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Converging lens

Any lens that is fatter in the middle than at the edge.
The longer the focal length, the larger the real image will be.

Estimating focal length

Lens with a long focal length are thin ­ its
surfaces are not strongly…

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For example ­ telescope used to see the moon is labelled 50X
Moon appears 50 rimes closer
Moon's angular size seem 50 times as great

Telescopes do not make distant object look any bigger. They spread out a group of stars allowing
them to be seen separately.

Magnification = focal…

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Telescopes with magnification greater than about 6X needs support.
They must be moveable ­ rotation around two axes at right angles to each other enables a
telescope to point in any direction.
Use a tripod to support telescopes
Bearings must have low friction
Weight of the telescopes must be balanced…

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Some telescopes orbit around the Earth. This is to avoid atmospheric pollution and refraction of
light. Also the atmosphere absorbs some electromagnetic radiations such as Xrays, gamma rays
and some infrared.

Twinkling (scintillation) is caused when starlight passes through the atmosphere.
The atmosphere is not uniform. Some areas are…

Page 5

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When the Moon is in the direction of the Sun, the side that is in darkness faces the Earth. NEW
Solar and Sidereal Day

The stars appear to travel across the sky once every 23h 56m. This is 4 minutes less than the time
taken by the Sun. The…

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From months 1 to 3, Mars seems to move forwards, then for 2 months it goes into reverse before
moving forwards again.

Solar eclipse ­ Moon blocks the Sun's light Lunar eclipse ­ Moon moves into the Earth

The Sun moves slightly faster The Moon moves behind the…

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Parallax angles are measured in fraction of a second of arc. There are:
360° in a full circle
1° of arc = 60 minutes
1´ minute of arc = 60 seconds
1 second of arc is 1 of a degree

The smaller the parallax angle, the further away…

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The spectrum is turned into a graph which shows the intensity for each frequency in the spectrum.

Hotter star, the area under the graph is greater ­ luminosity is greater
Hotter star, the peak frequency is greater ­ produces a greater proportion of
radiation of higher temperature


Cepheid variables…

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spectrum. The further away the galaxy, the greater the speed of recession.

Hubble constant

Speed of recession = Hubble constant x distance
The Hubble constant shows how the speed of recession is linked to the distance.
The Hubble constant was accepted as 72+8 km/s Mpc

Big Bang Theory

The Universe…

Page 10

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Photons of energies 2, 7 and 8 would be absorbed and 1,6 and 9.3 would not be absorbed.

Ernest Rutherford realized that alpha and beta particles are smaller than atoms. Hans Geiger and
Ernest Marsden carried the experiment:

Use gold foil and roll it to a thickness…


Ashir Sajid


brilliant notes, just what i was looking for. Thanks

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