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LC Physics > Lenses Chapter 5 > Flashcards

Lenses Chapter 5 Flashcards

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1
Q

Is a convex lens converging or diverging

A

Converging

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2
Q

Is a concave lens converging or diverging

A

Diverging

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3
Q

Describe what a convex lens looks like

A

Thick at the center and thinner at the sides.

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4
Q

Describe what a concave lens looks like

A

Thicker at the ends than in the centre (caves in)

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5
Q

What is the optic centre

A

Centre of the lens

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6
Q

What is the principal axis

A

Straight line that passes through the optic centre and hits the lens at ninety degrees

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7
Q

What is the focus

A

Point to which parallel beams to the axis converge to or appear to have converged from (for concave)
There are two focuses one for each side of lens

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8
Q

What is the focal length

A

Distance from the optic centre to the focus

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9
Q

How does a lens refract a ray which strikes the optic centre

A

It passes straight through the mirror

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10
Q

How does a lens refract a ray which strikes the lens travelling parallel to the axis

A

It travels through the focus on the other side of the lens

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11
Q

How does a lens refract a ray which strikes the lens after having passes through the focus

A

it emerges parallel to the principal axis

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12
Q

Explain real image

A

Image formed by the actual intersection of light rays

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13
Q

Explain virtual image

A

Image formed by the apparent intersection of light rays

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14
Q

Explain what an image will look like for a convex lens outside the focus (between 2F and F)

A

Image is real, on the other side of the lens to the object and it is inverted and magnified

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15
Q

Explain what an image will look like for a convex lens outside the focus (at 2F)

A

Image is real, on the other side of the lens to the object, inverted and same size

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16
Q

Explain what an image will look like for a convex lens outside the focus (Outside 2F)

A

Image is real, on the other side of the lens to the object, inverted and diminished

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17
Q

Explain what an image will look like for a convex lens at the focus

A

Image is virtual but at your blind spot. You will never see this image.

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18
Q

Explain what an image will look like for a convex lens inside the focus

A

Image is virtual and on the same side of the lens a the object. Image is erect and magnified.

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19
Q

Give two uses of convex lenses

A

microscopes and magnifying glasses

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20
Q

What is the formula for magnification

A

v/u - image height/object height

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21
Q

What is the formula to use for a convex mirror

A

1/u + 1/v = 1/f

22
Q

How can you tell from the formula if an image is real or virtual and formed in a convex or concave lens

A

v is + for real image
v is - for virtual image
f is + for convex
f is - for concave

23
Q

What is u in formula

A

distance from optic centre to object

24
Q

What is v in formula

A

distance from optic centre to image

25
Q

Explain how light refracts by a concave lens when it strikes the optic centre

A

Ray passes straight through the lens

26
Q

Explain how light refracts by a concave lens when ray is heading for the focus when it strikes the lens

A

It emerges parallel to the principal axis

27
Q

Explain how light refracts by a concave lens that is travelling parallel to the axis

A

It refracts as if it came from the focus.

28
Q

Describe an image in a concave mirror

A

Virtual, on the same side of the lens as the object, erect and diminished

29
Q

How does the distance from the concave effect the image

A

The nearer the object to the lens the bigger it is.

30
Q

What is the formula for a concave lens

A

1/u - 1/v = -1/f

31
Q

What is the relationship with the focal length of a lens and it’s power

A

a short focal length has a greater converging effect on a light beam and therefore has a larger power than a longer focal length

32
Q

What is the formula for the power of a lens

A

1/focal length

33
Q

Is the power of the concave lens positive or negative

A

negative

34
Q

Is the power of the convex lens positive or negative

A

positive

35
Q

What is the unit of the power of the lens

A

per metre (m to the power of -1)

36
Q

How is the power of a combination of lenses found

A

P=P1+P2

sums of the powers

37
Q

How is the focal length of a combination found

A

1/f = 1/f1 + 1/f2
where f is positive for a convex lens
where f is negative for a concave lens

38
Q

What is the iris

A

The iris controls the amount of light entering the eye by making the pupil larger or smaller

39
Q

Explain the focusing system of the eye

A

The cornea and crystalline lens form a converging system. The aqueous and vitreous humour (liquids) also form part of the system to focus light onto the back of the eye

40
Q

What is the retina

A

a light sensitive screen at the back of the eye

41
Q

How does the retina allow us to see

A

Light strikes the retina and electrical messages are sent to the brain by the optic nerve. Results in sight. If image focuses in front or behind the retina the image is blurred

42
Q

What is the power of accommodation

A

Ability to focus a real image on the retina

43
Q

How does the eye focus an image

A

The ciliary muscles change the shape of the lens and hence the focal length. Object viewed from a large distance in a normal eye the object is viewed with the ciliary muscles relaxed. Lens is thinnest with greatest focal length

44
Q

Explain least distance of distinct vision

A

Near point- the smallest distance between an object and the eye where the object is seen clearly without strain.

45
Q

Explain short sighted

A

A short sighted person can see nearby objects clearly but cannot bring distant objects into focus

46
Q

Explain long sighted

A

A long sighted person can see distant objects clearly but cannot bring nearby objects into focus

47
Q

What lens corrects short sightedness

A

concave

48
Q

What lens corrects long sightedness

A

convex

49
Q

Use of a concave lens

A

Binoculars, telescopes, high quality cameras

50
Q

use of convex lens

A

binoculars, refracting telescopes, magnification

LC Physics (9 decks)

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