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Brain teaser.
• What is at the beginning of eternity, the end of time and space, the beginning of every end, and the end of every place?
What is light?
• Light is also called radiant energy.
• Light is composed of photons, which are small pieces of energy.
The electromagnetic spectrum.
• The EMS is a way of showing all of the different energy waves in the universe.
• They range from very short wavelengths, such as gamma rays (b), to very long wavelengths such as radio waves (a).
Gamma rays
• The shortest wavelength ray, thus it has the highest energy.
• Gamma rays are made when isotopes break down, releasing energy.
• Can be used to kill cancer cells in some people.
X rays
• The next longest wave.
• X rays are also high energy, they can pass through skin and muscle, but are stopped by bone.
• This is why they are used to look at peoples bones!
UV rays.
• Ultra-violet rays are the next longest ray.
• They are made in the Sun and travel to Earth.
• Most are reflected back into space by the ozone layer, but some travel to Earth’s surface.
• They cause sunburn, which is why we should…
Visible light.
• The part of the EMS we can detect.
• It is made of 7 different coloured wavelengths;
• Red, Orange, Yellow, Green, Blue, Indigo & Violet.
• Violet has the shortest ʎ and red the longest ʎ.
IR rays.
• Infra-red rays are longer than visible light, we can’t see IR but some animals can.
• IR is also called ‘heat waves’ and can be detected using a thermal camera (or a speed camera!)
Microwaves.
• Microwaves get water excited! It causes the molecules to vibrate more and more quickly and thus heat up.
• That’s how a microwave oven works; it gets the food to cook itself!
Radio waves.
• Long waves, up to 100km long!
• When received by an antenna, they are converted to sound.
What can we see?
• We can only see a very small part of the EMS, the visible light section (400 - 700λ).
• Some insects can see ultraviolet (UV) light and cats use infrared (IR) to see in the dark.
Luminosity.
• Luminous objects give off their own light; the Sun, lamps etc.
• Non luminous objects bounce light off their surfaces, but don’t make their own light; mirrors, the Moon etc.
• A sundial is a device that measures time by the position of the Sun. In common designs such as the horizontal sundial, the sun casts a shadow from its style (a thin rod or a sharp, straight edge) onto a flat surface marked with lines indicating the hours of the day.
• As the sun moves across the sky, the shadow-edge lines up with different hour-lines on the plate.
Summary; use the words to fill in the gaps.
Distance lamp medium shadow source straight vacuum
• A desk _______ gives out light. • Something that gives out light is called a _______ of
light.• Light travels in _______ lines.• Light does not need a ______ to travel through. • Light from the Sun travels through the _____ of space
to reach us. • A light year is the ______ light travels in one year.• When an object blocks light there is a
_____________.
• A desk lamp gives out light. • Something that gives out light is called a
source of light.• Light travels in straight lines.• Light does not need a medium to travel
through. • Light from the Sun travels through the
vacuum of space to reach us. • A light year is the distance light travels in
one year.• When an object blocks light there is a
shadow.
Reflector or non reflector?
• Why do some surfaces reflect and others not?
• Collect a sample from the tray.
• Set up the light boxes and see what will reflect and what will not.
• What do the reflectors have in common?
• What about the non-reflectors?
Transparent, translucent or opaque?
• Transparent: completely see through.
Glad wrap.
• Translucent: somewhat see through.
Wax paper.
• Opaque: not see through.
Tin foil, you
Law of reflection.
• The angle of incidence is always equal to the angle of reflection
Key
I= incident ray
R= reflected ray
N= normal line
Øi = angle of incidence
Ør = angle of reflection
Drawing ray diagrams
1. Draw the outline of ray box and mirror.2. Draw a dot where the light leaves the ray
box, another dot further along the light ray, and join the two using a ruler.
3. Draw a normal where the light ray hits the mirror surface with a ruler.
4. Put a dot where the light ray leaves the mirror and another further along the ray. Connect the dots with a ruled line.
Activity
• Complete a ray diagram for;
1. Plane mirror (measure angles)
2. Deeply convex mirror
3. Shallow convex mirror
4. Deeply concave mirror
5. Shallow concave mirror
Mirror drawing
• Fold a piece of paper in half and rule a line down the middle.
• Draw a simple picture on one side of the line, place the mirror along the line.
Now..
• Draw the other half of the picture, using the mirror.
• Have a go with the mirror maze as well.
Law of refraction
• When light enters an optically denser medium it slows down and bends towards the normal.
Activity
• Complete a ray diagram for;
1. Oblong block
2. Triangle block
3. Convex lens block
4. Half circle block
How do we see?
• Incoming light must pass through the cornea and pupil.
• The lens then focussing the light on to the retina.
• The retina then sends electrical signals to the brain, telling you what can see.
Make the model eye.
• Make the model eye, glue it into your notes and label the parts.
• Follow the colour code.
• Don’t forget the clear layers.
• Colour the iris in the same colour as your own eye.
The image is upside down!
• The image transferred to your retina is upside down and must be flipped by your brain.
Eye dissection
• Follow me as we complete the eye dissection.
• Remember this came from a living animal, so respect the materials provided for you.
The lens
• The light enters the eye and is focussed on the retina.
• Set your ray box with a convex lens.
• Draw a ray diagram showing the focal point.
Optical illusions.
• Take a look at the optical illusion cards,
• What’s happening?
• Your eye tricks your brain!• http://www.youtube.com/watch?v=SvNjsOl1Ag0
The colour of light.
• Set up a prism inside the rainbow box and observe the light which leaves the prism.
It’s about waves!
• Each colour has a different wave length, when they combine they create white light.
Newton’s colour wheel.
• Make a colour wheel.• 900 Red• 450 Orange• 450 Yellow• 450 Green• 450 Blue• 450 Indigo• 450 Violet
Activity
• Read Pg 65, in Science book Y9.
• Copy the notes about primary colour lights.
• Then answer Q5 on Pg 67.
Filters.
• Through a red filter; red colours look brighter, light colours look pink and all other colours look dark.
• Through a blue filter; blue colours look brighter, light colours look blue and all other colours look black.
• Through a green filter; green colours look brighter, light colours look green and all other colours look black.