Optics
Chapter 4: Many properties of light can be understood using a wave model of
light.
S
The History of Light
S Pythagoras
S A Greek philosopher
S Believed that beams of light were made of
tiny particles.
S The eyes detected these particles and could
see the object.
Galileo
S Galileo is believed to be the first person to try and measure
the speed of light.
S He and an assistant stood on hilltops about one kilometer
apart holding lanterns.
S He would uncover his lantern first and as soon as his assistant
saw the light he would uncover his lantern.
S Galileo would then measure the time between the moment
that he saw the light from his assistants lantern.
S He was unable to calculate the speed of light from his results.
Albert Michelson
S First person to measure the speed of light
(3 x 108 m/s)
Speed: Light vs. Sound
S Light
S Sound
1 000 000 000 km/h
1 200 km/h
Thunder and Lightning
S Both the lightning strike and the roar of
thunder happen at the same time.
S You see the lightning first.
S If you multiply the time in seconds
between the strike and the roar by the
speed of sound, you will find the
approximate distance.
Orion’s Belt
S The light takes thousands of years to reach our
eyes.
Light Technologies Include…
S Microscope
S Telescope
S Periscope
S Binoculars
S Fibre Optics
S Camera
S Prescription contact lenses
S Laser
S Movie Projectors
S Overhead Projectors
Properties of Waves
S A wave transfers energy through matter or
space.
The Wave Model
S Explains that light is a type of wave that
travels through empty space and transfers
energy from one place to another.
A Wave…
1. Wavelength
3. Crest
2. Amplitude
4. Trough
•
A Peak is also called the crest and is the highest part of the
wave.
•
Trough = the lowest point in the wave.
Frequency
S Frequency: the number of repetitive motions that occur during
a given time.
S Ex: the number of wavelengths that pass a point in 1 second.
S Measured in Hertz
Amplitude
S Amplitude: the height of a wave crest or the depth of a
wave trough as measured from rest position.
S Crest height = trough depth
S The larger the amplitude the greater the energy transported.
Wavelength
S Wavelength: the distance from crest to crest, trough to
trough or the distance covered by one complete crest and
one complete trough.
S Measured in: meters.
S Longer wavelengths refract the least.
Frequency & Wavelength
S High frequency waves have short wavelengths.
S Low Frequency waves have long wavelengths.
Transverse Wave
S Transverse Wave: matter in the medium moves up and
down perpendicular to the direction that the wave travels.
S Example: When you shake one end of a rope while your
friend holds the other end.
S The wave travels from you to your friend.
S The rope moves up and down.
Compression Wave
S Compression Wave: matter in medium moves back and
forth along the same direction that the wave travels.
S Example: Squeeze several coils of a spring together at one
end of the spring. Then let go of coils (while still holding
onto the end). A wave will move along the spring.
Waves
Light
S Light: a form of energy that can be detected by
the human eye.
S Visible Light: a mixture of all the colors of the
rainbow.
Properties of Visible Light
1: Light Travels in a straight line.
S (rectilinear propagation)
2: Light Reflects
(reflection)
3: Light refracts. (refraction)
4: Light Disperses
(Dispersion)
5: Light travels through a vacuum (does not require a
medium; no particles involved)
6: Travels through objects at different
degrees.
https://www.youtube.com/wa
tch?v=ldGWaLRIL4Y
http://studyjams.scholastic.co
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rgy-light-sound/light-absorbreflect-refract.htm
Visible Light Spectrum
S Can be seen due to the dispersion of light
through a prism.
The constituent colors of white
light are:
S Red
S Orange
S Yellow
S Green
S Blue
S Indigo
S Violet
ROY G BIV
** Red has the
smallest refraction
and violet the
greatest.
S When a laser is
shone through a
prism, the light
will refract but
NOT disperse.
WHY? A laser light
is only one color.
Refraction
S Refraction: the bending or changing direction of a wave as
it passes from one material to another.
Spectrum
S The range of colors or frequencies of visible light is called
the visible Spectrum.
Reflection
S Reflection: occurs when a light wave strikes an object and
bounces off.
S When sunlight hits a colored clothing some colors are
reflected and others are absorbed.
Electromagnetic Radiation
S The transmission of energy in the form of waves that extend
from the longest radio waves to the shortest gamma waves.
http://www.watchknowlearn.org/Video.asp
x?VideoID=30186&CategoryID=8281
Types of Electromagnetic
Radiation
S 1. Radio Waves: the longest wavelength and lowest energy
and frequency.
S Can be used to help us see the inside of our bodies to
diagnose illness. Ex: MRI
Magnetic Resonance Imaging
2. Microwaves: have the shortest wavelength and the
highest frequency of all radio waves.
Ex: Microwave ovens, telecommunication satellites,
radio telescopes, radar (remote sensing).
Microwave ovens use a specific frequency that is strongly absorbed by water
molecules in food.
S 3. Infrared Waves: longer wavelength and lower energy and
frequency.
S Infrared means below red.
S Also called heat radiation.
S Ex: Remote controls, computer, heat lamps, motion sensors.
S 4. Visible Light Spectrum: can be continually
detected by our eyes.
S 5. Ultraviolet Waves: shorter wavelength and
higher energy and frequency.
S Very Energetic
S Have the ability to kill bacteria in food and
water and medical supplies.
S Ex: Sun, detect fingerprints.
S 6. X-Rays: have a shorter wavelength, and
higher energy and frequency than UV.
S Used to photograph teeth, bones and the inside
of machines, security screening.
S 7. Gamma Rays: have the highest energy and
frequency and the shortest wavelength.
S Result from nuclear reactions.
S Produced by the hottest regions of the
universe.
Gamma Rays: Nuclear Explosion
Gamma Rays: Medical Treatment
Electromagnetic Radiation… A
Safety Concern
S Generally, higher energy electromagnetic radiation is more
harmful to humans.
S The Earth`s atmosphere is able to protect us from some of
the more dangerous electromagnetic radiation present in
space, making the Earth a safe place for humans.
S Changes to present conditions may comprise our safety.
S https://www.youtube.com/watch?v=jjy-
eqWM38g&list=PL8dPuuaLjXtPAJr1ysd5yGIyiSFuh0mIL
&index=24