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-P7- > P7.2 > Flashcards

P7.2 Flashcards

1
Q
  1. What is the speed of waves affected by?
A

-the medium they are travelling through

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2
Q
  1. When will wave speed change?
A

-if a wave moves from one medium into another

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3
Q
  1. What does a change in the speed of a wave cause? Why?
A

-a change in wavelength
-the frequency of the waves cannot change (wave speed=frequency x wavelength)
=may cause a change in direction (refraction)

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4
Q
  1. What would happen if the speed decreases?
A

-the wavelength would decrease

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5
Q
  1. What is refraction?
A

-change in direction of a wave

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6
Q
  1. How can refraction of light waves be explained?
A

-a change in their speed when they pass into a different medium= refraction of light waves

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7
Q
  1. What happens if a light ray hits a boundary (change in medium) straight on?
A
  • slows, same direction

- same frequency, shorter wavelength

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8
Q
  1. What happens if a light ray hits a boundary (change in medium) at an angle?
A

-part slows while the other part is still going fast= change direction

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9
Q
  1. What do convex/converging lenses use refraction for?
A

-to focus light waves to form an image of an object

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10
Q
  1. What happens in a converging lens?
A

-light ray hits surface
=air to glass= slows= bends towards the normal
-light comes out of lens
=glass to air= speeds up= bends away from normal
-curvature of lens= parallel rays bend towards focal point= image is formed

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11
Q
  1. What is the normal?
A

-the line at right angles to the boundary at the point where the ray enters or leaves

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12
Q
  1. What shape is a converging lens?
A
  • it is convex

- fatter towards the middle

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13
Q
  1. What do converging lenses do to rays of light?
A

-cause them to converge at a focus

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14
Q
  1. What is a principal axis?
A

-a line which passes straight through the lens

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15
Q
  1. What is the focal point of a lens?
A

-where rays initially parallel to the principle axis meet

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16
Q
  1. Where are focal points positioned?
A

-in front and behind the lens

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17
Q
  1. What is the focal length?
A

-the distance between the middle of the lens and its focal point

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18
Q
  1. What is the relationship between focal length and power?
A

-shorter focal length= converges more strongly= more powerful

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19
Q
  1. How do you make a more powerful lens from the same material?
A

-make it with a more strongly curved surface

20
Q
  1. What is the unit of lens power?
A

-D, dioptres

21
Q
  1. What is focal length measured in?
A

-m, meters

22
Q
  1. How does light from astronomical objects reach the earth?
A

-as effectively parallel sets of rays

23
Q
  1. Why does light from astronomical objects reach the earth as effectively parallel sets of rays?
A

-the astronomical objects are so distant

24
Q
  1. What does a simple optical telescope have?
A

-two converging lenses of different powers, with the more powerful lens as the eyepiece

25
Q
  1. How is the eyepiece lens made more powerful?
A

-it is more curved

26
Q
  1. How is a simple optical telescope set up?
A

-lenses aligned on the principal axis so focal point the same

27
Q
  1. What is a telescopes two optical elements?
A
  • objective lens or mirror

- an eyepiece

28
Q
  1. What is the purpose of the objective lens or mirror?
A

-collect light from the object being observed and form an (REAL) image of it

29
Q
  1. What is the purpose of the eyepiece?
A

-produces a magnified image (VIRTUAL) of the image from the objective that we can view

30
Q
  1. What do most astronomical telescopes have as their objectives?
A

-concave mirrors instead of converging lenses

31
Q
  1. Why do most astronomical telescopes concave mirrors instead of converging lenses as their objectives?
A
  • smoother so less distorted images
  • can reflect more types of em radiation
  • mirrors reflect rays of colours the same way
32
Q
  1. How do concave mirrors bring a parallel beam of light to a focus?
A

-parallel rays of light shine on concave mirror, then reflect and converge

33
Q
  1. Why are large telescopes needed to collect the weak radiation from faint or very distant sources?
A
  • need a huge objective lens or mirror to collect enough radiation as little radiation reaches us
  • diameter of objective lens= aperture
  • bigger aperture= more radiation= better image formed
34
Q
  1. What is an aperture?
A

-diameter of an objective lens

35
Q
  1. What is diffraction?
A

-when waves spread out from a narrow gap

36
Q
  1. What can be diffracted?
A

-light

37
Q
  1. When is the effect of diffraction on light most noticeable?
A

-when light travels through a very small gap, comparable to the wavelength of the wave

38
Q
  1. Under what circumstances is a wave diffracted most?
A

-narrower gap or longer wavelength

39
Q
  1. What size must the aperture of a telescope be?
A

-aperture must be larger than wavelength of the radiation detected by the telescope= sharp images

40
Q
  1. What happens if the size of the aperture of a telescope is smaller than the wavelength of radiation detected?
A

-diffraction causes images to blur

41
Q
  1. How can a spectrum be produced by refraction in a prism?
A
  • white light disperses as it enters the prism
  • different wavelengths of coloured light refract by different amounts
  • boundaries aren’t parallel so different wavelengths don’t recombine like they would in a rectangular prism= rainbow not white light
42
Q
  1. What is white light?
A

-a mixture of lots of wavelengths of coloured light

43
Q
  1. How can a spectrum be produced?
A

-by a diffraction grating

44
Q
  1. What does a diffraction grating produce?
A

-a spectrum

45
Q
  1. What is a diffraction grating?
A

-has very narrow slits that diffract light

46
Q
  1. How does a diffraction grating make a spectrum?
A
  • light passes through gaps

- different wavelengths of coloured light diffract by different amounts= spectrum of coloured light

47
Q
  1. What are spectra from a diffraction grating used for?
A

-to analyse light coming from stars

-P7- (6 decks)

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