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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
10. How is the eyepiece lens made more powerful?
-it is more curved
26
10. How is a simple optical telescope set up?
-lenses aligned on the principal axis so focal point the same
27
11. What is a telescopes two optical elements?
- objective lens or mirror | - an eyepiece
28
11. What is the purpose of the objective lens or mirror?
-collect light from the object being observed and form an (REAL) image of it
29
11. What is the purpose of the eyepiece?
-produces a magnified image (VIRTUAL) of the image from the objective that we can view
30
13. What do most astronomical telescopes have as their objectives?
-concave mirrors instead of converging lenses
31
13. Why do most astronomical telescopes concave mirrors instead of converging lenses as their objectives?
- smoother so less distorted images - can reflect more types of em radiation - mirrors reflect rays of colours the same way
32
14. How do concave mirrors bring a parallel beam of light to a focus?
-parallel rays of light shine on concave mirror, then reflect and converge
33
15. Why are large telescopes needed to collect the weak radiation from faint or very distant sources?
- 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
15. What is an aperture?
-diameter of an objective lens
35
16. What is diffraction?
-when waves spread out from a narrow gap
36
18. What can be diffracted?
-light
37
18. When is the effect of diffraction on light most noticeable?
-when light travels through a very small gap, comparable to the wavelength of the wave
38
18. Under what circumstances is a wave diffracted most?
-narrower gap or longer wavelength
39
19. What size must the aperture of a telescope be?
-aperture must be larger than wavelength of the radiation detected by the telescope= sharp images
40
19. What happens if the size of the aperture of a telescope is smaller than the wavelength of radiation detected?
-diffraction causes images to blur
41
20. How can a spectrum be produced by refraction in a prism?
- 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
20. What is white light?
-a mixture of lots of wavelengths of coloured light
43
21. How can a spectrum be produced?
-by a diffraction grating
44
21. What does a diffraction grating produce?
-a spectrum
45
21. What is a diffraction grating?
-has very narrow slits that diffract light
46
21. How does a diffraction grating make a spectrum?
- light passes through gaps | - different wavelengths of coloured light diffract by different amounts= spectrum of coloured light
47
21. What are spectra from a diffraction grating used for?
-to analyse light coming from stars

-P7- (6 decks)

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