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Physics AS > 2.3 Lenses > Flashcards

2.3 Lenses Flashcards

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1
Q

Lens

A

piece of transparent material that refracts light rays to form an image

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2
Q

principal axis

A

imaginary horizontal line running through optical centre of lens

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3
Q

2 types of lens

A

convex/converging
concave/diverging

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4
Q

convex/converging lens

A

converges rays of light travelling parallel to its principal axiS

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5
Q

focal point of converging/convex lens

A

point where rays converge

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6
Q

focal length

A

distance from focal point to optical centre of lens

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7
Q

concave/diverging lens

A

diverges rays of light travelling parallel to principal axis

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8
Q

focal point of diverging/concave lens

A

point where rays appear to diverge from

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9
Q

lens equation

A

1/f = 1/u + 1/v

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10
Q

what do the letters in the lens equation stand for?

A

u = object to lens
v = image to lens
f = focal length of lens

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11
Q

lens equation method

A

move lens until image is sharply focused
measure u, distance from object to lens and v, distance from image to lens
repeat to obtain series of 5 values for u and v
calculate 1/u and 1/v

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12
Q

refraction rules for converging lens - ray going to optical centre of lens

A

straight through
no refraction

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13
Q

refraction rules for converging lens - ray travelling parallel to principal axis

A

refracts
travels through focal point of lens

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14
Q

refraction rules for converging lens - ray passes through focal point on way to lens

A

refract
travel parallel to principal axis

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15
Q

refraction rules for diverging lens - ray going to optical centre of lens

A

straight through
no refraction

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16
Q

refraction rules for diverging lens - ray travelling towards focal point on opposite side of lens

A

refracts
travels parallel to principal axis

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17
Q

refraction rules for diverging lens - ray travelling parallel to principal axis

A

refracts
appears to have come from focal point on object side of lens

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18
Q

Convex lens - object beyond 2f from lens example

A

camera

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19
Q

Convex lens - object beyond 2f from lens properties

A

image is:
real
inverted
diminished
between F and 2F

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20
Q

Convex lens - object at 2f example

A

photocopier

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21
Q

Convex lens - object at 2f properties

A

image is:
real
inverted
same size as object
at 2F

22
Q

Convex lens - object between F and 2F example

A

projector

23
Q

Convex lens - object between F and 2F properties

A

image is:
real
inverted
enlarged/magnified
beyond 2F

24
Q

Convex lens - object at F

A

no image will be formed here as the rays are parallel to each other

25
Q

Convex lens - object between F and the lens example

A

magnifying glass

26
Q

Convex lens - object between F and the lens properties

A

image is:
virtual
upright
magnified
between F and 2F

27
Q

Concave lens properties

A

image is:
virtual
upright
diminished
between F and the lens

28
Q

Magnification of lens equation

A

image size/object size
image distance (v)/object distance (u)
himage/hobject

29
Q

Magnification of lens

A

compare distance of object to optical centre of lens with distance of image to optical centre of lens

30
Q

sign conventions for f

A
  • for convex
    + for concave
31
Q

sign conventions for v

A

+ for real image and opposite side of lens
- for virtual image and object’s side of lens

32
Q

power of lens unit

A

diopters
D

33
Q

power of lens equation

A

1/focal length (m)

34
Q

power of concave diverging lens

A

negative

35
Q

power of convex/converging lens

A

positive

36
Q

What type of lens is in the eye?

A

Convex/converging lens

37
Q

Near point

A

Closest distance at which eye can focus on an object

38
Q

Near point for normal eye

A

25cm

39
Q

Far point

A

Furthest point that the eye can focus on

40
Q

Far point for normal eye

A

Infinity

41
Q

Accomodation

A

Adjustment that the eye makes to change the power of a lens so that there is a sharp image on the retina

42
Q

2 defects of vision

A

Myopia
Hypermetropia

43
Q

Myopia

A

Short sighted
Far objects appear blurred
Light rays converge at a point before reaching the retina instead of focusing on the retina
Image of far objects formed in front of retina

44
Q

Causes of myopia

A

Cornea curved too much
Lens is too powerful
Eye linger than usual

45
Q

Correction of myopia

A

Diverging/concave lens

46
Q

U and v values for myopia

A

Lens must produce image of object at infinity at person’s far point
U = far point - infinity
V = person’s unaided far point - negative as virtual and on same side as object

47
Q

Hypermetropia

A

Long sight
Nearby objects appear blurred, distance objects = clearer
Light rays would not converge until point behind retina

48
Q

Hypermetropia causes

A

Lens in eye not powerful enough
Eye shorter than normal

49
Q

Hypermetropia correction

A

Converging/convex lens

50
Q

U and v values for Hypermetropia

A

Far point = infinity
Near point = more than 25cm
Corrective lens used to make object at 25cm appear (virtual image) at near point
U = 25cm
V = - (their near point) - negative as virtual image

Physics AS (8 decks)

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