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Physics P7 revision notes
Observatories and telescopes
· Stars are so distant that their light is effectively parallel
· Converging (convex) lenses and concave mirrors can be used to focus
parallel rays of light.
o The more curved the lens, the more powerful it is.
!
· Power of lens…

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F




Parabolic reflector

· But if parallel rays comes from another direction, they are focused at a
different point, like this (the blue dot)




F




· The focal point is where you look at the image, So, for a parabolic mirror
telescope to be able to look at different stars,…

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Light from one
side of the galaxy




Light from the other
side of the galaxy




· A telescope with two lenses works like this:
o Parallel rays of light from a distant object enter the objective lens
o The objective lens focuses the parallel rays, producing a larger image
o…

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· A lunar eclipse is when the Earth is between the sun and the moon.
· Different stars are seen in the night sky through a year, as the earth travels
around its orbit.

Galaxies
· The Milky Way Galaxy is a spiral galaxy with a black hole in its…

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· The spectrum of a star has a continuous range of frequencies, plus lines that
indicate chemical elements present.




· A molecular model can be used to explain why the pressure and volume of a
gas vary with temperature.
· Kelvins (K) use the same gauge as centigrade, but start…

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· Stars with a mass 8 times or more than the sun become red supergiants.
These have enough mass to compress the core further, until most of it is iron.
o The outer layers of the star are no longer held up by the pressure of the
core, so collapse…

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§ working conditions for employees
o most optical and infrared telescopes are situated in Chile, Hawaii,
Australia and the Canary Islands
· Some telescopes are put into space to reduce the effects of the atmosphere,
which refracts and absorbs electromagnetic radiation
· Putting telescopes into space has advantages and disadvantages.…

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merci beaucoup 

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