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MED-101 Medical Physics > THIN LENSES > Flashcards

THIN LENSES Flashcards

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1
Q
  1. What can be said about Converging Lenses?
A
  • these lenses are positive
  • the lenses are thicker at the centre than at the rim
  • these lenses converge a beam of parallel light to a
    real focus
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2
Q
  1. What can be said about Diverging Lenses?
A
  • these lenses are negative
  • they are thinner at the centre than at the rim
  • these lenses diverge a beam of parallel light from a
    virtual focus
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3
Q
  1. What is the Focal Point of a thin lens with spherical surfaces?
A
  • this is the point where the rays parallel to and near the
    central axis are brought to a focus
  • a central axis is also known as an Optical axis
  • this point is represented by the symbol f
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4
Q
  1. What can be said about the focus for converging and diverging lenses?
A

CONVERGING LENSES:
- the focus is real

DIVERGING LENSES:
- the focus is virtual

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5
Q
  1. What is the Focal Length?
A
  • it is represented by a symbol f
  • it is the distance of the principal focus from the lens
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6
Q
  1. What is the result of each lens being reversed without altering the rays?
A
  • two symmetric focal points will exist for each lens
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7
Q
  1. What do all the rays that pass through the lens form?
A
  • they form an image of a positive distance (d2) to the
    right of the lens
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8
Q
  1. What is the chemical equation to work out d2?
A
  • it is given by the Lens Equation
  • d1= distance the object has to the lens
  • d2= distance the lens has to the real image
  • f = focal length
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9
Q
  1. Where does a real image form?
A
  • a real image forms at d2
  • it does this when d1 is greater than f

WE WILL SEE AN IMAGE AT D2:
- if you place a screen at that point
- such as a piece of paper

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10
Q
  1. What happens when an image is inverted?
A
  • its size will be magnified
  • its size is represented by the symbol y2
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11
Q
  1. How do we calculate Magnification?
A

M = magnification
di,0,1,2 = distances
y1,y2= vertical heights of the object and the image

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12
Q
  1. What can be said about the 2 images?
A

THE 2ND IMAGE:
- is converging
- this is a real image
- this is the creation of a real inverted image

THE 1ST IMAGE:
- it is located outside of the focus

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13
Q
  1. What do Converging lenses form?
A
  • inverted real images of objects
  • they are located outside the principal focus
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14
Q
  1. What happens when the object is between the principal focus and the lens?
A
  • the image is then virtual
  • it is on the same side of the lens as the object is
  • the image is erect and enlarged

A VIRTUAL IMAGE IS:
- up right image
- it has a + magnification

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15
Q
  1. What happens in Diverging lenses when it comes to magnification?
A
  • the diverging lenses produce only virtual images
  • these are erect
  • they are smaller images of real objects
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16
Q
  1. When it comes to the drawing of all figures, where is light initially travelling from?
A
  • it travels from left to right
  • the object is to the left of the lens originally
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17
Q
  1. What can be said about the distance form the object to a lens?
A
  • it is positive

THE DISTANCE FROM A LENS TO A REAL IMAGE:
- this is positive
- the real image is located to the right of the lens

THE DISTANCE FROM A LENS TO A VIRTUAL IMAGE:
- this is negative
- the image is located to the left of the lens

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18
Q
  1. What can be said about f (Focal Point) for a converging (convex) lens?
A
  • f is positive
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19
Q
  1. What can be said about f (Focal Point) for a concave (diverging) lens?
A
  • f is negative
20
Q
  1. What are the positive lenses of the eye?
A
  • the cornea
  • the crystalline lens
  • they form real images
  • they form them on the Retina
21
Q
  1. What can be said about Corrective lenses?
A
  • eyeglass lenses and contact lenses are examples of
    corrective lenses
  • they can have positive and negative focal lengths
  • this depends on the necessary correction needed
22
Q
  1. Which kind of corrective lens is used to treat Presbyopia?
A
  • a lens with a positive focal length

PRESBYOPIA= gradual loss of your eyes’ ability to focus
on nearby objects

23
Q
  1. What kind of corrective lens is used to treat Myopia?
A
  • a lens with a negative focal length

MYOPIA = a common vision condition in which near
objects appear clear, but objects farther away
look blurry

24
Q
  1. What are focal lengths expressed as?
A
  • they are expressed as distances
  • they are expressed in cm or in m
25
Q
  1. How would we calculate the power of a lens?
A
  • this is the inverse of the focal length calculation
  • P = 1 / f
    P= power of the lens
    f= focal length (cm or m)

LENS POWER IS MEASURED IN:
- Diopters (D)
- 1D = 1/m

26
Q
  1. What happens when there are two refracting interfaces in succession?
A
  • we use the Lensmaker’s Equation
  • n = refractive index of the lens material
  • r1= radii of the curvature of lens surface one
  • r2= radii of the curvature of lens surface two
  • this equation holds for all the types of thin lenses
27
Q
  1. When is the radius of the curvature (r) positive?
A
  • it is positive when its centre of curvature lies to the
    right of the surface
28
Q
  1. When is the radius of the curvature (r) negative?
A
  • this is when the centre of the curvature lies to left of
    the surface
29
Q
  1. Does this make sense?
A
  • yes
30
Q
  1. Can lenses have a range of shapes?
A
  • yes they can
  • even if they have the same focal length
31
Q
  1. What are the shapes of the lenses when they have positive focal lengths?
A
  • they can be biconvex
  • they can be planoconvex (one side flat)
  • they can be positive meniscus
32
Q
  1. What are the shapes of the lenses when they have negative focal lengths?
A
  • they can be biconcave
  • they can be planoconcave (one side flat)
  • they can be negative meniscus
33
Q
  1. What can be said about the shape of the isolated cornea lens?
A
  • it is a negative meniscus lens
  • it has a negative focal length
34
Q
  1. What can be said about the shape of the Crystalline lens?
A
  • it is an asymmetric biconvex lens
  • it has a positive focal length
35
Q
  1. How do we work out the focal length (f) for a combination of two thin lenses?
A
  • lens 1 has a focal length of f1
  • lens 2 has a focal length of f2
36
Q
  1. Answer this question.
A
  • B
37
Q
  1. Answer this question.
A
  • B
  • length that is propagated into empty space
  • s = d / t
    = 80 / 67 x 10⎺³
    = 2.0 x 107 m
38
Q
  1. Answer this question.
A
  • D
39
Q
  1. Read through Summary 1.
    Does everything make sense?
A
  • yes
40
Q
  1. Read through Summary 2.
    Does everything make sense?
A
  • yes
41
Q
  1. Read through Summary 3.
    Does everything make sense?
A
  • yes
42
Q
  1. Read through Summary 4.
    Does everything make sense?
A
  • yes
43
Q
  1. Read through Summary 5.
    Does everything make sense?
A
  • yes
44
Q
  1. Read through Summary 6.
    Does everything make sense?
A
  • yes
45
Q
  1. Read through Summary 7.
    Does everything make sense?
A
  • yes
46
Q
  1. Read through Summary 8.
    Does everything make sense?
A
  • yes

MED-101 Medical Physics (21 decks)

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