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8353594
P7 1
Description
GCSE Physics Mind Map on P7 1, created by Fin Carson on 30/03/2017.
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physics
gcse
Mind Map by
Fin Carson
, updated more than 1 year ago
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Created by
Fin Carson
over 7 years ago
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Resource summary
P7 1
Naked eye astronomy
Sun appears to travel from east to south in 24 hours
Earth rotation is anticlockwise
Motion of the moon
Moon appears to travel east-west across the sky once in about 25 hours
Moon does a complete orbit of earth in 28 days
Waxing moon = Getting bigger
Waning moon = Getting smaller
Crescent moon = Less than half of moon visible
Gibbous = More than half of moon visible
Motion of the stars
Stars appear to move east to west - due to rotation of earth
The pole stars dont appear to move - all the other stars seem to orbit around the pole stars
Stars appear to travel across the sky once every 23hrs 56min
Sidereal day - 23hrs 56min - strict 360 degree rotation of earth
Solar day - 24hrs - Looking from the sun - Takes a bit more than 360 degrees as the earth is rotating around the sun
Changing night sky
Over months the 4 minutes add up and the stars appear to be in different places
You can only see stars in opposite direction from the sun
Stars that are behind the sun are not visible because it will be daytime when we see it
So at different times of year you can see different stars
Motion of the planets
They appear to move a little bit forwards
Sometimes they are known to slow down and reverse direction known as retrograde motion
This is because the earth overtakes mars on orbit and therefore we see mars in different places
Celestial sphere
Declination is measuring up from the equator
Ascension is across the equator
Anything we see in the sky we can give it an angle by imagining that all the stars rest on a bigger sphere outside the earth
Eclipses
Solar eclipses
Not that frequent because of factors:
Tilt of the moons orbit
Only seen in a small part of the earth
The distance from the earth and moon changes - elliptical orbit
Sometimes shadow isnt big enough to be full eclipse
Lunar eclipse
When the moons light gets blocked by earth
Only happens when things line up
Telescopes
Refraction
The speed of any wave is affected by the material that it is travelling though
If a wave is travelling from one medium to another then this can cause the speed to change
A change in speed will cause a change in wavelength (frequency wont be affected)
Wave speed = frequency x wavelength
REVISE HOW TO DRAW LENSE DIAGRAM IN BOOK
As seen from diagram the image will be upside down
Power of a Lense
How strong a lens is (how quickly it can bring parallel rays of light together to a focus) can be measured by its powe
Power (D) = 1/focal length (m)
Power is measured in dioptrees (D)
They are inversely proportional
The longer the focus length the less powerful it is
Two lenses in a telescope
Objective lens - collects light and produces an image
Eyepiece lens magnifies the image for viewing
Eyepiece lens has to gave a higher power than objective
The two lenses need to be the correct distance apart
Magnification of a telescope
It is the size of the angle that something takes up in our view
Another way of describing the size of something is by its angular distance
With 50x magnification the angular size is 50 times bigger
magnification = focal length of objective lens / focal length of eyepiece lens
If the eyepiece focal length is longer then the image will be smaller
A telescope can not make a distant star look bigger as it will still be a blop of light (bad quality)
But a telescope is capable of spreading out stars we thought were one huge star
A good telescope will produce a magnifies image but also bright clear and sharp
The bigger the aperture (end of the telescope) the more light that can come in. So images will be brighter and sharper
Diffraction
When a wave passes through a gap (an aperture)
Small aperture more diffraction
Big aperture less diffraction
To minimize diffraction the aperture has to be larger than the wavelength of light
Because different colours have slightly different wavelengths, we get focuses for different colours - this is called dispersion
Because of this we use mirrors in telescopes as they dont refract
The mirror used in a reflecting telescope must be concave
When parallel rays of light hit a concave mirror they are reflected to a focus in the front of the mirror
Using mirrors gives no problem with dispersion as every ray of light will be reflected by the same focus
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