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Physics Aqa > 3.9.1 Telescopes > Flashcards

3.9.1 Telescopes Flashcards

(88 cards)

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1
Q

What do convex lenses do to incident light?

A

They focus the light

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2
Q

What are convex lenses also know as ?

A

Converging lenses

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3
Q

What do concave lenses do to incident light?

A

They spread out light

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4
Q

What is the principle axis?

A

The line passing through the centre of the lens perpendicular to its surface

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5
Q

What is the principle focus for a convex lens?

A

the point where incident rays of light will converge

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6
Q

What is the principle focus for a concave lens?

A

The point where incident rays of light appear to be coming from

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7
Q

What is the focal length?

A

The distance between the principle focus and the centre of the lens

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8
Q

The shorter the focal length ….

A

the stronger the lens

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9
Q

What is the real image?

A

The image formed when light rays cross after refraction

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10
Q

What is unique about the real image?

A

It can be formed on a screen

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11
Q

What is the virtual image?

A

The image formed on the same side of the lens

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12
Q

With regards to the virtual image, what happens to the light rays?

A

They don’t cross

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13
Q

What can’t be done with the virtual image?

A

It can’t be formed on a screen

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14
Q

What is the lens formula?

A

1/u + 1/v = 1/f

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15
Q

In the lens formula, what is u?

A

Distance of the object from the centre of the lens

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16
Q

In the lens formula, what is v?

A

Distance of the image from the centre of the lens

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17
Q

In the lens formula, what is f?

A

The focal length of the lens

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18
Q

What is the unit for the power of a lens?

A

Dioptres (D)

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19
Q

What is the power of a lens a measure of?

A

A measure of how closely a lens can focus a beam

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20
Q

What is the value of the power of a convex lens?

A

Positive

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21
Q

What is the value of the power of a concave lens?

A

Negative

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22
Q

Regarding a refracting telescope in normal adjustment, which lens collects light?

A

The objective lens

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23
Q

Regarding a refracting telescope in normal adjustment, why does the objective lens collect light?

A

To create a real image of a very distant object

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24
Q

Regarding a refracting telescope in normal adjustment, why does the objective lens have a long focal length?

A

To collect as much light as possible

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25
Regarding a refracting telescope in normal adjustment, what does the eyepiece lens do?
It magnifies the image produced by the objective lens
26
Regarding a refracting telescope in normal adjustment, why is the eyepiece lens useful?
It produces a virtual image at infinity that reduces eyestrain for the observer
27
Normal adjustment for a refracting telescope is the sum of what?
The two focal lengths or fe+fo
28
Regarding a refracting telescope in normal adjustment, principle focus for the two lengths are always where?
In the same place
29
What is the equation for angular magnification? (magnifying power)
α/β (Larger angle over smaller angle)
30
What happens when α and β are both less than 10 degrees?
α/β = fo/fe
31
Regarding a Casegrain reflecting telescope, what is the primary mirror?
A parabolic/concave objective mirror
32
Regarding a Casegrain reflecting telescope, what is the secondary mirror?
A convex mirror
33
Regarding a Casegrain reflecting telescope, where are the principle foci? (2)
After the secondary mirror and there is a virtual one behind the mirror
34
Regarding a Casegrain reflecting telescope, what lens is used to focus light?
A convex lens
35
What is a merit of reflecting mirrors? (2)
They are very thin They have a coating of aluminium or silver atoms
36
What is an advantage of mirrors having a coating of aluminium or silver atoms?
They are smooth, minimising distortion
37
What do reflecting telescopes prevent? (2)
Chromatic aberation Spherical aberation
38
What is chromatic aberation?
when red light has a greater focal length than blue light
39
In chromatic aberation, why does red light have a greater focal length than blue light?
because blue light is refracted more
40
How can you tell if an image is being effected by chromatic aberation?
the images are produced with coloured fringing
41
What is spherical aberation?
when rays of light are focused in different positions
42
How does spherical aberation occur?
The curvature of the lens or mirror can cause rays of light at the edge to be focused in different positions
43
What types of lenses does spherical aberation effect?
Lenses with large diameters
44
How can you tell if an image has been effected by spherical aberation?
The image will be blurred or distorted
45
How can spherical aberation be completely avoided?
By using parabolic objective mirrors
46
Which is lighter a lens or a mirror?
A mirror
47
What are disadvantages of refracting mirrors?
Glass must not have defects Large lenses can bend or distort under their own weight They're heavy They're not easy to move Large magnifications require large lenses Can only be supported from the edges
48
What is an advantage of using reflecting telescopes?
Eliminates chromatic or spherical aberation They're thin They're not heavy Large ones can be made of smaller ones They can be supported from behind
49
What are similarities of radio and reflecting telescopes?
They focus incoming radiation and focus it They can be moved to focus on different objects They both have a parabolic shape
50
What are differences between radio and optical telescopes?
Radio telescopes have a very large diameter, to collect radio waves (due to their large wavelength) Radio telescopes are much cheaper to build Radio telescopes have to move to focus on objects Radio experiences a large amount of man-made interference Radio has a better collecting power Radio must have a much greater diameter to achieve the same resolving power as optical telescopes
51
What are infrared telescopes made up of?
Large concave mirrors focussing radiation onto a detector
52
How must infrared telescopes be kept? (2)
Cooled using cryogenic fluids to almost absolute 0 Shielded to prevent thermal contamination
53
What areas of space do infrared telescopes observe?
Cooler regions of space
54
Where can infrared telescopes also be stationed?
In space and remote controlled from Earth
55
Where must UV positioned?
In space
56
Why can't UV telescopes be positioned on Earth?
Because the ozone layer blocks all UV rays less than 300nm
57
What configuration do ultraviolet telescopes use?
Cassegrain
58
How do gamma telescopes create images?
Don't use mirrors, use a detector made of pixels
59
What do gamma telescopes observe? (4)
Gamma ray bursts Quasars Blackholes Solar flares
60
Where do X-ray telescopes have to be stationed?
in space
61
Why do X-ray telescopes have to be stationed in space?
Because X-rays are absorbed by the atmosphere
62
What are X-ray telescopes comprised of?
A combination of parabolic and hyperbolic mirrors
63
What do X-ray telescopes usually observe? (4)
High energy areas of space: Active galaxies Blackholes Neutron stars
64
What is collecting power of a lens/mirror?
The ability to collect incident EM radiation
65
What is collecting power inversely proportional to?
the area of the objective lens
66
The greater the collecting power.....
The brighter the image produced
67
What is resolving power?
The ability of a telescopes to produce separate images of close together objects or a measure of of how much detail you can see
68
What is needed for an image to be resolved?
The angle between the straight lines from Earth to each object must be at least the minimum angle resolution
69
According to Rayleigh's criterion what causes images not to be resolved?
If any part of the central maximum of either image falls within the first minimum diffraction
70
What is collecting power proportional to?
Diameter squared
71
What does CCD stand for?
Charged-coupled devices
72
What is quantum efficiency?
the percentage of incident photons which cause an electron to be released
73
What is pixel resolution?
The number of pixels used to form an image on a screen
74
Regarding pixel resolution, what can a large amount of small pixels do that a small amount of large pixels can't?
A lot of small pixels can resolve an image more clearly than a small amount of large pixels.
75
What is spatial resolution?
The minimum distance that two objects must be apart in order to be distinguishable
76
What is spatial resolution used to do?
Observe small objects
77
What is convenience?
How easy images are to form and use
78
What is the quantum efficiency of a CCD?
Roughly 80%
79
What is the quantum efficiency of the human eye?
4-5%
80
What is the spectral range of a CCD?
IR, UV and visible
81
What is the spectral range of the human eye?
Only visible
82
What is the pixel resolution of a CCD?
Varies but is roughly 50 megapixels
83
What is the pixel resolution of the human eye?
roughly 500 mega pixels
84
What is the spatial resolution of a CCD?
10 micro metres
85
What is the spatial resolution of the human eye?
100 micro metres
86
What is the convenience of a CCD?
Needs to be set up but image produced are digital
87
What is the convenience of the human eye?
Simpler to use, no need for extra equipment
88
What are CCD's more useful for?
detecting finer details and producing images which can be shared and stored

Physics Aqa (11 decks)

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