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PHSI > Module 5: Optics > Flashcards

Module 5: Optics Flashcards

1
Q

Light is an ____ wave

A

Electromagnetic

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2
Q

Which branch of optics deals with a ray of light interacting with an object larger than its wavelength?

A

Geometric optics

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3
Q

Which branch of optics deals with a ray of light interacting with an object smaller than its wavelength?

A

Wave optics

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4
Q

Range of visible light

A

400-700nm wavelength (violet to red)

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5
Q

How does light travel in all directions from a point?

A

It is reflected at different angles by the rough surface

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6
Q

Other name for geometric optics

A

Ray optics

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7
Q

Refractive index

A

Property of a material which dictates how light behaves when passing through

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8
Q

Light always travels in _____ _____

A

Straight lines

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9
Q

Speed of light

A

3 x 10^8 ms^-1

(c)

This is constant in a vacuum, and slower through any medium

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10
Q

n of a vacuum

A

Refractive index = 1 ~ n(air)

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11
Q

Law of reflection

A

The angle of incidence is equal to the angle of reflection

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12
Q

Law of refraction

A

The change in direction depends on the relative refractive indices of the media, and the angle of the incident ray relative to the normal

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13
Q

We see objects below water at a _____ depth than they really are

A

Shallower/ smaller

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14
Q

Optical manhole

A

Light is compressed into a circle (fish eye view) when looking up form underwater

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15
Q

Total internal reflection

A

Light rays from under water are reflected back down, instead of refracting into the air

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16
Q

Why does total internal reflection occur?

A

When the incident angle is higher than the critical angle, refraction is so great the light ray bend back down

Occurs when refractive index is greater for medium one than two (e.g. from water to air)

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17
Q

At what two kinds of points do images appear?

A

Where light rays converge

Where light rays appear to diverge

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18
Q

Optical axis

A

Line running horizontally through the middle of the lens/ mirror

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19
Q

Which side are objects drawn on in ray diagrams?

A

LHS

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20
Q

What doe F represent in a ray diagram?

A

Focus/ focal point (where light rays converge/ appear to diverge)

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21
Q

Other term for convex lens

A

Converging lens

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22
Q

Other term for concave lens

A

Diverging lens

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23
Q

Focal length

A

f, distance of focal point from lens

24
Q

The larger the focal length, the _____ the lens

A

Weaker

25
Q

Optical power, O

A

Indication of how strongly rays will be bent by a lens

26
Q

Units for optical power

A

Diopters D

27
Q

Real image

A

Where light rays pass through the image point

28
Q

Virtual image

A

Where light rays do not pass through the image point

Image appears at a point where object is not

29
Q

Distance from a real image to a lens is ______

Distance from a virtual image to a lens is ______

A

Positive

Negative

30
Q

If lens is converging, f is _____

If lens is diverging, f is _____

A

Positive

Negative

31
Q

A concave lens can only form ____ images

A

Virtual

32
Q

Magnification

A

Ratio of image height to object height

If negative, image is smaller than object
If positive, image is larger than the object

33
Q

A negative magnification corresponds to ?

A

An inverted image

34
Q

Three types of mirrors

A

Planar
Concave
Convex

35
Q

Images formed by a flat mirror are always ?

A

Virtual

36
Q

What are R and C in mirrors?

A

Radius of curvature (R)

Centre of curvature (C)

37
Q

How does focal length relate to radius of curvature?

A

f = R/2

38
Q

How many focal points do mirrors and lenses have?

A

Mirrors- one

Lenses- two

39
Q

What is different about sign rules for mirrors (compared to lenses)?

A

f P and C are positive when mirror is concave, and negative when mirror is convex

40
Q

Where in the eye is light focused?

A

Retina

41
Q

How does the eye focus on objects at different distances?

A

Expands and contracts its lens for higher and lower optical powers

42
Q

di of the eye

A

2cm (from lens to retina)

43
Q

Myopia

A

A vision defect in which the eye has a far point

The image is focussed before the retina for fair objects

44
Q

How to compensate for myopia?

A

A diverging lens

Creates a virtual image closer than object

45
Q

Hypermetropia

A

Visual defect in which eye has a near point which is further away than normal

Image is focussed beyond the retina

46
Q

How do we compensate for hypermetropia?

A

Converging lens

Creates virtual image beyond the object

47
Q

Presbyopia

A

Diminished ability to accomodate that occurs with ageing

Is not a disease

48
Q

How can presbyopia be corrected?

A

Reading glasses or graduated lenses

49
Q

Astigmatism

A

Irregularities in the shape of the cornea or lens cause an image where parts are in focus and some parts aren’t

50
Q

How is astigmatism corrected?

A

By wearing lenses with opposite irregularities to the eye

51
Q

The smaller the diameter, the ____ the angle of diffraction

A

Larger

52
Q

Resolving power/resolution

A

Ability of an optical instrument to produce distinct images of objects that are very close together

53
Q

Rayleigh criteria

A

The minimum angle at which two objects are visible

54
Q

If there are two objects close together, what do we need to be able to distinguish between them?

A

Large diameter

55
Q

S = r x theta

What do the symbols mean?

A

s = distance between two objects

r = distance from observer to objects

56
Q

What effect does the earths atmosphere have on resolution?

A

Inhibits it because it refracts light entering

PHSI (6 decks)

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