Module 5: Optics Flashcards
Light is an ____ wave
Electromagnetic
Which branch of optics deals with a ray of light interacting with an object larger than its wavelength?
Geometric optics
Which branch of optics deals with a ray of light interacting with an object smaller than its wavelength?
Wave optics
Range of visible light
400-700nm wavelength (violet to red)
How does light travel in all directions from a point?
It is reflected at different angles by the rough surface
Other name for geometric optics
Ray optics
Refractive index
Property of a material which dictates how light behaves when passing through
Light always travels in _____ _____
Straight lines
Speed of light
3 x 10^8 ms^-1
(c)
This is constant in a vacuum, and slower through any medium
n of a vacuum
Refractive index = 1 ~ n(air)
Law of reflection
The angle of incidence is equal to the angle of reflection
Law of refraction
The change in direction depends on the relative refractive indices of the media, and the angle of the incident ray relative to the normal
We see objects below water at a _____ depth than they really are
Shallower/ smaller
Optical manhole
Light is compressed into a circle (fish eye view) when looking up form underwater
Total internal reflection
Light rays from under water are reflected back down, instead of refracting into the air
Why does total internal reflection occur?
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)
At what two kinds of points do images appear?
Where light rays converge
Where light rays appear to diverge
Optical axis
Line running horizontally through the middle of the lens/ mirror
Which side are objects drawn on in ray diagrams?
LHS
What doe F represent in a ray diagram?
Focus/ focal point (where light rays converge/ appear to diverge)
Other term for convex lens
Converging lens
Other term for concave lens
Diverging lens
Focal length
f, distance of focal point from lens
The larger the focal length, the _____ the lens
Weaker
Optical power, O
Indication of how strongly rays will be bent by a lens
Units for optical power
Diopters D
Real image
Where light rays pass through the image point
Virtual image
Where light rays do not pass through the image point
Image appears at a point where object is not
Distance from a real image to a lens is ______
Distance from a virtual image to a lens is ______
Positive
Negative
If lens is converging, f is _____
If lens is diverging, f is _____
Positive
Negative
A concave lens can only form ____ images
Virtual
Magnification
Ratio of image height to object height
If negative, image is smaller than object
If positive, image is larger than the object
A negative magnification corresponds to ?
An inverted image
Three types of mirrors
Planar
Concave
Convex
Images formed by a flat mirror are always ?
Virtual
What are R and C in mirrors?
Radius of curvature (R)
Centre of curvature (C)
How does focal length relate to radius of curvature?
f = R/2
How many focal points do mirrors and lenses have?
Mirrors- one
Lenses- two
What is different about sign rules for mirrors (compared to lenses)?
f P and C are positive when mirror is concave, and negative when mirror is convex
Where in the eye is light focused?
Retina
How does the eye focus on objects at different distances?
Expands and contracts its lens for higher and lower optical powers
di of the eye
2cm (from lens to retina)
Myopia
A vision defect in which the eye has a far point
The image is focussed before the retina for fair objects
How to compensate for myopia?
A diverging lens
Creates a virtual image closer than object
Hypermetropia
Visual defect in which eye has a near point which is further away than normal
Image is focussed beyond the retina
How do we compensate for hypermetropia?
Converging lens
Creates virtual image beyond the object
Presbyopia
Diminished ability to accomodate that occurs with ageing
Is not a disease
How can presbyopia be corrected?
Reading glasses or graduated lenses
Astigmatism
Irregularities in the shape of the cornea or lens cause an image where parts are in focus and some parts aren’t
How is astigmatism corrected?
By wearing lenses with opposite irregularities to the eye
The smaller the diameter, the ____ the angle of diffraction
Larger
Resolving power/resolution
Ability of an optical instrument to produce distinct images of objects that are very close together
Rayleigh criteria
The minimum angle at which two objects are visible
If there are two objects close together, what do we need to be able to distinguish between them?
Large diameter
S = r x theta
What do the symbols mean?
s = distance between two objects
r = distance from observer to objects
What effect does the earths atmosphere have on resolution?
Inhibits it because it refracts light entering
