Optics Flashcards
What is refraction
the bending or changing of the direction of light when it travels from one medium to another
Light travels at different
speeds in different materials
Speed of light in a vacuum
3.00 * 10 ^8 m/s
Speed of light in water
2.25*10^8 m/s
Physicists can measure the
optical density of a material
What is optical density
the ability of a meterial to slow down the movement of light
The higher the optical density the
slower the movement of light and thus the more bent the light appears
Is it possible for light to travel faster than it does in a vacuum
no! in a vaccuum light will move as fast as it can,
Why does light move the fastest in a vaccuum
as there is nothing to slow it down
When light travels from one medium it will
change direction and appear to bend
Thus refraction occurs
as light crosses the boundary between two different materials
When light moves from one medium into another of greater optical density the refracted ray will
bend towards the normal
(slowing down)
When light moves from one medium into another of lower optical density the refracted ray will
bend away from the normal (speeding up
when light moves from water to air it
bends away from the normal
And image in water will appear
closert to the surface than the object
Total internal reflection can occur when
light moves from a medium with greater optical density into a medium with lower optical density
As light refracts some light will
also reflect back and follow the law of reflection
As the angle of incidence increases, the intensity of light gets
weaker in therefracted ray and stronger in the reflected ray.
The critical angle (OC) is the angle of incidence where the refracted ray is
directly on the boundary, 90 degrees to the normal
At an angle of incidence
reater than the critical angle, light does not refract at all, and only reflects back into the initial medium
The principle of total internal reflection is used in many places including
periscopes, binoculars, and retroreflection
Diamonds are cut in specific ways to make use of what
total internal reflection
Total internal reflection makes them sparkle
Fiber optic cables work because of
total internal reflection
Light travels at different
speeds in different mateirials
Physcistits compare the speed of light in a vaccuum to the
speed of light in a particular medium,
The ratio comparing the speed of light in different materials is called
the index of refraction
The speed of light is different for each medium but is always
less than the speed of light in a vaccuum
You can determine the index of refraction (n) by doing what
dividing (C) speed of light by (v) speed of light in your materials
C and v are both speeds which means that n will have no
units, it is a dimensionless quantity
Where have you seen or used lenses
glasses, contacts, magnifying lenses, microscopes, telescopes, camera
The eye also contains a lens which allows you to focus on objects
near and far
Leses consist of two basic shapes
convex - converging
concave-diverging
Convex lenses are thickes in the
middle
lens CONVEX-light rays that are parrallel to the PA will
converge through a single point after they have been refracted
CONVEX-The thicker the lens
the smaller the focal legnth
Concave lenses are thinnes in the
middle
CONCAVE-light rays that are parrallel to the principal axis will
diverge as if they had come from a single point
CONCAVE-The thicker the lens
the smaller the focal legnth
There are always two
points of refraction in a lens
The first point of refraction is
at the boundary between the air and glass
the second point of refraction is
between the glass and the air
we will simplify our diagrams by adding a
central line and only showingg light refracting once
CONVEX: primary focus
light rays parrallell to the principal axis meet being refracted (F)
CONVEX: secondary focus
located on the same side as the incident rays F’
CONVEX: Twice the focal legnth is
2F 2F’
CONVEX: Optical center is
(O) the middle of the lens and the point at which the principal axis meets the lens
CONVEX: an incident ray that goes through F’ will
refract parrallell to the principal axis
CONVEX: an incident ray that goes through O will
continue on the same path
CONVEX: an incident ray parrallell to PA will
refract through FA
CONVEX: An incident ray passing through 2F’ will
refract through 2F
CONCAVE: what switches for concave lenses
F and F’
F is now on the incident side
CONCAVE: An incident ray parrallel to the PA that meet the lens will
refract as if it came from the focal
CONCAVE: an incident ray moving towayrds F’ will
refract parrallell to PA
CONCAVE: an incident ray that goes through O will
Continue
LEns CONVEX: beyond 2F (SALT)
Smaller, Inverted, Between F and 2F, Real
CONVEX: at 2F (SALT)
Same, Inverted, On 2F, real
lens CONVEX: Between F and 2F
Larger, Inverted, Farther than 2F, Real
CONVEX: At F
NO IMAGE
CONVEX: Between F and O
Larger, Upright, Between F and lens, Virtual
CONCAVE: Beyond 2F
Smaller, Upright, Between F and the lens, virtual
CONCAVE: At 2F
Smaller, Upright, Between F and the lens, virtual
CONCAVE: Between F and O
Smaller, Upright, Between F and lens, Virtual
Equation to find the focal legnth
1/F (focal legnth) =
1/di
(distance from mirror lens to image, if negative image is virtual)
+ 1/do (distance from mirror lens to object)
WHat is magnification
the change in image size compared to the object
Give me the equation for M using height of image, and height of object
M (Magnification =
hi/ho
Give me the equation for m using distance of image and distance of object
M= -di/do
give me the equation for M using height of image, heigh of object, distance of image, and distance of object
M=hi/ho=-di/do
If the image height is - the image is
inverted
IF the image size is greater than the object the magnification will be
greater than 1
IF the image size is smaller than the object the magnification will be
less than 1
Where is the optical nerve
behind the ey
What is the cornea
the very outer part of the front curve (looks like a contact)
What does the lens look like
a circle in the eye (inside)
What does the pupil look like
air bubble above the lens
The sclera is
the outer part of the rest of the eye
Choroid is
the first ring below the sclera
The retina is
the second ring below the sclera
the fovea is
the bumpy part at the back
The iris iss
the little bumps in the pupil
The ciliary body is
the part of the eye inside the sclera that doesn’t have a retina or choroid
The entire eye is a focusing system that involves
the cornea, the lens, the retina
Good eyesight requires
precise focusing of light rays onto the retina
The CORNEA
Outer layer of the eye,
made of living celss that are completely clear,
light arriving at the cornea is refracted through the pupil
THE LENS
the lens is convex
The focal legnth can be adjusted to meet different needs
The lens is attached to cilary body, which can contract or relax to alter the shape of the lens
When muscles in teh they eye contract the lens becomes
more spherical and thicker, to focus on nearby objects
When muscles in the eye relax the lens becomes
less spherical and thin to focus on distant objects
The RETINA
a layer of light sensitive tissue in the back of the eye
the light has already been focused by the cornea, pupil and lens
The image is formed inverted but the brain interprets the image as rightside up
3 categories of vision issues
Hyperopia (Far sighted)
Myopia (Near sighted)
Astigmatism (unable ot focus light rays)
Hyperopia
can focus on distant image, can’t see nearby
Eye can’t make the lens thick enough to foucs light on the retina, light is not refracted enough
Myopia
can focus on nearby objects and have difficulty focusing on distant objects,
the eye cannot make lens thin enough to focus light rays on the retina the light is refracted too much
Astigmatism
the eye is unable to focus light rays on the retina because of an irregualr shape of the cornea
Where’s MY CAVE oh it’s NEAR WE’RE IN FRONT OF IT
Myopia
Concave
nearsighted
light rays cross infront of the retina
Conduction
thermal energy can be transferred between molecules in direct contact with each other
Heating up a pot or pan and the handles hot or place a spoon in tea and it gets hot is what
Conduction
Materials that aren’t good conductors
WHat are they called
Plastic, wood
Heat can’t travel easily
Insulators
What percent of the energy of sun is reflected back into space and by what
29
by clouds, particles in the atmosphere and the Earth’s surface
what happens to the remaining 71% of energy from the sun
it is absorbed by earth’s surface, clouds and gasses in the atmospher
Earth’ warm surface emits
lower energy infrared radiation back out
The amount of energy radiated by earth’s system is
equal to the amount of energy earth’s system absorbs by the sun
Since these energy amounts are balanced Earth’s global temp stays fairly consistent
Albedo is
the relative amount of the sun’s energy reflected by a surface
Albedo warming
albedo decreases as ice melts-water absorbs more heat-arctic gets warmer-ice melts
Albedo cooling
albedo increases-ice reflects more heat-arctic cools-ice forms
What is a low albedo substance
water
what is a high albedo substance
snow
SOup on stove spoon gets hot, what is this
conduction
Heater warms the pool
convection
warm day bench at park is warm
radiation
bbq you feel hot
radiation
Why can’t conduction and convection occur in space
Heat conduction and convection do not occur in space since there is no air in space. Heat transfers in space, which is a vacuum, only by radiation.
Does warm water rise or fall in cold water
Rise. This is because the warm water is less dense and it floats on the cold water – in the same way that a cork floats because it is less dense than water.
Why doesn’t convection occur in solids
Convection is not possible in solids because for convection to take place the molecules of a substance should be free to move like liquids and gases. The molecules of a solid are tightly packed together, thus making it difficult for molecules to move around for convection to take place.
We can see our surroundings because
light bounces off of objects and into our eyes
the electromagnetic spectrum is made up of
different sized wavelegnth
Humans or only able to the see the
visible portion of the EM spectrum
The shortest wavelegnths are, the longest are
gamma waves, radio waves
all of the different wavelengnths combine together to
form a continuous spectrum
what is our most abundant light source
the sun
How does the sun make light
when energetic hydrogen atoms at the center of the sun collide they sometimes combine or fuse to form helium. These reactions are called fusion reactions. SOme of the energy produced by fusion is emitted as light
white light
most sources emit white light. White light is a combination of all wavelegnths of light. When light passes through a prism it is dividied into specific wavelegnths (colours)
rods
sensitive to dark changes shape and movement they are not effective at deticting colour
cones
used for colour vision and are wavelegnth specific
red cones
detecets long wavelegnths (red, orange, yellow)
green cones
detects medium wavelegnths, (yellow, green, blue)
blue cones
detects short wavelegnths (blue vilet)
when is a person colourblind
when one or more types of their cones are partially or completely defficient
dog vision
dogs have 2 types of cones (can’t see red, orange and some yellow)
bee and butterfly vision
better vision able to see colours that we can’t, can see in to the ultraviolet region
Incandescence
energy in-energy out (light. Something gets really hot and releases energy as light.
Examples: heating up a strucutre and it glows red. Incandescent light bulb filaments get really hot and glow bright white
electric discharge
electric current through a gas. the gas releases the energy as light.
Examples: neon signs, lighting
phosphorescence
materirals absorb UV energy and release the energy over a long period of time.
Example: Glow in the dark
fluorescence
materirals absorb UV energy and release the energy immediately as visible light.
Example: Fluorescent bulb, comact fluorescent bulb, detergents
chimluminescence
light from chemical reaction , example: glowsticks, luminol
bioluminescence
light produced by chemical reactions within living things.
Examples: jellyfish, algae, fireflies, angler fish
triboluminescence
light produced from hitting or sticking rocks or crystales (friction)
example: flint, flint lighters
LED (light emitting diodes)
electricity passes through specific materials (semiconductors like silicon or galium), that release particular wavelegths of light
Examples: phone screens, computer screens, TVs, anything with red, green blue
light travels in
straight lines
lights straight lines are represented by
rays which show direction that light travels after it leaves its source
rays
each ray ends with an arrow, to indicate the direction of travel. IF more rays reach your eye the brighter the object appears
rays leaving the source
travelling toward an object travel closely to one another
the science of how light reflects and bends is called
geometric optics
angle of incidence =
angle of relflection
images are formed in the location wher
the relfelcted light rays cross. Therefore when your eyes detereflected light from a plane mirror, your brain projects these light rays backwards in a straight line. Your brain perceives a light source behind the mirror and that this source is where the light rays originate. this type of image is called a virtual image
a virual image is
an image formed by light coming from an apparent light source behind the mirror. the reflected light rays from a plane mirror will nvever cross in front of the mirror. However if the reflected light rays are extended behind the mirror the rays will appear to cross. this is where the image is found
SALT
Size of Image: comparison to object
Altitude of Image: image orientation compared to object
Location of image: point where reflected rays cross or appear to cross, how far from the mirror the image is compared to object
Type of Image: a real image or virtual
two characteristics of plane mirrors
virtual images, angile i= angle r
angle of incidence
angle where ray hits mirror
angle of reflection
angle leaving mirror
incident ray
ray of light going towards mirror
normal
perpendicualr line from mirror
reflected ray
light ray reflected from mirror
Curved mirror
depending on whether the reflective coating is on the inside or outside of the curve will decide if its a concave or convex mirror.
If coated on inside its concave
if coated on outside convex
circle terminology for mirrors
a curved mirror is a cut out section of a circle. IN mah the distance from the curve to the centre of the circle is referred as the radius. for the purpose of mirrors this called the center of urvature
principal axis
a line through the cneter of the of curvature that strikes the mirror at a 90 degree angle
vertex
point of a curve mirror wher PA meets mirror
the center of curvature and vertex are on
the principal axis
half of the distance between the centre of curvature and mirros is
focus or focal point. this is why focus is F and center of curvature is 2F
Concave: when incident ray goes through the center of curvature the reflected ray will
reflect back on itself
Concave: incident ray parallel to pa will
reflect through focal point
Concave: incident ray passing through focus will
reflect parallel to PA
Convex: Parallele to Pa
reflect from focal
convex: passing through focus
reflect Parallelt to PA
convex: trhough center of curvature
back on itself
concave beyond C
smaller, upside down, closer, real
concave at c
similar size, upside down, at c real
concave vetween f and c
larger, upside down, on c, real
concave at f
wont reflect
concave between f and the mirror
larger upright further virtual
convex far from mirror
smaller, right side up, closer (f and mirror), virtual
convex closer to mirror
smaller, upright, between mirror and f, virtual
convex closest to mirror
smaller upright, between mirror and f, virtual
