physics - optics- unit test (3.9-3.19) Flashcards
what is the gaussian equation
1/f = 1/d(of object) + 1/d(of image)
what is the gaussian equation used to find?
relationship b/w focal length, object distance, and image distance
define optical density
amount of light that passes through an object (ex. low optical density = more transparent, high optical density = more opaque)
what is refraction
the bending of light as it travels between 2 different mediums with different optical densities
why does refraction occur
the more optically dense a medium is, the slower light moves and vice versa, as light changes speed it”bends”
what happens when light has an incident angle of 0 during refraction?
nothing, the light passes straight through without bending
light bends closer to the normal when..
it goes from a less dense medium to a more dense medium (light slows down)
light bends further from the normal when..
it goes from a more dense medium to a less dense medium (light speeds up)
what is the speed of light in a vacuum?
3.00 x 10^8 m/s
why does light slow down in mediums? (when going from vacuum to medium)
the particles that make up the medium slows down light
what does the index of refraction show?
the comparison between the speed of light in a vacuum and a material (medium)
the more optically dense a medium is the ____ light travels and the ______ index of refraction
slower, higher
what is the index of refraction of light traveling through a vacuum?
1.00
how can the index of refraction be found?
index of refraction (n) = speed of light in vacuum (c)/speed of light in medium(v) OR n = real depth/apparent depth
light will ____ as it goes from air to water and refract _____ to the normal
slow down, towards
light will ________ as it goes from air to oil and refract __________ to the normal
slow down, towards
in which medium does light refract more, oil or water?
oil
what is snell’s law?
n1sinθi = n2sinθR
- n1 = index of refraction of first medium
- n2 = index of refraction of second medium
- θi = angle of incidence
- θR = angle of refraction
how can a graph be used to find the index of refraction or a medium?
index of refraction = rise(sinθi)/run(sinθR)
what should be remembered when graphing refraction?
- clear descriptive title
- logical scale
- sinθi is y axis, sinθR is x axis
- plot points, find line of best fit
- label lines (if more than one)
how do refraction in lenses work?
light refracts twice as light enters glass and light leaves glass
- can be drawn as one refraction with the optical axis in the middle of the lens
what do converging lens do?
they focus light rays to the focal point
what do diverging lens do?
they cause rays to move apart from each other but when new rays are extended behind lens, they meet at another focal point
what is the principal axis, where is it found?
imaginary horizontal line that goes through the middle of the lens
what is the optical axis, where is it found?
the imaginary vertical line that goes through the middle of the lens (used to simplify refraction)
what is the vertex?
where principal axis and optical axis meet
what are the primary and secondary focal points? (F’ and F)
the point where parallel rays of light converge or diverge from
what is the focal length?
distance b/w focal point and vertex
what are the three ways to find an image in converging lens?
- parallel incident ray which bends and principal axis (PA) to go through focal point
- incident rays which goes through focal point and bends to become parallel to PA
- incident ray that passes straight through the vertex
why can you see both outside and your reflection while looking out a window?
some light reflects back while some refract and allows you to see outside
- this doesn’t happen equally and depends on the angle of incidence
what does TIR stand for?
total internal reflection
what is TIR (total internal reflection)
when the incident ray passes the critical angle and all the light is refracted/reflected in medium#1
define critical angle
the angle of incidence when the angle of refraction is 90 degrees
when does TIR occur
- ONLY when light travels from a medium of higher optical density to one with a lower optical density
- when incidence ray passes critical angle
what is the relationship b/w the incidence ray and reflection/refraction when going from more dense–>less dense?
- larger the incidence ray, the more reflection and less refraction
- the smaller the incidence ray, the more refraction and less reflection
why do stars appear to twinkle?
light refracts (and slows down) as it enters the earth’s atmosphere from space (a vacuum)
why do things appear to shimmer during hot days?
light refracts through warm/hot air
how is TIR seen in diamonds?
- as light tries to go from diamond to air, the incident angle is sometimes larger than the critical angle which allows TIR to occur and the light gets “trapped” in the diamond
- sometimes rainbows can be seen exiting from diamonds, this is the diamond refracting the colours which have different densities and cause different refracted angles
how is TIR applied to fibre optic cables?
- light hits boundary of cables at an angle larger than the critical angle which causes it to reflect (tir)
- as this happens multiple times, it moves light through the cables
how does TIR create rainbows?
- light refracts as it enters the raindrop(dispersion of colours), reflects off back of raindrop (tir) and refracts again as it leaves the raindrop allowing all colours to be seen
why do mirages occur?
different air temperatures cause light the refract at different angles
how do inferior mirages work?
- cold air is denser than warm air so when light goes from colder air to warmer air, the light rays bend upwards
- our brain then automatically extends the refracted ray to the ground which is why images are seen on the ground
how to superiour mirages work?
- since warm is is less dense than cold air, when light goes from warm air to cold air the light rays bend down
- our brain automatically extends the refracted ray which results in the image being projected in the sky
how is TIR seen in prisms
prisms can create the right conditions for TIR since the critical angle b/w glass and air is 45 degrees
- any incident angle larger than 45 degrees creates TIR
how is TIR used in periscopes
they use triangular prisms to change the direction of light by 90 degrees
how is TIR used in binoculars
2 pairs of triangular prisms are used the change the direction of light by 180 degrees each
characteristics of CONCAVE MIRRORS
- they converge light rays
- the real image is on the same side as object
- virtual image is produced when object is b/w F and V
- positive height when object is b/w F and V
characteristics of CONVEX MIRRORS
- they diverge light rays
- the real image is on the same side as object
- virtual image is always produced
- there’s always a positive height
characteristics of CONCAVE LENS
- they diverge light rays
- the real image is on the opposite side of object
- virtual image when object is b/w F and V
- positive height when object is b/w F and V
characteristics of CONVEX LENS
- they converge light rays
- the real image is on the opposite side of object
what is the cornea
transparent part of eye that refracts light
how do the iris and pupil work together?
iris (coloured part) controls amount of light that enters through pupil (dark circle)
what are the lens in eyes? what do they do?
- transparent convex structure that refracts light onto retina to create an inverted image
what is accommodation?
the ability for lens in eyes to change shape to focus on objects at different distances from the eye
what is the closest focusable distance called? around when does it reach 30cm?
the near point, around age 40
what do fluids in the eye do?
help maintain shape and pressure of eye
what is the aqueous humor? where is it located?
- located in the front of the eye (in front of lens)
- a fluid that brings oxygen to eye, removes waste products, and protects eye against UV radiation
what is vitreous humor? where is it located?
- located in the back of the eye (behind lens)
- gel-like a fluid containing collagen, water, and hyaluronic acid
what are floaters? why do we see them?
- specks, strands, cobwebs, rings that are visible through eye
- as humours break down floaters can become visible
- debris can cast a shadow on the retina
what is the macula and its functions
- part of retina that allows us to see 20/20 and gives colour to our vision
what is the fovea? its functions?
- small pin sized part located in macula
- the fovea is the centre of view and gives the sharpest images (contains almost all cone cells)
how are we able to see colour?
3 different cone cells (red, green, blue) all have different pigment which absorbs light at different energies allowing us to see colour
- cone cells don’t work in low light so we cant see colour in the dark
why does colour blindness occur?
- when one or more types of cone cells aren’t functioning
- usually genetic disorder inherited from mother
are men or women more likely to be colour blind? why?
- men since they only inherit one X chromosome while women get two
- if the one X chromosome has the colour blind mutation, males will be colourblind, but since females have two X chromosomes if one has the mutation, the unaffected X chromosome will take over
what are rod cells? about how many are in each eye?
- rod cells allow us to see light intensity and are the reason we can see at night
- about 90 million in each eye
what is the blind spot? why don’t we notice it?
- the optic disc where optic nerves meet and exits eye
- no light sensitive cells on optic disc
- our brain automatically fills in the gap
what allows someone to have normal vision
- when eye/cornea/lens are the correct shape
- when light focuses on retina and form an image
what is myopia
- when close objects are clear but far objects are blurry (nearsightedness)
- occurs when light refracts too much in cornea/lens and creates image in front of retina
what can cause myopia?
- eyeball is too long
- cornea is too curved
- lens is too thick
what glasses are needed for myopia? why?
- glasses are made of diverging lens (concave)
- diverging lens force light to diverge a bit before refracting through the lens to retina allowing image to be formed at the retina
what is hyperopia?
- when far objects are clear and objects closer are blurry (farsightedness)
- occurs when light rays aren’t refracted enough in cornea/lens and creates an image behind the retina
what can cause hyperopia?
- eyeball is too short
- cornea isn’t curved enough
- lens is too thin/flat
what glasses are needed for hyperopia? why?
- glasses are made of converging lens (convex)
- converges light rays before they’re refracted through the lens which allows light to converge at the retina and create an image
how are contact lenses different for myopia and hyperopia?
myopia: lenses are thicker on the edges and thinner in the middle
hyperopia: lenses are thinner on the edges and thicker in the middle
what is laser surgery, how does it work?
a laser is used to remove tiny pieces of the cornea and reshapes the curvature to allow light to refract correctly into the retina
