracing paper or viewing screen (see expt 6F19)
1
Darken the room as well as possible.
2
3
Illuminate the wall with a torch light and take note of the pattern of light produced on the wall.
Repeat with the diffusing screen infront of the torch.
Compare the illumination produced by the torch with and without the diffusing screen?…………… …………………………………………………………………………………………………………………………………………………………………………… Illuminate a “spiky” object such as a hair brush or pin cushion using a torch with and without a diffuser. Compare the shadows in each case. …………………………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………………………… Illuminate your face using a torch with and without a diffuser. How do the shadows compare in each case? ………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………
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6F21 How to make a pin hole camera Cutter
Scissors
1
Metal Ruler
Shoebox
Glue
Tracing paper
Nail
Elastic band
Draw and cut out a rectangular window on the back of a shoe box.
2
Stick tracing paper over the window using glue or sellotape.
!
3
Make a 1mm to 1.5 mm hole in the centre of the shoe box lid with a small nail.
4
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Use a well ventilated area for gluing.
Tightly secure the lid to the box using a couple of large elastic bands.
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6F22 Viewing a pinhole camera image Shoebox camera viewer (see previous expt)
1
Turn off the light and pull blinds down except for one window which will act as an illuminated object.
2
Position the shoe box camera (expt 6F21) some distance away from the window and observe the image.
Window acts as infinity object.
Ray trace the rays through from the object to the image plane: How is the image orientated w.r.t the object? ………………………………………………………………………
Is the image bright or faint? ………………
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6F23 Project an image of your classroom window Magnifying glass or lens
1
Viewing screen
Turn off the light and pull the blinds down except for one window which will act as an illuminated object.
2
Move the lens towards and away from the screen until you see the image of the window.
Window acts as infinity object.
How is the image orientated with respect to the object?…………………………………………………………………… Lenses are used to form images. They collect light that comes from one point on an object then bend the light to the same point on an image. Using the diagram below, trace the rays from the top and bottom point of the object through to the corresponding point in the image:
Object
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Image Lens
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6F24 Make the spot disappear Paper
Ruler
Marker pen
1.Draw two 3mm diameter black spots about 70 mm apart on a piece of card. 2.Hold them in front of your eyes.
70mm
3.Close the left eye. Watch the left spot with the right eye (but paying attention to the right spot). 4.Move the paper backwards and forwards until the right spot disappears.
Indicate the following on the diagram opposite: a) The retina. b) The optic nerve. c) The blind spot.
What is the function of the retina? ………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………………………… What causes the blind spot?……………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………………………… In this experiment what causes the spot to disappear?……………………………………………………………………… …………………………………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………………………………
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6F25 Put the bird in the cage Card
Crayons
1
Elastic bands x2
Draw two diagrams on separate cards as indicated below, stick them together and make holes with a hole punch at the top and bottom.
2
Attach two elastic bands at either end. Wind up the card then release it.
Why does the bird appear to be inside the cage as the card spins?………………………………………………… …………………………………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………………………………
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6F26 A pencil trick Beaker 250 ml or jam jar
Pencil
A
Move the eye from positions C to A and observe what happens to the pencil tip.
B
C
Virtual image Object
What did you observe happen to the pencil tip as you moved your eye from C to A?…………………… …………………………………………………………………………………………………………………………………………………………………………… What type of image is formed in this experiment, virtual or real?…………………………………………………… Explain your answer:……………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………………………… The effect is caused because the rays leaving the pencil tip are refracted (bent) when they pass from water to air. Try to explain the effect by: a) ray tracing the paths towards the eye pupil. b) reconstructing what the brain sees.
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6F27 Make a coin disappear Beaker 250 ml or jam jar
1
Coin
Place a jam jar of water on top of a coin as indicated opposite.
A
2
Move your eye from A to B and watch what happens to the coin. B Coin
What happened to the coin as you move your eye from A to B?………………………………………………………… …………………………………………………………………………………………………………………………………………………………………………… When your eye is at a high position you can see the coin because light passes through the bottom of the jar to the coin and reflects off of it (figure 1). However, as your eye position lowers there is a particular angle when the light is no longer able to reach the coin. Instead, it totally reflects from the glass-water surface (figure 2) and never reaches the coin. So the coin becomes invisible. This phenomenon is called total internal reflection.
Figure 1
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Figure 2
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