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Light & Optics: Making a Telescope
Dr Lisa Jardine-Wright
How do astronomers make discoveries?
Telescopes with lensesConverging Lens
Convergent rays
f
Experiment 1
1. Move the lens until you see a bright dot next to the pin hole that is in focus.
2. Write down the distance of the lens from the pin-hole = the focal length
MirrorLens (15)Pin-holeLamp
About 15cm
Metre Rule
Experiment 1
MirrorLens (15)Pin-holeLamp
Investigating Lenses
Draw ray diagrams to investigate what happens as you move an object to the lens that its focus. And further away than the focus.
lens
Fobject
F image
Experiment 2a
Graph Paper Screen (shows image)
Lens (15)Lamp Cork (object)
More than the focal length of
your lens
Move the screen until you see a
focussed image of the cork
Investigating Lenses
Draw ray diagrams to investigate what happens as you move an object to the lens that its focus. And further away than the focus.
lens
F object
F
image
Experiment 2b
Graph Paper Screen (shows image)
Lens (15)Lamp Cork (object)
Less than the focal length of
your lens
Move the screen can you find a
focussed image of the cork
Experiment 2b
Lens (15)Cork (object)
Less than the focal length of
your lens
Take screen away and move the
lamp to the side.
Lamp Graph Paper Screen (shows image)
Telescope Experiment
Graph Paper Screen (shows image)
Lens (15)Lamp Cork (object)
Lens (30)
10cm
Refracting Telescopes
Lens 1 Lens 2Object
Image 1
Image 2
F1 F1 F2 F2
Refracting Telescopes
Lens 1 Lens 2Object
Image 1
Image 2
F1 F1 F2
Reflecting Telescopes
How do we make a picture?
“Light”
Visible light is just one tiny part of a much bigger range of waves called:
Electromagnetic Spectrum
Electromagnetic Spectrum
Visible Spectrum
Infra-red
Visible
Light is blocked…
in some wavelengths but not others.
How do we “see” things?
Light is blocked…
in some wavelengths but not others.
How do we “see” things?
http://coolcosmos.ipac.caltech.edu/image_galleries/ir_zoo/
The Sun:Visible
The Sun:Radio
The Sun:Microwave
The Sun:Infrared
The Sun:Visible
The Sun:Ultraviolet
The Sun:X-ray
The Sun:Gamma Rays
The Light from an object can tell us ….
• What it looks like - Its SHAPE & COLOUR
• How far away it is – its DISTANCE
• And EVEN!
• What it is made of – its CHEMISTRY
