Slides in this set

Slide 1

Preview of page 1

OCR GCSE Physics P7
Topic 2 ­ Telescopes and Images…read more

Slide 2

Preview of page 2

Refraction of Waves and Light
· Light changes direction as it passes through one material to another
· This is refraction
· Waves passing through water of a constant depth are equally spaced
· When a waves passes from a deeper section of water to a shallow section
of water the space between the waves gets smaller
· This means that the wavelength gets smaller
· The direction of a wave can also change when they are travelling at an
angle and cross into section of water that is deeper/ smaller
· This happens because the wave hits it at different points
· Wave speed = frequency X wavelength…read more

Slide 3

Preview of page 3

Converging Lenses
· When rays of light enter a converging lens they get refracted
· The refracted light eventually meets at one place (focus) ­ they converge
(hence the name of the lens)
· The distance from the centre of the lens to the focus is called the focal
· The longer the focal length the larger the real image that is produced
· A lens with a short focal length has a large power
· Power (dioptres, D) = 1 (supposed to be over but a bit
focal length difficult to do on a power point)
· A ray diagram shows how a real image is produced through a pin hole
· This is the same principle for a converging lens…read more

Slide 4

Preview of page 4

Optical Telescopes ­ Refracting
· A refracting telescope uses lenses to gather light and focus it
· The bigger the aperture of the lens, the more light and radiation is collected
· This allows us to study very distant objects
· A refracting telescope uses two lenses ­ an eyepiece lens and an objective lens
· The eyepiece lens is the stronger because it needs to magnifies the image for us
· The objective lens is weaker but gathers the light for the eyepiece lens to focus
· Magnification = focal length of objective lens
focal length of eyepiece lens
· Disadvantages of a refracting telescope:
­ They are limited in size because they will sag and bend under their own weight
­ Lenses only focus visible light
­ Some of the light can be absorbed by the lens on the way through if the lens is very
­ Coloured focuses at different points making the image unclear…read more

Slide 5

Preview of page 5

Optical Telescopes ­ Using a
Parabolic Mirror
· A parabolic mirror focuses light at the same point
· Mirrors reflect all rays the same way
· A mirror can be supported so that it doesn't say and bend under its own
· Mirrors can easily be made smooth so that they don't distort the image
· They can be made to focus different types of electromagnetic radiation…read more

Slide 6

Preview of page 6

Dispersion by a Prism or Grating
· When light enters a prism it splits to form a spectrum
· The same thing happens when light passes through grating
· When the light is split to form a spectrum it is called dispersion
· The temperature and chemical composition of the object can be found out
by splitting the light that has been emitted by that particular object
· To find out the temperature and chemical composition you need to use a
spectrometer to show you the spectrum
· The colour of the light depends on the frequency and the wavelength…read more

Slide 7

Preview of page 7
Preview of page 7

Slide 8

Preview of page 8
Preview of page 8

Slide 9

Preview of page 9
Preview of page 9


No comments have yet been made

Similar Physics resources:

See all Physics resources »