Light

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What is a luminous source and what are some examples?
Luminous sources give out their own light eg. light bublbs, fire
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What is a non-luminous source and what are some examples?
Non-luminous sources do not gove out their own light eg. moon
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What is it called when the moon casts a shadow on the earth?
Eclipse
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What are the three things that can happen to light when it hits something
pass through-be transmitted, bounce back-be reflected, stay inside the object-be absorbed
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How are shadows formed?
Shadows are formed because light travels in straight lines and cannot pass through opaque objects. Light is blocked by the object and the object casts a shadow.
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Shadows have a very dark centre. What is this part called?
Umbra
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Shadows sometimes have a not so dark outer edge. What is this part called?
Penumbra
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What type of light source produces an umbra?
A small light source
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What type of light source produces an umbra and penumbra?
A large light source
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What happens when light hits an opaque object?
Opaque objects do not allow light to pass through- they absorb, scatter or reflect it
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What happens when light hits a translucent object?
Translucent objects transmit the light but diffuse (scatter) the light as it passes through
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What happens when light hits a transparent object?
Transparent objects transmit the light
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Is the image in a plane mirror real or virtual?
Virtual
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What effect does the mirror have an the image?
It becomes laterally inverted
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What does laterally inverted mean?
The image is reversed: left becomes right and right becomes left
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What angle is the angle of incidence equal to?
Angle of reflection
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What is the angle of reflection?
the ray of light which bounces off the mirror
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What is the angle of incidence?
a ray of light which hits the mirror at a particular angle
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What happens when light hits a smooth surface?
It provides a regular reflection so you can see a clear image of the object
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What happens when light hits a rough surface?
It provides a diffuse reflection and it reflects off in all different directions so you don't see a clear image
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How does light travel?
Light travels in straight lines
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Is light a wave or a particle?
Wave
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What happens when light enters a substance of different density?
It is refracted (changes direction)
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If the substance is more dense how does this effect the light ray?
The more dense the substance is, the more the light ray will change the direction
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What does it tell us about the incident and emergent rays if the block is parallel sided?
The incident and emergent rays are also parallel
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Where does total internal reflection occur?
In dense substances like glass
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What is total internal reflection?
Sometimes light rays never leave the denser substance. They are reflected backwards and forwards inside it. This is called total internal refraction.
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What uses total internal reflection?
Optical fibres
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What are optical fibres?
They are very thin flexible glass rods. Light reflects internally along their whole length.
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What are optical fibres used for?
Bundles of optical fibres, called an endoscope are used to see inside the body. They are also used for data communications, to inspect jet engines and for decorative optical fibre lamps.
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How does total internal reflection occur?
When a light ray travels into a less dense substance, its angle of refracrion is always greater than the angle of incidence
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What happens if the angle of incidence is bigger than the critical angle?
All the light is reflected back into the glass (total internal reflection)
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What happends if the angle of incidence is smaller than the critical angle?
The light is refracted
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What happens to the angle of refraction if the angle of incidence increases?
It also increases
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What is the angle of incidence called if the angle of refraction reaches 90 degrees?
Critical angle
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How does the light stay inside the object in total internal reflection?
The lights stays in because the glass object has a higher density than the air. Also when the angle of light is bigger than the critical angle, the light does not escape.
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Why does a pencil look bent in water?
The ray has been refracted at the edge of the water
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Does light travel slower in glass or air and why?
Light travels more slowly in glass than air because glass is more dense than air.
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What happens if the angle of incidence is zero?
The ray of light passes straight through the glass block and does not change direction.
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What can a prism do to white light?
It can break it up into 7 colours
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What is the order of the colours?
Red, Orange, Yellow, Green, Blue, Indigo, Violet
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What can the colours be combined to form?
White light
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What is different about each colour?
They each have a different wavelength- the length of one wave
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Why does light spilt up?
The light slows down when it enters the glass prism. It disperses because all the colours that make up white light slow down by different amounts.
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Which colour spreads out the most?
Violet
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Which colour spreads out the least?
Red
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When do you see a rainbow?
When you are facing falling rain but with the sun behind you
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How do you see a rainbow?
White light enters a raindrop and is spilt into colours. The raindrop acts as a prism and the light reflects into your eye and you see a rainbow
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Why does an apple look red?
Because the skin of the apple contains a pigment that reflects red light but absorbs all the other colours of the spectrum shining on it
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How do we see white objects?
White objects reflect nearly all the light energy shining on them
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How do we see black objects?
Black objects absorb nearly all the light energy shining on them
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How do wee see coloured objects in general?
Coloured objects reflect light of their own colour and absorb the rest
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What are the three primary colours of light?
Red, blue, green
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What are the three secondary colours of light?
Magenta, cyan and yellow
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What happens when light enters our eye?
It is refracted by the lens and cornea
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Where is the image formed in the eye?
Retina
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What is the retina?
A screen at the back of the eye
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What does the retina contain?
Light sensitve cells called rods and cones
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Where are rods found and what light are they sensitive to?
Around the egde of the retina- sensitive to dim light
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Where are cones found and what light are they sensitive to?
The center of the retina-sensitive to bright light and colour
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How are messages sent to the brain?
Optic nerve
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Card 2

Front

What is a non-luminous source and what are some examples?

Back

Non-luminous sources do not gove out their own light eg. moon

Card 3

Front

What is it called when the moon casts a shadow on the earth?

Back

Preview of the front of card 3

Card 4

Front

What are the three things that can happen to light when it hits something

Back

Preview of the front of card 4

Card 5

Front

How are shadows formed?

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