Download File - Mrs. Hille`s FunZone

Visible Light and
Its Sources
The Visible Spectrum
• Light is visible at wavelengths
of about 780 nm to 380 nm.
• We see light as colors, not as
waves.
1020
gamma
x-ray
Frequency (Hz)
UV
IR
1010
UHF
RADAR
TV FM
VHF
AM
VLF
101
ELF
Frequency (THz)
700 650 600 550 500
400 450 500
450
550 600 650
Wavelength (nm)
700
400
750
The Visible Spectrum
• Luminous objects produce light.
 Ideally – emits a continuous
spectrum (all possible
wavelengths of visible light)
• The sun comes close to
emitting a continuous
spectrum, but it does have
some gaps.
The Visible Spectrum
• Luminous objects produce light.
 Monochromatic – emits a
single color (a single
wavelength of visible light)
 Other light sources – emit
multiple distinct colors
The Visible Spectrum
• Light projected through a prism
produces a line spectrum.
 line spectrum – distinctly
visible lines of color can be
seen at specific wavelengths
aligned along a scale in a
spectrograph
The Visible Spectrum
 spectroscope – an
instrument designed to
display the line spectrum
 spectrograph – a photo of
the spectrum
Which of the following is a
luminous object?
1.
2.
3.
4.
Light bulb
T-shirt
Piece of paper
Window
Question
The Speed of Light
• depends on the material
through which it travels
• defined as 299,792,458 m/s
(can be rounded to 300 million
m/s)
The Speed of Light
• If 300 million m/s is 18 million
km/min, then sunlight takes
…about 8.3 light-minutes to
reach Earth.
…about 4.2 light-hours to
reach Neptune.
The Speed of Light
• If 300 million m/s is 18 million
km/min, then sunlight takes
…about 4.4 light-years to
reach the nearest star.
…about 100,000 light-years to
travel the diameter of the
Milky Way galaxy.
Intensity of Light
• The intensity, power, or
brightness of a light source is
the rate at which it radiates
energy.
• Intensity is always measured
at the source.
Intensity of Light
• SI unit – candela (cd)
 It is just slightly brighter
than an average candle.
Intensity of Light
• SI unit – candela (cd)
 It is just slightly brighter
than an average candle.
 An ordinary incandescent
bulb makes just less than
1 cd/watt.
 Fluorescent lights emit about
4 cd/watt.
Approximately how many candles
would be needed to give as much
light as a 60 W light bulb?
1.
2.
3.
4.
10
60
95
130
Question
Intensity of Light
• Illumination is the amount of
light received at a distance
from the source.
• The amount of illumination
depends on the brightness of
the light source and the
distance from it.
Intensity of Light
• Illumination and distance from
the light source are related by
the inverse-square law.
 Doubling the distance
reduces the illumination to
one-fourth of the original
illumination.
Intensity of Light
 Tripling the distance reduces
the illumination to one-ninth
of the original.
Distance and its effect on
forces are often related by the
inverse-square law.
1 m2 4 m2 9 m2 16 m2
1m
2m
3m
4m
If the distance is cut in half, the
illumination will be
1.
2.
3.
4.
quadrupled.
doubled.
cut in half.
reduced to one-fourth.
Question
Intensity of Light
• Photometers measure the
illumination of light using a
“solar cell.”
• More light equals more current.
Sources of Light
1. Incandescent
2. Fluorescent
3. Phosphorescent
Incandescent
• Incandescent bulbs have
materials which are heated
until they release visible
energy.
• As the filament gets hotter, the
light goes from red to yellow
and on up the spectrum.
Relative Intensity
4000 K
3000 K
2000 K
0 1000 2000 3000 4000
Wavelength (nm)
Fluorescent
• Fluorescent tubes contain
mercury gas which emits light
as the electricity passes
through it.
• The light is in the UV range.
• Phosphors absorb this light
and reemit it at a lower energy:
the visible light range.
Fluorescent
• A UV lamp is simply a regular
fluorescent tube with little or
no phosphors.
electrode
mercury
low pressure argon
and mercury gas
phosphor
coating
glass
tube
Phosphorescence
• Phosphorescence occurs
when the material continues to
emit light when the source is
removed.
Coherent Light
• Coherent light is “in step” or
“in phase” and of the same
color.
Coherent Light
• Lasers and certain LED (lightemitting diodes) produce
coherent light.
• Since it is in phase, it does not
spread out like ordinary visible
light produced from a
flashlight.
T/F Laser light is
monochromatic.
True
Question
Bioluminescence
• Bioluminescence is light given
off by living creatures like
fireflies.
• It is produced from a chemical
reaction inside the creature.
• Bioluminescence is also called
cold light.
Chemiluminescence
• Chemiluminescence is cold
light produced nonbiologically as in light sticks.
The Nature of
Color
Introduction
• Look at Image 15-14 on p. 361.
• Is the ball red because you
perceive it as red or because
it is red?
• This is a question of
philosophy, not science.
Introduction
Example:
If a tree falls in the forest
and nobody hears it, did it
make a sound?
Introduction
• Scientifically, an object’s color
depends on how your eyes
perceive it.
Color Mixing
• There are two types of color
mixing.
1. Additive (occurs in light)
2. Subtractive (occurs in paint)
Color Mixing
Additive
• Additive means that light is
being emitted.
• The human eye distinguishes
three colors of light. These
colors are called the additive
primary colors or primary hues.
Color Mixing
Additive
• The additive primary colors are
red, green, and blue.
• When mixed they produce the
additive secondary colors:
yellow, magenta, and cyan.
• If all three are mixed equally
they produce white light.
monochromatic
lamps
Color Mixing
Color Mixing
• Color TVs, computer monitors,
and cell phone screens take
advantage of the eye and brain’s
ability to mix colors.
• These screens display only red,
green, and blue, yet the mixture
of colors gives a multitude of
shades of each color.
Color Mixing
Subtractive (Paints)
• Subtractive means that the
colors are reflected.
white light
other
colors
absorbed
green and
some yellow
reflected
Color Mixing
Subtractive (Paints)
• Paints and pigments have three
subtractive primary colors:
cyan, magenta, and yellow.
Color Mixing
Subtractive (Paints)
• Mixing two of the three
subtractive primary colors gives
the subtractive secondary colors
(which are also the additive
primary colors): red, green, and
blue.
Color Mixing
Subtractive (Paints)
• For example, mixing magenta
and cyan paints gives blue paint.
Color Mixing
Subtractive (Paints)
• Mixing all three subtractive
primary colors should give
black.
• Because no pigment absorbs
colors completely, mixing all
three colors often results in
some shade of brown.
Color Perception Systems
1. HSV
Hue
Saturation
Value
H
S
V
Color Perception Systems
2. CMYK
Cyan
Magenta
Yellow
Black
B
M
K
C
G
R
Y
If red, green, and blue lights are
mixed, what color will result?
1.
2.
3.
4.
black
magenta
yellow
white
Question
If red and blue lights are mixed,
what color will result?
1.
2.
3.
4.
cyan
magenta
yellow
white
Question
Reflection &
Mirrors
Light Rays
• A light beam is made up of
many light waves traveling
together in a straight line.
• These waves are represented
by lines called rays.
Types of Reflection
• Diffuse reflection is caused by
rough or uneven surfaces.
Types of Reflection
• Specular reflection is caused
by smooth surfaces.
Reflection Terms
 incident ray – the ray going to
the surface
 reflected ray – the ray
bouncing off the surface
 normal – a line perpendicular
to the surface
Reflection Terms
 angle of incidence – the angle
between the normal and the
incident ray
 angle of reflection – the angle
between the normal and the
reflected ray
Reflection Terms
 Law of Reflection – states that
the angle of incidence equals
the angle of reflection
 This law is true for all rays
and all types of surfaces.
normal line
angle of
incidence
angle of
reflection
incident
ray
point of incidence
reflected
ray
If the incident angle is 40°, what
is the reflected angle?
1.
2.
3.
4.
20°
40°
50°
140°
Question
Plane Mirror Reflection
• A plane mirror is a flat mirror.
• The reflected image appears to
exist an equal distance away on
the opposite side of (behind)
the mirror.
• No actual image exists at this
location (behind the mirror),
so it is called a virtual image.
• The image is reversed left to right.
Curved Mirror Reflection
• A real image is formed from
focused rays that could be
projected onto a screen.
Concave Mirrors
• Concave mirrors are mirrors that
“cave in” on the side exposed to
light rays.
• The light rays must also obey the
law of reflection.
• The light rays converge (meet) at
one point called the principal
focus or focal point.
center
of
mirror
principal optical axis
focal point
Concave Mirrors
• If the object is located further
from the mirror than the focal
point, the image will be real and
inverted.
1
2
object
3
image
2
1
3
focal
point
Concave Mirrors
• If the object is located at the
focal point, no image will result.
Concave Mirrors
• If the object is located closer to
the mirror than the focal point,
the image will be virtual and
upright.
Concave Mirrors
Convex Mirrors
• Convex mirrors reflect light to
produce only virtual images of
varying sizes, but the virtual
images are always smaller than
the original objects.
All mirrors (plane, concave,
or convex) produce images
by reflection only.
Refraction
&
Lenses
Light Refraction
• Refraction is the bending of
light as it passes from one
medium to another medium of
a different optical density.
• Optical density is measured by
comparing the speed of light in
a vacuum to the speed of light
in the material.
Light Refraction
• If light enters a denser material,
the light ray is refracted toward
the normal line.
boundary
surface
angle of
refraction
angle of
incidence
angle of
incidence
angle of
refraction
Light Refraction
• If light enters a denser material,
the light ray is refracted toward
the normal line.
• If light enters a less dense
material, it bends away from the
normal line.
angle of
refraction
angle of
incidence
Light Refraction
• As the angle of incidence of
the light is increased,
eventually the refraction will lie
on the surface of the material.
• This angle is called the critical
angle of incidence.
angle of
refraction = 90°
critical angle
of incidence
Light Refraction
• As the angle of incidence is
increased further, no light is
refracted.
• All the light is reflected back
into the denser material.
• When this occurs it is called
total internal reflection.
totally internally
reflected ray
angle of
incidence
angle of
reflection
Light Refraction
• A fiber optic cable relies on the
total internal reflection to transmit
data and images.
• Endoscopes are tiny cameras
which use fiber optic cables to
transmit light rays.
• The use of endoscopes has
reduced the risk and damage from
exploratory surgery.
Lenses
• With mirrors, light reflects off a
surface.
• With lenses, light refracts
through the material.
• The refracted light either
converges to a point or
diverges (spreads out).
Convex Lenses
• Convex lenses are converging
lenses.
• The light converges to the
focal point which is on the
opposite side of the lens from
the object.
• Many of the terms from mirrors
also apply to lenses.
Convex Lenses
focal point
principal optical axis
focal point
parallel rays
lens
Concave Lenses
• Concave lenses are diverging
lenses.
Concave Lenses
Eyesight Correction
• If a person is nearsighted, the
focal point is in front of the
retina.
• Diverging lenses are used to
correct this.
Eyesight Correction
• If a person is farsighted, the
focal point is behind the retina.
• Converging lenses are used to
correct this.
Normal Vision
Farsighted
Farsighted Corrected
Nearsighted
Nearsighted Corrected
Magnification
• The images produced by lenses
are usually different sizes from
the objects.
• If the image is larger than the
object, the magnification factor
is greater than 1.
Magnification
• If an instrument has several
lenses, the magnification factors
are multiplied together to get the
total magnification.
• Telescopes and microscopes are
examples of instruments where
the magnification factors are
combined.
Magnification
• Binoculars are basically a pair of
telescopes.
– In this case, the magnification
factor is the same for each
side of the binocular.
• Cameras also use several
lenses.
T/F A lens that looks like
this will focus light.
True
Question