# P5h: Optics

Projecting an image onto a screen is a large industry and involves big money; especially if it’s you they are projecting. The cameras used to film the movies use a complex arrangement of lenses to zoom in and focus on the actors, and the images they form are real but inverted.

On a more modest theme many people would struggle with day-to-day life or be unable to read clearly without spectacles. This item takes a look at the many uses of optical devices.

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What four things are convex lens used in?
Some spectacles, magnifying glasses, projectors and cameras.
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What do convex lenses produce?
Real images on a screen.
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What lengths do thin and fat lenses have?
Thin have long focal lengths, and fat have short focal lengths.
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Describe the focal length of a convex lens.
The focal length of a convex lens are measured from the centre of the lens to focal point.
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Whats another name for a convex lens?
Converging lenses.
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Describe what happens to light incident on a convex lens parallel to the axis.
It is refracted through the focal point.
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Describe the shape of a convex lens.
It bulges outwards.
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Describe the effect of a convex lens on a diverging beam of light
They convert it into a parallel beam of light.
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Describe the effect of a convex lens on a parallel beam of light
They convert it into a diverging beam of light.
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What's the principal axis?
The principal axis is an imaginary line at 90° to the face of the lens, and passes through its optical centre.
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What's the focal length?
The distance from the centre of the lens to the focal point.
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What's the focal point?
Light rays passing through the lens parallel to the principal axis are focused to a single point.
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What is the equation for magnification?
image size/object size
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Explain how convex lens are used in camera.
when take photo,light from object travels 2 camera&refracted by lens,formin image on light sensor.this is real image cuz light rays actually meet there.image is smallr than object,cuz objects further away than focal length of lens.image is inverted.
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Explain how convex lens are used in projectors.
in projectors,object is closer than focal length of lens,so image is larger.when u project an image,object needs to be placed upside down&very close to lens.the light from object is refracted by lens&produces a real,inverted,magnified image on screen
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What does inverted mean?
Upside down
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Describe how convex lenses create magnified images.
The object being magnified must be closer to the lens than the focal length. The image produced is a virtual image.
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Explain how the images produced by cameras and projectors are focussed.
an image will be infocus when light that forms it converges on screen/sensor.in cameras&projectors the image is focused by moving lens closer to/further from,the object.the closer to the object the lens is,the further from lens the image is formed
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Explain the refraction by a convex lens
will go parallel.
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Explain the refraction by a convex lens of a ray incident on the centre of the lens.
It doesn't bend.
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What is a real image?
A real image is the image formed where the light rays are focussed.
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What is a virtual image?
A virtual image is one from which the light rays appear to come but don’t actually come from that image like in a mirror.
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Can a virtual image be projected on a screen/film?
no.
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## Other cards in this set

### Card 2

#### Front

What do convex lenses produce?

#### Back

Real images on a screen.

### Card 3

#### Front

What lengths do thin and fat lenses have?

### Card 4

#### Front

Describe the focal length of a convex lens.

### Card 5

#### Front

Whats another name for a convex lens?