L1- fundamentals of geometrical optics

Question 1

what is light?

Answer 1

. light is a form of radiant energy
. comes from sun or candle
. smallest quantity of energy that can be transported ( photon )
. wave-particle duality- consider light as a particle using a wave theory

Question 2

what are the main properties of light?

Answer 2

. velocity
. wave length
. frequency
. speed ( 3x10^8) m/s
. polarization
. intensity

Question 3

what does the sun emit?

Answer 3

white light - which is a combination of all colours on the electromagnetic scale.(400( ultraviolet(shorter) ) -700nm( Infrared- longer) )

Question 4

what are the 2 basic rules of geometrical optics ?

Answer 4

. light travels in the forms of rays that are coming from source of light
. a ray of light travels in a straight line until it meets an optical boundary

Question 5

how would you see a red pencil?

Answer 5

. the sun emits white light
. dyes on surface of pencil only reflect back red light and absorb all other colours
. only red rays are re-emitted and reach observer eye

Question 6

what does monochromatic mean?

Answer 6

single wavelength

Question 7

what does poly chromatic mean ?

Answer 7

many wavelength

Question 8

what is black ?

Answer 8

absence of colour

Question 9

what happens when light crosses an interface between two transparent media?

Answer 9

when light travels from air to glass
the wavefronts are closer together in glass, which suggests slowing down of light within the medium
light will travel slower in glass because its more optically dense than air
(v is smaller than c)

Question 10

what is the relation between density and speed of light ?

Answer 10

the more optically dense a medium (than air )is the slower light will travel through it

Question 11

why do rays bend?

Answer 11

rays bend as they cross an optical surface between two transparent media with two different optical density

Question 12

what happens to the wave front as it crosses the interface?

Answer 12

. bottom part of wavefront will hit this speed restriction earlier than top part of wavefront

. as wave front crosses interface the bottom part is travelling slower than the top part and will lag down
. when wavefront crosses boundary both top and bottom part will travel at same speed

Question 13

why do wave front tilt when crossing air-glass interface?

Answer 13

.wave front has been tilted because of the uneven slowing as it crosses the air-glass interface
. light travels in a different direction after crossing interface

Question 14

what is refraction?

Answer 14

bending of light rays when they cross an optical surface between media with different optical density

Question 15

why does a pencil look bent in water

Answer 15

. light rays from the bit of pencil under water will intersect in a different location than light rays from portion of pencil that extends above water
. this is why bit of pencil under water appears to be in a different location that portion of pencil that extend above water

Question 16

what is snell’s law of refraction ?

Answer 16

n sin i = n' sin i'
n= refractive index before refraction 
i=  angle of incidence
n'= refractive index after refraction
i'= angle of refraction

Question 17

where is angle i ?

Answer 17

angle between incident ray of light ( ray travelling towards surface ) and normal to surface

Question 18

where is normal line drawn ?

Answer 18

drawn where light intersects surface

Question 19

where is angle i’ ?

Answer 19

angle between refractive ray of light ( ray travelling away from surface ) and normal

Question 20

what is refractive index of air?

Answer 20

1

Question 21

what does a higher refractive index mean?

Answer 21

higher refractive index more dense a material

Question 22

what does snell’s law tell us ?

Answer 22

• the amount of refraction we get

- how much a ray bends depends on the difference between refractive indices in their two medium

Question 23

how are prisms used in optometry?

Answer 23

. to alter apparent location of an object
. sometimes an image what one eye sees is not in line with what the other eye sees
. a lens with prism will bring image into binocular synch with image seen by other eye
. used to treat double vision

Question 24

how are objects viewed through a prism displaced?

Answer 24

. objects viewed through prism are displaced through apex of prism away from base

Question 25

what is the amount of displacement in a prism dependent on ?

Answer 25

.the size of angle of apex
greater angle=thicker prism
. thicker prism= stronger correction and displaces object to greater degree
. thinner prisms= weaker amount of correction and displace object to lesser degree

Question 26

why does blue light refract more than red light?

Answer 26

. shorter wavelength

. higher refractive index

Question 27

What is the property of light that determines colour?

Answer 27

wavelength

Question 28

What should waves and rays do?

Answer 28

waves and rays must intersect at right angles

Question 29

what is visible light ?

Answer 29

• part of electromagnetic spectrum and ranges from 400nm to 700nm
• lies between IR and UV
• human eye can detect

Question 30

where do rays and wavefront intersect ?

Answer 30

rays and wavefront intersect at right angle to one another

Question 31

What are photons?

Answer 31

individual particles of light

Question 32

What is the intersection of a ray and a wavefront?

Answer 32

always a right angle

Question 33

What do most objects have?

Answer 33

diffuse surfaces whihc means light rays are scattered in all directions

Question 34

What is a transparent medium ?

Answer 34

A transparent medium is a medium which transmits all wavelengths in the visible spectrum without reflecting or absorbing any.
-Air and water are the most common transparent media