A form of radiation called electromagnetic because it is
associated with changing electric and magnetic fields When light
enters our eye, the energy stimulates nerve endings and we see what
we call light.
Slide 3
Light acts as both a wave & a particle A particle of light
is called a photon Light can be referred to as a bundle of
waves
Slide 4
2 kinds of light sources: Luminous sources : actually produce
the light they give off EX: sun, other stars, lamps, fireflies
Non-luminous sources : can be seen only after light reflects off of
them EX: moon & people
Slide 5
1.A fuel such as gasoline or wood is ignited 2.The chemical
potential energy stored in the molecules of fuels is converted as
burning occurs 3.Usually both light energy and heat energy are
given off
Slide 6
When metals give off light as a result of being heated EX: a
welding torch at a temperature of 800 C EX: steel is heated to 2500
C
Slide 7
1.An ordinary incandescent light bulb converts electrical
energy to light energy 2.An electric current is passed through a
fine wire filament made of the metal Tungsten 3.As the electrons
move, some of the energy is changed to heat 4.Heat warms the
filament to incandescence and light energy is given off
Slide 8
1.Fluorescent lights contain a tube with an electrode at each
end 2.Electrons bounce around in the tube and collide with Mercury
atoms 3.The collisions cause UV-radiation to be formed 4.The
radiation strikes the fluorescent coating on the inside of the tube
and light is given off
Slide 9
Tungsten metal is used because of its high melting point of
3400 C Incandescent lamps are energy wasters, only about 5% of the
electrical energy used is turned to light Fluorescent lights change
20% of the energy to light Fluorescent lights contain mercury which
is a hazard if you break them inside a house.
Slide 10
Nuclear reactions can cause light energy Nuclear fission and
fusion reactions use the potential energy contained in atoms This
is converted to both heat and light
Slide 11
EX: A Neon Sign Energy can cause an electron of an atom to jump
to a higher energy level When it falls back down, it releases a
photon of light
Slide 12
The Law of Conservation of Energy states yes! EX: Solar Cells
on satellites circling Earth change light energy to electrical
energy EX: Camera exposure meters turn light energy to electrical
energy
Slide 13
Radiation coming from the sun is called Electromagnetic because
it is associated with changing electric and magnetic fields that
travel through space, transferring energy from one place to another
Electromagnetic radiation moves through space at 300,000 km/sec
(186,000 miles/sec) or 3.0 X 10 8 m/sec
Slide 14
Slide 15
By: Brews Ohare
Slide 16
A periodic repeating disturbance = a wave Measuring successive
wave peaks = wavelength Greek letter for Wavelength is lambda
Slide 17
Light also acts as a particle called a photon A photon is like
a packet of light energy When light energy strikes a photo electric
cell, it behaves like a stream of particles carrying specific
amounts of energy The amount of energy depends on its
wavelength
Slide 18
Shorter wavelengths have more energy! h= Plancks constant =
6.6262 X 10 -20 Joule/sec c = speed of light = 3.0 X 10 8 m/sec
lambda = wavelength in meters
Slide 19
Slide 20
A spectrum is an array of electromagnetic radiation in order of
wavelength Just as we sense the wavelength of sound as pitch, we
sense the wavelength of light as color Humans can see the visible
light spectrum See the next slide for other examples of the
spectrum
Slide 21
Slide 22
A photometer is used Astronomers use it to analyze
starlight
Slide 23
Unlike sound and other waves, light can travel through a vacuum
Light can travel through some media Transparent media you can see
through like air and glass Translucent media transmits some light
like smoke and frosted glass Opaque media transmits no light such
as wood, black plastic and metal
Slide 24
This is called rectilinear propagation If light travelled in a
curved path, youd be able to see around a corner The path of light
is called a ray A bundle of rays is called a beam
Slide 25
Most objects you can see are non-luminous, that is you can see
them because they reflect light to your eyes Most non-luminous
objects have rough surfaces which reveals their texture and shape
Some non-luminous objects are shiny and smooth and reflect light in
such a way that images are formed = mirrors
Slide 26
Flat = plane mirror The rest are curved mirrors Parabolic
mirrors are specially designed to focus reflected light to a point
in front of the mirror Solar cookers In telescopes by astronomers
Can also focus radio waves
Slide 27
Slide 28
Slide 29
Light may bend as it travels from one medium to the next This
bending is called refraction
Slide 30
Now you will perform some investigations to help you understand
the properties of light. Materials for investigation 1: meter stick
or tape measure, slide projector and graph paper Materials for
investigation 2: Pinhole camera supplies or make one: tissue or
shoe box, wax paper or oiled paper, black electrical tape or duct
tape, aluminum foil, fine pin, candle, matches, rulers,
scissors
Slide 31
Now you will perform some investigations to help you understand
the properties of light. Materials for investigation 3: flashlight,
white wall or paper, equilateral triangle prism Materials for
investigation 4: white cardboard cut to 10-12 cm in diameter,
protractor, markers the color of the rainbow, pencil and pin.
Slide 32
1.Place a slide projector at the back of a completely dark
classroom. Project the beam of light toward the front of the room.
Adjust the lens so it diverges as much as possible. 2.Stand in the
beam of light and face the projector. 3.Use the light meter to
measure light intensity at a distance of 1m from the lens 4.Repeat
step 3 for distances 2m, 3m, 4m and 5m. 5.Record your results in a
data table. 6.Plot a graph with distance on the x-axis & light
intensity on the y-axis.
Slide 33
1.According to your graph, how does distance affect light
intensity? 2.How far do you think light can travel before it can no
longer be seen? (HINT: extrapolate your graph to find the distance
at which the intensity would be zero.)
Slide 34
The pinhole camera is a simple application of the rectilinear
propagation of light. It consists of an opaque box with a pinhole
at one end and a translucent screen at the other end. In this
investigation, you will use the assumption that light travels in
straight lines to predict the nature of the image of a pinhole
camera. 1.Size : is the size of the image larger or smaller than
the object? 2.Attitude : is the image erect or inverted 3.Kind : is
the image real or imaginary (a real image can be caught on screen,
an imaginary image cannot.)
Slide 35
1.Obtain an opaque box such as a shoe box or large tissue box
2.Remove a rectangular section from one end. Replace it with wax
paper or oiled paper. 3.Cut a hole 2-3 cm in diameter at the other
end. Cover this hole with Aluminum foil. Make a pinhole in the
center of the foil with a fine pin. 4.Make sure the rest of the box
doesnt leak light.
Slide 36
1.Put your camera in front of a lighted candle. 2.View the
image on the wax paper. 3.Draw a diagram in your journal showing
the lighted candle and the image on the wax paper. Draw lines to
show how light rays would enter the pinhole camera. 4.Experiment by
moving the camera closer or farther away. 5.Describe in your
journal the size, attitude and kind of image this camera
produces.
Slide 37
1.Compare your predictions regarding the characteristics of the
image with what really happened. 2.Does this investigation support
that light travels in straight lines? 3.What happens to the size of
the image as you move the camera closer to and farther away from
the image?
Slide 38
Slide 39
Slide 40
Shine a light through an equilateral triangle prism so that it
meets one side at an oblique angle. The light should come through
onto a white wall or a white piece of paper. Experiment until you
can see the colors of the rainbow. Record/Sketch your results.
Slide 41
Slide 42
1.From a piece of white cardboard, cut a circular piece that is
10-12 cm in diameter. Draw a diameter through the circle, then use
a protractor to divide the circle into 18 segments of 20 degrees
each. 2.Color the segments in a repeating sequence of red, orange,
yellow, green, blue, violet in a counter clockwise fashion. Repeat
the sequence 3 times. 3.Push a common pin through the center of the
circle and then into an eraser of a pencil 4.Spin the disc rapidly
and observe the effect. If possible, do this in bright
daylight.
Slide 43
This workforce solution was funded by a grant awarded under
Workforce Innovation in Regional Economic Development (WIRED) as
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