Light and Optics Lecture

What color is white light?

What color is a blue sweater?

Essentially, what do glasses/contacts do?

If you were to throw a rock at an object in a pool or stream, where would you have to aim in order to hit it?

1. Electromagnetic spectrum

A. when electrons move there are two waves of energy are created: electric and magnetic waves:

called the electromagnetic spectrum: they are perpendicular to each other:

B. the energy released is a continuum of varied wave frequencies traveling at the same speed:

-low energy long wave radio waves

-through medium wave visible light (one millionth of 1% of the spectrum!)

-to high energy short wave gamma waves

2. Light

A. origins

1. light is energy carried as oscillations in the electromagnetic waves: move a magnet at 100 million times a second (450 million/sec = red light)

2. when energy is transmitted into matter, the electrons of the atoms vibrate, causing instability and thus photon release

3. one way to energize matter is to heat it: releases incandescent light:

-low efficiency due to excess heat by-product

fluorescencent light: release u.v. waves

4. the color released depends upon 1) which shell the electrons originated and its photon of light released when falling back to its stable shell:

and 2) the natural frequency of the type of matter being energized

B. What is light

1. pure energy, carries information

- travels as a wave: high frequency (short wave length)

and as a photon (bundle of energy)

-energy for white light depends on the color: roygbiv:

red: lower frequency 462THz (energy) than violet: 750THz (high frequency, energy)

2. fast: 300,000 km per second (186,000 mi/s)

- million times faster than sound:

see bat hit a ball before you hear the crack of the bat

lightning before thunder

3. travels in both straight lines and can be bounced (reflected) and bent

4. has different intensities and colors:

roygbiv:

5. the wavelength of light is extremely small, measured on the nano scale (?).

thus light has a very high wave frequency

this high frequency means light has huge amount of energy (related!!):

red = low frequency/low energy

yellow = medium frequency/medium energy

violet = high frequency/high energy

3. Color

A. Eye (human)

1. has two different photoreceptors (cells)

- cones

- rods

2. rods

- detects light intensity: white-grey-black

- used for night vision, where cones cells do not function

- 20x more cells ( 130 million) than cones,

thus black/white vision is more sharp than color vision

3. cone cells

- detect color

- three types of rod cell:

detect red: low frequency

detect green: medium freq.

detect blue: high freq.

- thus the eye does not see the entire roygbiv spectrum of colors

B. different colors

1. because the eye detects only the red, green and blue spectrums,

it must use these to create all the other colors of the spectrum: additive process

the eye uses additive colors to make colors it cannot directly detect:

-yellow

-magenta

-cyan

2. observing colors

- colors are due to light bouncing off (reflecting) the viewed object:

- pigments in viewed objects work by removing/absorbing colors from white light (subtractive):

pigments in green leaves (chlorophyll) absorb all the colors of roygbiv except green

these pigments then reflect the unused green light back to your eye:

thus, leaves do not use green wavelength of energy to make carbohydrates/sugars

4. Optics

- the science and technology (lenses) of light

A. light interacts w/ its environment in four ways:

1. light does not travel through the object, but its energy is absorbed by the object

2. the object is transparent: travels unchanged through the medium: windshield

3. the object is translucent: light travels through but is scattered: frosted glass

4. light is reflected: bounced off the medium: mirror

B. light movement

1. as light travels, it always travels in a straight line while in the same medium.

It is when light changes mediums or surfaces that it is bounced (reflected) or bent (refracted)

2. reflected light:

- light is bounced off the surface of the medium

- incoming light ray is called the incident ray and

the outgoing light ray is called the reflected ray

3. the angle of the incident ray is equal to the angle of the reflected ray, relative to the normal line

4. normal line is the imaginary line which lies perpendicular to the medium’s surface

5. refraction

- the bending of light, due to light passing through a new medium: air into water

- bending is due to the speed of light being slowed down by traveling through something

- not all light waves slow down equally: called the index of refraction: the degree to which the light

waves are bent

air 1.00 I.R.

water 1.33 I.R.

glass 1.50 I.R.

diamond 2.42 I.R.

- the amount the light wave bends toward the normal line is called the angle of refraction

C. lenses

1. transparent material (glass/plastic) which has a curved surface,

such that incident light rays are bent in a specific direction

by both entering the lens (refracting) and exiting the lens (refracting a second time)

2. there are two major categories of lenses: divergent and convergent:

a. convergent lens

- light exiting the lens comes together at a specific point (focal point)

-focal length is the distance from the lens to the focal point

- lens surface is convex:

curves out

- examples of your eye’s lens:

- human eye w/ incorrect focal length and w/ corrected focal length due to glasses:

b. divergent lens

- light exiting a lens spread out (bend) away from the focal point

- lens surface is concave (caves curve in)