Waves and Light Exam

How do we see?

With our eyes and brain

Parts of the eye

cornea, pupil, iris, lens, retina, optical nerve

Cornea

clear transparent dome-shaped window covering the eye, light is bent by the cornea as it enters the eye

Iris

colored part of the eye

Pupil

opening center of the iris

\-controls the amount of light entering the eye

\-small amounts of light will cause the opening to increase \n -its size will also change due to emotions

Lens

finishes bending the light so that it falls on the back of the retina of the eye. Near or farsightedness means the light is not focused on the retina

\-It is a convex lens and therefore. Converging \n -The image that falls on the retina is an inverted (real) image of what you are looking at

What are the two types of retina?

rods and cones

Rods

Give your movement to help your side vision.

Centered towards the edges.

Lets you see black and white.

Cones

color vision

Optical Nerve

transmits the electrical energy or signals to your brain

\-your brain "reads" signals and turns them into images

Light

a beam of electromagnetic radiation traveling in a transverse wave

electromagnetic spectrum

the continuum of light that travels at the \n speed of light in a vacuum

Light speed

3 x 10^8 meters/second or 186,000 miles/second

The average light speed will \__________ anytime it enters a \______________.

slow down; medium

Wave

a movement of energy

Reflection

bouncing back of waves from hitting a barrier

Refraction

the bending of a wave due to a change in the medium

Diffraction

bending of waves around a barrier

Interference

when one wave crosses another. Energies add (+ or -) when waves cross. It can be constructive (wave builds) or destructive

Doppler Effect

**apparent** change in frequencies of waves due to motion of source, observer or both

Dispersion

spreading out of waves

Polarization

alignment of waves as it enters a material.    

Law of Reflection

The incoming (angle i) angle is equal to the reflected angle (angle r)

Smooth Reflection

parallel in, parallel out

Diffused Reflection

parallel in, not parallel out due to uneven surface

Normal Reflection

line perpendicular to surface at the point where the wave hits the boundary

Doppler Effect Rule: If the object is coming toward you then there is an ______________ in the frequency.

increase

Doppler Effect Rule: If the object is going away from you then there is a _______________ in the frequency of the wave.

decrease

Transverse Waves

moves perpendicular to direction of motion, ex: water and light waves.

Longitudinal Wave

moves parallel to the direction of motion, ex: sound wave

Torsional wave

twisting wave

Node wave movement

point of no movement

Wave frequency and period formula

1/p\=f and 1/f\=p

What is amplitude?

energy in a wave

Speed formulas

v=wavelength x frequency &

v= wavelength/period

Types of materials

transparent, translucent, opaque

Transparent

light completely goes through an object

Translucent

some of the light goes through an object

Opaque

do not allow the waves or light to pass through.

Converging Lenses and Mirrors

brings the light to a point

Diverging lenses and mirrors

spreads out the light

Real images

light energy is really there

Virtual images

light energy only appears to be there

Real image characteristics

•Energy is really there;

•Always inverted relative to object; \n •Can be projected; \n •Can range in size from very small to very large if formed from a Converging Lens/Mirror; \n •Can never form in a Diverging Lens/Mirror.

Virtual Images Characteristics

•Energy only appears to be there;

•Always in the same orientation as the object; \n •Can not be projected; \n •Is always smaller if formed from a Diverging Lens/Mirror; \n •Is always larger if formed from a Converging Lens/Mirror.

Telescopes

•Over the entire EM Spectrum;

•Can be reflecting or refracting (optical telescopes) \n •Maximize the light gathering ability \n •Magnification

Magnification

focal length of objective / focal length of the eyepiece.

Microscopes

•visible and scanning electron

Thermoscans

heat

Doppler radar

motion

seismograph

earthquake waves

ultrasound

high frequency sound

CAT Scans

X-rays

Sound

Sound waves are produced by the vibration of the matter

The more elastic the material is the \___________ the wave is transmitted and the \__________ it moves through the material.

better; faster

Elasticity

the ability of a materials to return to its original state after a force is removed

Humans can hear between \_______ to \________

20 Hz to 20,000 Hz

Below 20 Hz is \___________ while above 20,000 Hz is \______________.

infrasonic; ultrasonic

Parts of the ear

outer ear, middle ear, inner ear

Pigment --\> Subtraction Process

•When all the colors of pigments are mixed together they produce a black color

Light --\> Addition Process

When all the colors of light are mixed together they produce white light.

What type of lens is your eye?

convex

Cornea does most of the _________

bending

Retina= ______ image

real

Farsighted is fixed by a _____ lens

convex

Nearsightedness is fixed by a _______ lens

concave

Order of the electromagnetic spectrum from high energy to low energy:

Gamma, x-ray, ultraviolet, visible. infrared/heat, microwave, radio

Example of a transverse wave

Water

Mechanical Wave

requires a medium to travel on

Electromagnetic Wave

does not require a medium to travel on

Snell’s Law is an example of __________

refraction

•As the wave goes from a more dense to a less dense material, the wave is bent _______ from the normal.

away

As the wave goes from a less dense to a more dense material, the wave is bent _______ the normal.

toward

Transverse wave positions

crest (top) and troughs (bottom)

Longitudinal Wave Positions

compressions and rarefactions

Concave mirrors are like convex lenses because they are both ______--

converging (virtual images are larger)

Concave lens and like convex mirrors because they both

diverge (virtural image will be smaller)

Purpose of outer ear

to collect and funnel sound waves through the ear canal to the middle ear.

Purpose of middle ear

helps amplify the vibrations by concentrating the energy into a smaller area as it passes through the tubes in the next section & perceives the sound waves as differences in pressure or pressure waves.

Purpose of Inner Ear

The ear also helps you keep your balance.  The three semicircular canals in the inner ear are filled with a liquid and are lined with tiny hairs.  As you move so does the liquid in the canals. 

Why is the sky blue?

Because of scattering

Why is the sky bluer the higher up you go?

The further you go into the upper atmosphere the smaller number of molecules.  Therefore, the sky will appear a darker blue/deep violet gradually fading into black.

What color is the Sun as we see it on Earth?  Is that the same color the astronauts see from the International Space Station? 

The Sun as seen from outside the Earth’s atmosphere appears to be white.

When we see it from the surface of the Earth it appears a whitish-yellow color.

We see that color because that the average of all the colors left after some of the blue/violet colors have been scattered out.

Visible Light – R, O, Y, G, B, V => we see the average which is white. 

What is a green flash and how is it formed? 

·The atmosphere acts as a prism and refracts the light of the Sun as it is going down. 

· The setting Sun’s light is broken down into its component colors.  Because of the high speed of the Sun however, we usually only see “one” setting Sun.

·If the atmosphere is very clear and very still then it is possible to see a Green Flash and a Violet Flash.

Venus’ Belt

A pinkish brown bad that appears to be resting on the blue sky at dusk/dawn is formed when light from the sun id back-scattered through the atmosphere.

The Glory

The Glory is basically a rainbow seen from above the bow looking down. Therefore, the entire circle of the rainbow is seen.

Why is the sky bluer after a storm?

· After a storm almost everything has been “washed” out of the sky therefore the sky looks bluer after a storm.

·Humidity can also influence how blue the sky appears – the more water in the atmosphere the lighter the blue of the sky.  The drier the atmosphere the deeper the blue. 

How is a halo around the Moon/Sun formed

A halo around the Moon or Sun is caused by the refraction of light through the ice crystals in cirrus clouds

What does a halo usually forecast and what conditions are needed for it to be seen?

·Usually there is no color associated with the Moon because it isn’t bright enough for the light to stimulate the cones in your eye.

\*There is usually some color with the halos around the Sun

What determines the color of a star?

Its surface temperature; red stars are the coolest and blue/white stars are the hottest

Why can’t you see stars during the day on Earth but the astronauts can when they are in orbit? 

·       You can’t see the stars during the day because the Sun is too bright.

·       You can see the stars during the day on the ISS because there is no atmosphere to diffuse the light.

How does the moon shine

It shines because of the sunlight being reflected off of their surfaces. Most materials reflect light as opposed to emitting light.

Why does the Sun/Moon appear to be highly colored when it is rising or setting? What happens to the color as they continue to rise?  Same question as to size – why do they seem so much bigger when you see them rise or set? 

The greater the amount of atmosphere the light goes through, the greater the scattering.

·       Very little atmosphere => white. 

·       Lots of atmosphere => red.

·       The greater the motion of the atmosphere, the greater the scattering as well.

Earthquake Lights

·       Disruption of the Earth's magnetic field by tectonic stress;

·       -Quartz-bearing rocks produce voltages when compressed in a certain way;

·       -Grinding rock can cause stress deep in the earths crust which in some types of rock can break apart pairs of negatively-charged oxygen atoms.

·       May appear before, after or during an Earthquake.

·       Can be similarly shaped like an aurora.

·       Usually have a white to bluish hue but may have a wide color spectrum.

·       Can last anywhere from a few seconds up to 10 minutes.

·       Most commonly occur when quakes have a higher magnitude.

Light Pillars

·       formed from reflection off the ice crystals high in the atmosphere.

·       Usually are only seen in the higher/lower latitudes under certain atmospheric conditions => up north or down south.

·       They show their own color therefore, the light is not refracted.

 

Fire Rainbows

·       formed when light enters a horizontally-oriented ice crystals that is flat and hexagonal.

·       It forms a large diameter arch of which we only see a small portion.  Therefore, the Fire Rainbows look very flat and very colorful.

·       They can only be seen during certain times of the year (usually summer) and from newly-formed clouds.

·       They tend to be seen at latitudes greater than 58 degrees.

Flourescence

·       requires the excited electron to decay and in doing so gives off UV light.  When the original source is turned off the light goes out.  No afterglow.

Phosphorescence

·       Phosphorescence is the same type of process only the decay step is really two steps with the first taking some time.  Therefore, there is a delay in the light seen.  In this case there is an afterglow. 

A cuttlefish (plus other ocean creatures) can change their color to reflect the background they are on.  How does it do this?

·       Cuttlefish and other creatures that change their color to match their environment have multiple layers of chromatophores on their skin.

·       When the chromatophores are activated various colors and textures “mix” together causing the skin to change.

·       There may also be sensors on the skin which automatically pick up information from the environment.  

Color of fur on a polar bear

·       The fur on a polar bear is a thin tube that is transparent and hollow => it acts like a fiber optics tube. 

·       Light from the Sun is conducted down the tube to the skin which is black. Since black absorbs energy very well the bear stays warm.