# lenses

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## reflection and refraction

When a wave hits a boundary between one medium and another some of it is reflected. angle of reflection is the same as anfle of incidence reflection happens when there is a change in densities. Refraction waves travel at different speeds in different densities when a light ray passes from air to glass the ray slows down and is bend towards the normal. when a light ray passes from glass to air it speeds up and bends away from the normal

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## virtual and real images

Real image when light from an object comes together to for an image on a screen.

Virtual image  when light rays diverge so light from object looks like it has come from a different place.

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## converging lense

A coverging lens is convex (bulges outwards) parallel rays of light converge to a focus

axis: line passing through middle of lens

focal point: where rays come together each lens has a focal point in front and behind

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## Drawing a ray diagram for a converging lens

draw ray from top of object to lens parallel to axis of lens

draw ray from top of object passing through middle of lens

draw refracted ray passing through fcoal point

mark where rays meet

reapeat for a point on bottom of object

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## focal length

distance from lens to focal point

clamp lens at one end of track and white card at other end

set up near a window focused on a distant object

move card until image is focused measure distance from lens to image

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## distance from lens affects image

clamp lens at one end of track and white card at other end with object on other side of lens to card move object until image is focused measure distance from object to lens.

OBJECT AT 2F: REAL UPSIDE DOWN IMAGE SAME SIZE AS OBJECT AND AT 2F

OBJECT BETWEEN F AND 2F : REAL UPSIDE DOWN IMAGE BIGGER THAN OBJECT AND BEYOND 2F

OBJECT FURTHER THAN F: VIRTUAL IMAGE RIGHT AY UP BIGGER THAN OBJECT AND ON SAME SIDE AS LENS

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## refracting telescopes

a refracting telescope has an eyepiece lens and objective lens

objective lens coverges rays of light to form a real image at the focal point of objective lens the light from real image enters eyepiece lens which spreads rays out so they leave at a wider angleand fill more of your retrina making image look magnified.

incident ray parallel to axis will pass tgrough focal point when its reflected.

incident ray passing thrrough focal point will be parallel to axis when its reflected.

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## refracting telescopes part two

converging lenses  draw ray from top of object to mirror parallel to axis draw ray from object to mirror passing through focal point. draw reflected ray passing through focal point. draw reflected ray parallel to axis of mirror mark where rays meet.

reflecting telescope collects parallel rays of light from space the larger mirror reflects rays onto a smaller mirror in front of large mirrors focal point . the small mirror reflects rays of light through hole in second mirror a real image is formed behind mirror an objective eyepiece lens is used to magnify image

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