Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Physics > Telescopes COPY > Flashcards

Telescopes COPY Flashcards

You may prefer our related Brainscape-certified flashcards:
Physics 101 flashcards AP® Physics flashcards
1
Q

Define the Rayleigh criterion for two objects

A

Two objects can just be resolved when the central maximum of the diffraction pattern of one coincides with the first minimum of the other.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Why is IR astronomy useful?

A
  • It can detect astronomical objects that are not hot enough to emit visible or UV radiation
  • Passes through interstellar and intergalactic gas and dust more easily than light
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the quantum efficiency for the eye?

A

About 1%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the bonuses of a reflecting telescope having a greater size?

A
  • Greater collectiing power which means brighter images
  • Higher resolving power which means that objects in the sky which are close together can be seen separately more easily
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Why is the resolving power always worse for a radio telescope compared to a light telescope?

A

The wavelength of radio waves are much larger than for light waves

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the equation for resolving power?

A

ø = lambda / D

D = (aperture of lens / diameter of mirror)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Draw the ray diagram for the Astronomical Telescope

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What equation includes the angle subtended by the object, the distance from the object and the observer and the diameter of the object?

A

ø (angle subtended)= s (diameter) / r (distance)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the equation for angular magnification?

A

Angle subtended by the image at the (øi)/ angle subtended by the object at the unaided eye (øo)

or

FO/Fe

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the resolving power of the Jodrell Bank telescope whose diameter is 75m and has radiowaves of wavelength 10m

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

How can radio telescopes be made lighter?

A
  • Use wire mesh (have a reflecter with holes in it)
  • As long as holes are smaller than lambda/20 in size the image is unaffected
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is chromatic aberration?

A

Where different wavelengths are refracted by a different amount.

Blue light is refracted more than red so it is brought to focus closer to the lens than red - it has a shorter focal length

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Compare UV telescopes to light telescopes

A
  • UV has a shorter wavelength then light and so has a better resolving power
  • The UV telescope will need to be smoother
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is resolving power measured in?

A

Radians

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the disadvantages of a reflecting mirror? (2)

A

The secondary mirror blocks some light this:

  • Lowers brightness

The secondary mirror causes some diffraction of the light which:

  • Decreases the sharpness
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

A telescope has an eyepiece of focal length 5 cm and an objective of focal length 50 cm. What angle will the moon subtend if viewed through the telescope? The diameter of the mooon = 3.5 x10^3 km. Distance of moon from earth = 384.4 x10^3 km

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What are the similarities between optical and radio telescopes? (2)

A
  • Both use a parabolic reflector to focus waves
  • Both need to be sited away from pollution, humidity and away from other sources of interference
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Define the focal length

A

The distance between the focal point and the centre of the lens

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What are the differences between optical and radio telescopes? (7)

A
  • Radio telescopes can be used during the day ans when it is cloudy
  • Light telescopes produce a whole image whereas radio telescopes cannot produce an image
  • Radio telescopes are longer
  • Radio telescopes have one relfectin surface but light telescopes have two
  • Radio have a greater surface area to improve resolving power amd due to radio signals being weaker
  • Optical always has a better resolving power
  • Radiowaves can penetrate dust
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Define the collecting power of a radio telescope

A

The energy it collects per second

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Draw the diffraction pattern through a circular aperture

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Why do radio waves need to be focused by the reflector

A

Otherwise they are very weak and focusing makes them more intense.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Draw a labelled diagram showing chromatic aberration on a lens

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What waves are allowed through our atmosphere?

A
  • Visible waves
  • Some UV
  • Some infra-red
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Why do IR telescopes need to be cooled?

A

IR Telescopes will detect IR from the telescope itself

It is cooled to near to absolute 0 to lower the unwanted signal

26
Q

Draw the ray diagram for a reflecting telescope

A
27
Q

What is a CCD?

A
  • A silicon chip
  • Divided into pixels
  • When a photon hits a pixel, an electron is released
  • No. of e- is proportional to the intensity of the light
  • Charge is processed to give an image
28
Q

Why is a higher quantum efficiency more favourable?

A

Images will be brighter

29
Q

What does the phrase ‘normal adjustment’ mean for an astronomical telescope?

A

The rays emerging from the telescope are parallel to each other.

30
Q

Compare the CCD to the eye

A
  • The quantum efficiency is greater so images will be brighter
  • CCD can detect a wider range of the EM spectrum
  • CCDs have better resolution
  • CCD is more convenient as data can be passed straight into a computer
  • Eye is quicker
31
Q

What does it mean to say that our atmosphere is transparent to certain wavelengths?

A

It lets in certain wavelengths

32
Q

Why is a large area needed for a radio telescope?

A
  • To increase collecting power which increases image brightness
33
Q

Define Principle axis

A

The line passing perpendicularly through the middle of the lens

34
Q

Draw a ray diagram that shows sperical aberration

A
35
Q

A telescope is described as having a 127mm aperture and a resolving power of 0.9 arc seconds. What wavelength have the manufacturers used to calculate the resolving power?

A
36
Q

What does chromatic aberration cause?

A

The image to have coloured edges

37
Q

What is an advantage if IR radiation over radio telescopes?

A

The resolving power is greater as IR wavelengths are much shorter (but not as god as light telescopes)

38
Q

Why are IR telescopes located at the top of mountains/in space?

A

Water vapor absorbs IR radiation

Having them high up minimises this

39
Q

Define resolving power

A

The minimum angle in radians which can be resolved

40
Q

Is a greater or smaller resolving power better?

A

Smaller

41
Q

What is UV absorbed by in out atmosphere?

A

Ozone

42
Q

What type of light has a shorter focal length on a refracting telescope?

A

Blue light

43
Q

What is the collecting power of a radio telescope equal to?

A

The area of the telescope

44
Q

What is the quantum efficiency for a CCD?

A

Greater than 80%

45
Q

Why are telescopes put at high altitudes, in places of low humidity, well away from cities and away from sources of chemical pollution?

A

Pollution and humidity will reduce the intensity of the radiation.

Radio signals from mobiles can cause interference so need to be well away from cities.

46
Q

What assumption is made with the astronomical telescope?

A

The image is upside down

47
Q

What are the advantages to reflecting telescopes compared to refracting telescopes

A
  • Mirrors can be made larger, as they can be supported from behind, unlike lenses which have to be supported from the edges
  • Lenses have chromatic aborration, but mirrors dont
  • Lenses and mirrors have spherical aborration but it is easier to reduce it in mirrors
  • The glass of a lens can block some wavelengths of EM radiation. Impurities in the glass can also lower the intensity of the light. This doesnt happen with mirrors.
48
Q

Draw the ray diagram for a parabolic reflector

A
49
Q

How much more powerful is the largest radio telescope in the world with a diameter of 305m than the one at Jodrell Bank with a diameter of 75m?

A
50
Q

Where does a UV telescope need to be sited?

A

In space so the UV cannot be absorbed by ozone

51
Q

Define an Airy Disk

A

The bright central maximum of the diffraction pattern formed when light passes through a circular aperture

52
Q

How do you reduce spherical aberration in reflecting and refracting telescopes?

A

Make the mirror/lens more parabolic

It is easier to make a mirror more parabolic than a lens

53
Q

A telescope with a mirror of diameter 40cm is used to view objects emitting light with a typical wavelength of 500nm. Calculate the resolving power of this telescope.

A
54
Q

Define quantum efficiency

A

The percentage of the number of photons falling on a device which produce a signal to the total number of photons falling on the device

55
Q

What is infra-red absorbed by in our atmosphere?

A

Water Vapour

56
Q

What can you study with X-Ray Telescopes?

A

Violent and energetic events in the universe

57
Q

Where do X-Ray Telescopes need to be sited?

A

Above the atmosphere

58
Q

A telescope is 1.50m long and has a magnification of 50. What are the values of the focal lengths of the objective and the eyepiece?

A
59
Q

Draw the ray diagram for a Cassegrain telescope / reflecting telescope

A
60
Q

describe the setup of a radio telescope

A
  • Parabolic dish
  • Reflects radio waves to an antenna at the principle focus
  • The reciever has to be tuned in
61
Q

Define the focal point/the principle focus

A

The point on the Principle axis through which all rays parallel to the Principle axis pass after being refracted by the lens

62
Q

What does it mean to say that our atmosphere is opaque to certain wavelengths?

A

It blocks certain wavelengths

Physics (15 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions