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116 Cards in this Set

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  • Back
When are objects visible?
When light strikes them.
What is light a mixture of?
Light is a mixture of electrical and magnetic energy.
What does the electromagnetic spectrum consist of?
The electromagnetic spectrum includes visible and invisible light.
What is white light a combination of?
White light is a combination of all the colours of the rainbow or the spectrum.
What are the colours of the rainbow?
Red
Orange
Yellow
Green
Blue
Indigo
Violet
What is the speed of light?
186,000 miles per second.
300,000 km per second
How long does it take for light to travel from the sun to earth?
About eight and a half minutes.
How long does it take for light to travel from the nearest star (not the sun) to earth?
4 1/2 light years (Alpha Centauri.)
Everything in the universe is one of two things. What are these?
Matter or Energy
What is energy and what are the two types of energy?
Energy is the ability to move matter. The two kinds are kinetic and potential.
How does light travel
In waves and in streams. They are made up of particles called photons. These particles move energy from one place to another.
How fast does light travel?
186,000 miles per second (300,000 km per second).
What are some of the light waves invisible to humans?
Infrared waves, microwaves, ultraviolet waves, x-rays, gamma rays.

They travel at the same speed but have different wavelengths and frequencies.
What is a wave's wavelength?
The distance between the peak of one wave and the next.
What is a wave's frequency?
The number of waves that pass a specific point every second.
What is the connection between wavelength and frequency?
The longer the wavelength the lower its frequencey and the less energy that it contains.
What happens to light when it moves from one medium to another?
It changes directions which slows it down.
Why can we see light in the sky?
Gas molecules, dust and other particles in the atmosphere reflect the light.
How much of the sun's energy reaches earth as light and heat?
One thousandth of one millionth part.
How much of that energy reaches the earth?,
Almost 30% of that energy is reflected back.
What is the sun mostly made up of?
Hydrogen gas.
How does the sun produce energy?
Atoms of hydrogen heat up and move about at high speeds. They collide with other hydrogen atoms which produces helium. This is called nuclear fusion and it is through this process that electromagnetic energy is released from the Sun.
How far can light travel in one year.
5,870,000,000,000 miles.

(say, six milion, million miles)
Sun is essential to life. What is the process by which plants turn light into energy.
Photosynthesis.
What are living organisms which produce their own light called?
Bioluminescent
Why is sunlight and photosynthesis crucial for all life?
Without this there would be no food for other animals or man.
Other than the sun what are some natural light sources?
Stars, fire, lightning, and rocks (that glow with a light which gives of no heat).
As most matter does not produce its own light what three things must occur if we are to see them?
(1) There must be a source of light (eg sun) (2) Light from the source must strike the object (3) The light must be reflected from the object and then travel to the viewer's eyes.
What type of surface is light best reflected from?
Shiny surfaces, such as mirrors or screens.
In what way is the movement of light like that of a ball?
When a ball strikes a surface at an angle it bounces off in the opposite direction at the same angle. If it hits a surface straight on it bounces straight back. Light is similar.
What is the ray of light hitting a surface called?
It is called 'the incident.'
What is the law of reflection?
'The angle of incidence is equal to the angle of reflection.'
If you look at your reflection in a crumpled piece of aluminium foil why will you see an irregular reflection?
The law of reflection does not hold true for rough surfaces. As the surface is rough each ray is reflected irregularly and so the light spreads out in all directions (is 'diffusely reflected.')
Why are shadows formed?
Light travels in a straight line. When it strikes an object that it cannot go through a shadow is formed.
Matter has varying degrees of density. What is density?
Density is the amount of matter in a substance compared to its volume. (eg. a piece of wood and cake can be the same size but the wood weighs more as it is denser).
Light travels in straight lines. What happens when light strikes an object?
The light rays bend and change direction.
What is different about light rays hitting a mirror to hitting glass or water?
When the light ray hits the mirror it is all reflected back. When it passes from one see-through object to another the light rays bend.
What do we call this bending of light rays?
Refraction.
What decides how much the light refracts?
The direction in which the light refracts depends on the density of the substance that it strikes. If moving from a dense substance to a less dense one the light will speed up; if to a substance of greater density the speed of light is slowed down.
When does light travel at its fastest?
When it travels through a vacuum. it slows down when travelling through air, water or glass.
Does light travel slower in water or in air?
Light travels slower through water than through the air.
How does refraction cause mirages?
The light refracts as it travels through the boundary between the warm air that has been heated and the cooler air. Mirages are most common when it is hot, little wind and a blue sky.
Why does the sky appear blue?
Sunlight is made up of all the colours of the spectrum. As it passes through the atmosphere the blue wavelengths of light are scattered making the sky appear blue.
What happens to light when it passes through a prism?
As the light passes through the prism the angle at which it is travelling is changed. This causes refraction. Different wave lengths travel at different speeds.
How does a prism split white light?
It splits whitelight into a spectrum according to wavelength, energy and frequency. The prism bends different wavelengths to different degrees. Red is bent the least and violet the most.
What carries more energy - the photons in a blue lightwave or the photons in a red lightwave?
Blue photons carry more energy than red photons. The shorter the wavelength, the greater the amount of energy.
What are waves outside of the red-end of the spectrum called?
Infrared waves. They are invisible to us as they do not carry enough energy to stimulate the cones in the human retina.
Do man-made objects emit any infrared light?
Nearly everything in the natural world emits infrared light as do many man made objects such as ovens. This light is the result of molecules vibrating rapidly as they are heated.
What happens if this infrared light is heated?
As thermal energy is added the molecules vibrate more rapidly causing the wavelength to become shorter. The object eventually becomes so hot that it emits light wavelengths short enough to be seen.
When is a shadow formed?
A shadow is formed when light strikes opaque material that it cannot travel through.
What causes a rainbow?
The sun shines immediately after a rainshower. The raindrops act as prisms that bend the sunlight causing the whole spectrum to be visible.
What three primary colours is white light made up of?
Red, blue and green light. All the colours of the rainbow are made from these three lights.
Light is made up of small particles called photons. Describe photons?
Photons are small particles. They carry different amounts of energy. Red light photons carry the least amount of energy; orange light carry a little more. This continues all the way to violet which carries the greatest amount of energy.
Each colour in the rainbow has a different wavelength. Describe wavelength.
Red light has the longest wavelength which means it has the lowest frequency and carries the least amount of energy. Violet light has the shortest wavelength which means it has the highest frequency and carries the greatest amount of energy.
What is the height of a lightwave called?
The height of a lightwave is called the amplitude. The amplitude determines the brightness of the colour. The higher the amplitude of a lightwave, the brighter its colour; the lower the amplitude of a lightwave the duller its colour.
How are we able to see objects?
We see objects because of the light that they reflect. A white shirt appears white as all the colours of white light are reflected to the eye in equal amounts. A black shirt appears black as all the colours of white light are absorbed equally so no single colour is reflected to the eye.
Why does a red apple look red or a tree look green?
A red apple looks red as it reflects only the red wavelengths of white light. A tree looks green because its leaves reflect the green wavelengths of white light.
What are pigments?
Pigments are powdered substances that can be used to make colour materials. They can be found naturally or made by man.
How are the primary colours of paint different to light?
The primary colours of paint are different from those of light. The primary colours of paint are red, yellow, and blue.
What are the combinations that can make different colours with paint?
Red + Yellow = Orange
Yellow + Blue = Green
Blue + Red = purple
Red + Blue + Yellow = Gray/Black
Why does the sky appear blue during the day?
During the day the sky appears to be blue as the short light waves of sunlight are easily scattered by the gas and dust molecules in the air.
Why does the sky look black in space?
Because there are few gas and dust molecules. In the emptiness of space light travels in a straight line and is seldom scattered.
Why is the light different colours at sunrise and sunset?
At sunrise and sunset the rays are at a greater angle to reach the Earth. They also pass through more dust and air particles than it would at noon. This causes the shorter wave lengths to be widely scattered and to be absorbed by moisture in the atmosphere and clouds. This allows the longer red and orange light waves to be seen in the sky.
What type of matter can light waves travel through?
Through matter that is transparent (see-through).
Why can light pass through transparent material?
Transparent material allows most of the light to pass as only a small amount of light is absorbed and reflected.
What does translucent mean?
It permits light to pass through even though it is not transparent. Light is diffused so that objects are not so clearly visible.
Why are lampshades often made out of translucent material?
As light from the bulb hits the lampshade the light is scattered in all directions by the tiny translucent particles in the shade.
Why cannot light pass through opaque material?
Opague materials absorb or reflect all of the light that strikes it.
Do all opaque matters act the same when light strikes them?
No. They differ a lot in terms of how much light they absorb and how much they reflect. (e.g. Think of a door and a mirror).
What objects can cast a shadow?
Only opaque objects or translucent objects that only let a little light through can cast a shadow?
What does the size of the shadow depend upon?
(1) the distance between the light source and the opaque object (2) the surface the shadow falls on.
Describe what happens to a tree's shadow during the day?
In the early morning with the sun in the east the shadow is on the west side of the tree. At midday with the sun overhead the shadow can hardly be seen. In the late afternoon when the sun is in the west the shadow is on the east side.
What was used to tell the time before the inventions of clocks?
Sundials.
What determines the clarity of a shadow?
Its light source. A small, concentrated light source creates a shadow with a clear outline. In contrast, a large extended light source creates a shadow with a fuzzy outline.
What shadow will appear darker - that of an opaque object or that of a translucent object?
The opaque object's shadow will look darker as it does not allow any light to pass through whereas some light is coming through the translucent object.
When does a lunar eclipse occur?
When the earth passes between the sun and the moon. The shadow from the earth is cast onto the moon so that it cannot be seen.
In an eclipse what is the umbra and what is the penumbra?
The umbra is the darkest part of the shadow where no light falls. The penumbra is the fuzzy area on the edge where some light falls
How can an object create more than one shadow?
If there is more than one light source.
How can we see the moon?
The moon does not give off light but we see it when light from the sun reflects from it.
What were the first mirrors made off?
Highly polished material.
How does a mirror work?
It is clear smooth glass. It is silvered on the back so that light reflects from the silver backing rather than passing through it.
What is a lens?
A lens is a curved piece of glass (or other transparent substance) used to focus light rays by bending them.
What is a concave lens?
A lens that is curved inwards is called a concave lens. It is thick at the ends and thin in the middle. When light passes through a concave lens the rays spread apart.
What is a convex lens?
A lens that is curved outward is called a convex lens. It is thin at the ends and thick in the middle. When light passes through a convex lens the rays refract inwards where they meet at the focus of the lens..
Does a convex lens enlarge image or reduce images?
A convex lens enlarges images (magnifies).
Is the lens in the eye convex or concave?
Convex.
What are the parts of the eye called?
The pupil is the small black hole through which the light enters. This is in the middle of the iris. The cornea is a thin clear disc which protects the pupil. The retina is a light sensitive layer at the back of the eyeball.
How does the eye cope with different amounts of light?
If it is dark the cornea causes the pupil to expand to allow more light through. If it is bright it causes the pupil to get smaller so that less light gets through.
Does the lens in the eye change shape.
It becomes thicker when looking at things close up. This causes the light to refract more and so helps to focus on things that are close.
How is the image that the eye produces appear on the back of the retina?
It appears upside down but the human brain automatically turns the image the right side up.
What is a nearsighted person?
A near sighted person can see objects that are near but has difficulty seeing objects far away. Concave lenses are used to correct nearsighted vision.
What is a far sighted person?
A far sighted person can see objects that are far away but has difficulty seeing objects that are near. Convex lenses are used to correct farsighted vision.

End of lesson 11
What is a laser?
A laser is a device that turns an ordinary beam of light into a straight, narrow beam of very bright light.
What is laser an acronym for?
Light
Amplification by
Stimulated
Emission of
Radiation
How is a laser different from ordinary light?
Laser light does not scatter in all directions.

Ordinary light produces many different wavelengths of light whereas laser light contains a very narrow range of wavelengths.

A laser beam is so intense that it can travel long distances without fading.
What are some of the uses of lasers?
Industry - can cut through strong metals.
Shops - reading bar codes
Surveying - a straight, precise beam.
Compact Discs.
Medicine - precise surgery and detecting diseases
Communication - Fibre optic cables.
What do light rays do to the earth's surface when they strike it?
They warm up the earth's surface. Natural light sources produce heat energy.
What is the earth's main source of heat energy?
The Sun.
Describe heat?
Heat is thermal energy. Thermal energy is constantly moving from matter at a higher temperature to matter at a lower temperature.
How is heat energy from the Sun produced?
Heat energy from the Sun is produced through nuclear fusion.
Does the moon produce any heat or light energy?
No. It reflects light from the Sun.
Is heat a form of energy?
Yes. Light and heat are both energy.
What two things must everything in the universe be one of?
Matter or Energy.
What is matter?
Matter is anything that has mass and occupies space.
What is matter made up of?
Small particles called atoms. Two or more atoms linked together are called molecules.
What is heat a byproduct of?
Heat is a byproduct of the movement of atoms and molecules.
What happens when matter is heated?
The atoms and molecules begin to move faster resulting in more kinetic energy. The faster an object's molecules move, the hotter the object gets. The colder an object the slower its molecules move.
What measures temperature more accurately - a thermometer or the sense of touch.
A thermometer.
What is the usual scale used on a thermometer in Europe and in America?
In Europe it is Celsius and in America it is Fahrenheit.
What is the heat of boiling water and the freezing point in these scales?
In Fahrenheit the boiling point of water is 212 F and 32 F. In Celsius it is 100 C and 0C
Do Temperature and Heat refer to the same thing?
No. For instance a candle has a high temperature but little heat and a radiator has a lot of heat but not a high temperature.
What is heat?
Heat is the thermal energy produced by moving molecules.
What are the three ways that heat can travel?
Heat can travel by conduction, convection and radiation.
What is conduction?
Conduction is the movement of thermal energy as heat from one molecule to another by direct contact or collisions.
What is convection?
Convection is the transfer of thermal energy through the movement of hot and cold molecules that carry their energy with them.

This movement produces a circulatory movement.
What is radiation?
Radiation is the transfer of heat through electro-magnetic waves.