Ch 16 NATURE OF LIGHT
Updated
6/20/03
Menu
Diffraction: Hair Diameter: http://chem.lapeer.org/PhysicsDocs/Goals2000/Laser2.html
1
a] Diagram labels include the pulsating electric force field, pulsating
magnetic force field,
the velocity vector + its magnitude 3x108 m/s or 186,000 mi/s.
It could travel around the Earth's equator 7 times in one second.
b] Light is mutually reinforcing, perpendicular, pulsating, electric and
magnetic force fields.
c] Electromagnetic spectrum. [see p
411], indicate Hi & Low frequency, wavelength, and energy, along with
ROYGBIV.
Since the speed of light is constant, if we know the frequency we can find the
wavelength with the wave equation: Speed = frequency x wavelength, c = fL
To identify the type of light, we need only the frequency or the wavelength but
not both.
TYPE
OF LIGHT WILL
BE PRODUCED OR ABSORBED BY:
GAMMA RAYS REARRANGEMENT
OF THE PARTICLES IN THE NUCLEUS;
X RAYS REARRANGEMENT
OF THE INNER ELECTRONS IN ATOMS;
ULTRAVIOLET REARRANGEMENT OF THE MIDDLE ELECTRONS;
VISIBLE LIGHT REARRANGEMENT
OF THE OUTER ELECTRONS
[narrow range 400-700 nm = 1 octave, ear--20-20,000 Hz = 1000 octaves]
INFRARED VIBRATIONS
OF ATOMS & MOLECULES
MICROWAVES SPECIALIZED
ELECTRON VACUUM TUBES
TV & RADIO WAVES
OSCILLATING ELECTRIC CURRENTS
THE
5 EFFECTS OF LIGHT.
HEAT: SOLAR HEATING & THE
GREENHOUSE EFFECT
BIOLOGICAL: SKIN MAKES VITAMIN D;
UV OVEREXPOSURE CAUSES SKIN CANCER
PHOTOCHEMICAL: PHOTOSYNTHESIS;
PHOTOGRAPHY, DECOMPOSITION (BLEACHING)
PHOTOELECTRIC: SOME ELEMENTS GIVE
OFF SMALL ELECTRIC CURRENTS OR
CONDUCT
ELECTRICITY WHEN STRUCK BY LIGHT--USED IN ELECTRIC EYES,
PHOTOCOPIERS,
CALCULATORS
FLUORESCENCE: SOME CHEMICALS GIVE
OFF LIGHT WHEN EXPOSED TO
UV, OR
X-RAYS--FLUORESCENT LIGHTS; OR ELECTRON BEAMS--TV
4
a] ULTRAVIOLET LIGHT IS USED TO STERILIZE FOOD AND MEDICAL EQUIPMENT
[ABSORBED BY DNA]. INFRARED LIGHT
IS USED TO WARM FOOD.
b] MEDICINES, BEER, WINE, PEROXIDE ARE STORED IN BROWN, GREEN, OR OPAQUE
CONTAINERS TO PREVENT CHEMICAL DECOMPOSITION.
5
Emission
Spectra are mostly dark with a few thin stripes of color.
This indicates that electrons are allowed in only certain energy levels.
Electrons gain energy from friction, chemical & nuclear reactions,
etc, and move to a specific higher energy levels.
When they fall to a lower energy state they give off wavelengths (color)
specific to their individual compounds and elements.
The possible energy transitions are:
7 ---> 6
7 ---> 5 6
---> 5&
7 ---> 4 6
---> 4& 5 --->
4
7 ---> 3 6
---> 3& 5 --->
3 4 ---> 3
7 ---> 2 6
---> 2& 5 --->
2 4 ---> 2
3 ---> 2
7 ---> 1 6
---> 1& 5 --->
1 4 ---> 1
3 ---> 1 2
---> 1&
7 ---> 0 6
---> 0& 5 --->
0 4 ---> 0
3 ---> 0 2
---> 0& 1 --->
0
The larger energy transitions (7 ---> 0, 6 ---> 0, 5 ---> 0, 4 --->
0) are in the ultraviolet range, the middle transitions are in the visible range
and the lower are in the infrared range. Below
is the simplest energy graph, that for a hydrogen atom.
(An important aspect, the energy transitions, which should be drawn in
different colors are missing.)
Shell#
6 & 7 |________________________________________
E
5|----------------------------------------
N
4|----------------------------------------
E
|
R
3|----------------------------------------
G
|
Y
|
2|----------------------------------------
L
|
E
|
V
1|----------------------------------------
E
|
L
|
|
0|_______________________________________
6a
TWO METHODS & 7 WAYS OF GENERATING LIGHT.
BOOSTING e- INTO HIGHER ENERGY LEVELS
1 MECHANICAL
(FRICTION)--INCANDESCENT LIGHT
2 CHEMICAL--FIRE,
FIRE FLIES, GLOW STICKS
3 NUCLEAR--SUN
4 OPTICAL--BOMBARDMENT
W/ U.V.--FLUORESCENT LIGHTS
5 ELECTRICAL--BOMBARDMENT
W/ ELECTRONS--TV
ACCELERATING ELECTRONS
6 DECELERATING
ELECTRONS--X-RAYS
7 VIBRATING
ELECTRONS--RADIO & T.V. TRANSMISSION
6b
/\E = hf /\E
= the electron's change in energy
h = a constant
f = the frequency of the
light produced or absorbed.
6c
a] Incandescent bulb: friction
between the electrons & the wire heats the wire.
The heat boosts the electrons in the metal into a higher energy level,
when they fall to a lower level they give off light.
b] Fire, lightning bugs, glow sticks: heat
or energy from a chemical reaction boosts the electrons in the gas into a higher
energy level, when they fall to a lower level they give off light.
c] Sun: heat from a nuclear reaction boosts the electrons in the plasma into a
higher energy level, when they fall to a lower level they give off light.
d] Florescent lights use ultraviolet light to boost the electrons in the powder
coating the inside of the glass tube into higher energy levels.
When the electrons fall back to a lower energy level they give off light.
If you change the powder you change the color.
e] TV’s shoot electrons at a fluorescent screen, boosting the electrons in the
fluorescent material into a higher energy level, when they fall to a lower level
they give off light. (One e- gun for each color)
Cathode
Ray Tube
+------------------------------------------+
|
Vacuum Tube |
| Front
of TV
----------0 Heated
|
|
0 Metal
| |
Fluorescent
| 0
Coil e---->
| Coated
----------0 Positively
Negatively | |
Glass
|
| Charged
Charged |
|
|
Screen |
|
+------------------------------------------+
|
|
| + Terminal | |
- Terminal |
+--------------||||----------------+
| |
Voltage
source (battery)
f] X-Ray machines make light by shooting electrons at a metal target, when they
decelerate to give off X-Rays. Diagram
(see board)
+--------------------------------------------+
|
Vacuum Tube
|
----------0 Heated
X-Rays --> |
|
0 Metal
High Speed
|
|
|
0 Coil
e---->
| |
----------0 Positively
Negatively | Metal |
|
| Charged
Charged | Target |
|
|
|
|
+--------------------------------------------+
| 20,000
V
|
| + Terminal | |
- Terminal |
+--------------||||--------------+
| |
20,000 V Voltage
source (strong battery)
g] Radio Stations make light by accelerating electrons in the form of
vibrations. Ex:
KYW vibrates electrons at 1060 kHz
Translate two of these methods (not optical) into a sentence or two.
7
The speed of light.
*
Moon Jupiter's
Moon hides behind Jupiter for a short
time
in its orbit. If you start a clock
when it
appears
from behind Jupiter you can predict when
it
will appear six months later. Your prediction
Jupiter will
be off by 1000 sec, the time it takes light
to
transverse the diameter of Earth's orbit.
D = 2 x 93,000,000 mi = 186,000,000, mi
D
Speed of Light = c = -
t
*
-------------Earth at Start
|
186,000,000
mi
|
c = -------------- =
186,000 mi/s
|
1,000 s
|
|
Sun
|
D = 186,000,000 mi
|
|
|
|
___________| Earth 6 months later.
8
See pg 414 for sample problems.
9a
Light travels in straight lines is the property that determines the
geometry of the Light Transmission Diagram. (See Heath, pg 415).
a] Make a triangle by drawing 2 diagonal lines from the margin to the edge of
your paper. At the edge the lines
will be 10 rows apart.
b] Drop a vertical where the diagonal line crosses the 1st, 2nd,
& 3rd blue lines.
c] For each vertical measure the distance between the two diagonal lines.
d] Use this distance to draw a square with its upper left corner at the where
the 3rd diagonal crosses the blue line.
e] Using the right hand corners of this square draw two Red diagonals.
f] Draw the 2 smaller squares by using the red lines to anchor the right hand
corners of these squares.
Description:
1] All the light that goes through
1 ft2
at a distance of 1 unit is spread over 4 ft2
and 9 ft2 at a
distances of 2 and 3 units.
2] Generally: The light per square
ft decreases as the square of the distance from the source.
That is, the illumination is inversely proportional to the distance from
the source squared. E = I/D2
9b
I = Intensity = the brightness of a source (light bulb), candelas, cd
E = Illumination, the light per unit area that falls on a target, candelas/m2
= Lux, E = I/D2
D = the distance between the source and the target.
P = the power or energy/sec needed to run the light bulb, watts, J/sec.
Heath
Ch 17 Color
Updated 5/26/03
Top
7
a] ANY GREEN OBJECT REFLECTS ___ AND ABSORBS ___
b] THE DIFFERENT COLORS IN WHITE LIGHT ARE CREATED BY DIFFERENT FREQUENCIES.
ANY OBJECT HAS THE COLOR IT REFLECTS AND ABSORBS THE OTHERS.
EX: ANY RED OBJECT REFLECTS
RED AND ABSORBS ALL THE OTHER COLORS.
8
ADDITIVE COLOR PROCESS USED IN TV
3 PRIMARY COLORS OF LIGHT WITH THE CORRECT INTENSITY = WHITE LIGHT.
THE ONLY ONES THAT FULFILL THAT REQUIREMENT ARE RED, GREEN, & BLUE.
<----------------------LIGHT---------------------->
PRIMARY | 2 PRIMARY
= SECONDARY | COMPLIMENTARY
RED |RED + GREEN = YELLOW
| YELLOW & BLUE
GREEN |RED + BLUE = MAGENTA
| MAGNETA & GREEN
BLUE |BLUE + GREEN =
CYAN | CYAN & RED
PRIMARY + SECONDARY = WHITE
PRIMARY PIGMENTS ABSORB ONLY 1 COLOR FROM WHITE LIGHT AND REFLECTS 2
SECONDARY PIGMENTS ABSORB 2 COLOR FROM WHITE LIGHT AND REFLECTS ONLY 1
THE ONLY ONES THAT FULFILL THAT REQUIREMENT ARE
<--------------------------PIGMENTS-------------------------->
PRIMARY | ABSORBS | REFLECTS
|| SECONDARY | ABSORBS
YELLOW | BLUE | RED +
GREEN || BLUE
| RED & GREEN
MAGENTA | GREEN | RED
+ BLUE ||
GREEN | RED
& BLUE
CYAN | RED | BLUE + GREEN ||
RED |
GREEN & BLUE
PRIMARY + SECONDARY = BLACK
OBJECT IN LIGHT LOOKS
RED OBJECT IN GREEN OR BLUE
LIGHT LOOKS BLACK
GREEN OBJECT IN RED OR BLUE
LIGHT LOOKS BLACK
BLUE OBJECT IN GREEN OR RED
LIGHT LOOKS BLACK
8
a] THE RULES OF COLOR ARE
b] TWO PRIMARY COLORS COMBINE TO FORM A SECONDARY COLOR
c] THE 3 SECONDARY COLORS ARE YELLOW, CYAN, MAGENTA
d] IF RED LIGHT & GREEN LIGHT ARE MIXED THE RESULT APPEARS YELLOW.
e] THE THREE PRIMARY COLORS OF LIGHT COMBINE TO FORM WHITE LIGHT.
8
a] THE PRIMARY COLORS OF LIGHT ARE RED, GREEN, BLUE
b] TWO PRIMARY COLORS COMBINE TO FORM A SECONDARY COLOR
c] THE 3 SECONDARY COLORS ARE YELLOW, CYAN, MAGENTA
d] IF RED LIGHT & GREEN LIGHT ARE MIXED THE RESULT APPEARS YELLOW.
e] THE THREE PRIMARY COLORS OF LIGHT COMBINE TO FORM WHITE LIGHT.
9
a] THE 3 PRIMARY PIGMENTS ARE YELLOW, CYAN, MAGENTA
b] PRIMARY PIGMENTS ABSORB 1 PRIMARY COLOR FROM WHITE LIGHT, & REFLECTS THE
OTHER TWO.
c] A SECONDARY PIGMENT ABSORBS 2 PRIMARY COLORS FROM WHITE LIGHT.
d] THE 3 SECONDARY PIGMENTS ARE RED, GREEN, BLUE
e] A PRIMARY PIGMENT AND A SECONDARY PIGMENT ABSORB ALL LIGHT.
10
OBJECTS THAT ALLOW LIGHT TO PASS ARE ___
TRANSPARENT
OBJECTS THAT ALLOW SHADOWS TO PASS ARE ____
TRANSLUCENT
OBJECTS THAT DO NOT ALLOW ANY LIGHT TO PASS ARE ___ OPAQUE
11
FOR AN OBJECT TO BE TRANSPARNET OR OPAQUE DEPENDS UPON ___, ___, &
___
GIVE 2 EXAMPLES.
"VISIBILITY" DEPENDS ON THE SOURCE, THE FILTER, & THE RECEIVER
[diagram]
OBJECTS OPAQUE TO ONE FREQUENCY MAY BE TRANSPARENT TO OTHERS.
BRICK IS TRANSPARENT TO GAMMA RAYS &
OPAQUE TO ALL OTHERS
ALUMINUM FOIL "
"
" X-RAYS "
" "
VISIBLE LIGHT
CLEAR GLASS "
"
" VISIBLE LIGHT &
TRANSLUCENT TO UV
12
a] DRAW A DIAGRAM SHOWING HOW ROUGH IRREGULAR SURFACES REFLECT LIGHT.
b] ROUGH IRREGULAR SURFACES ___ REFLECED LIGHT, CALLED ___LIGHT.
SCATTER DIFFUSED
13
DRAW & LABEL A DIAGRAM SHOWING HOW POLARIZED LIGHT IS MADE.
[Fig 17-12,13, p 296]
ELECTROMAGNETIC WAVE, SECTION-->VIBRATES ALL PLANES
YOU SEE ONLY THE PLANE THAT SATISFIES THE LAW OF REFLECTION==>
GLARE--LIGHT REFLECTED OFF A SMOOTH SURFACE [GLASS/WATER] IS POLARIZED.
SOME SUN GLASSES AND CAMERA LENSES ARE POLARIZED TO ELIMINATE GLARE.
14
a] BECAUSE LASER LIGHT IS
COHERENT IT CAN BE DIRECTED AT ANY POINT TO WITHIN ONE WAVELENGTH OR ONE
MILLIONTH OF A METER.
b] NAME 6 USES OF LASERS.
[1] READ BAR CODES [2] READ CD's [3] SURVEYING, [4] SURGERY, [5] HOLOGRAPHY [3D
PICTURES], & [6] PHONE COMMUNICATIONS.
c] WHAT DOES THE ACRONYM LASER
STAND FOR?
Light Amplification by Stimulated Emission of Radiation.
15
a] DRAW & LABEL A
DIAGRAM SHOWING HOW LIGHT IS MADE.
WHEN AN ENERGIZED ELECTRON FALLS BACK TO THE GROUND STATE IT EMITS A PHOTON OF
LIGHT WITH A SPECIFIC FREQUENCY [f = /\E/h]
b] WHAT IS COHERENT LIGHT?
[DIAGRAM] LIGHT WAVES HAVE THE SAME
FREQUENCY & ARE ALL IN PHASE--THE SAME CREST & TROUGH POINTS.
c] WHY DO SOME MATERIALS PRODUCE
COHERENT LIGHT AND OTHERS DON'T?
FOR COHERENT LIGHT TO BE MADE ALL THE ELECTRONS MUST DROP BETWEEN THE SAME 2
ENERGY LEVELS ALL AT ONCE. THIS
WILL ONLY HAPPEN IN MATERIALS WHICH STORE THE e- FOR A RELATIVELY LONG TIME
[10-12 s], I.E.,WITH METASTABLE ENERGY STATES
d] WHAT IS STIMULATED EMMISSON?
ELECTRONS STORED IN AN EXCITED STATE CAN BE STIMULATED TO EMIT LIGHT BY HITTING
IT WITH A PHOTON OF THE CORRECT FREQUENCY [f = /\E/h].
IT WILL EMIT AN ADDITIONAL PHOTON OF THE SAME FREQUENCY & IN PHASE.
DIAGRAM.
e] DRAW & LABEL THE DIAGRAM OF
A LASER. PHOTON, ENERGIZED ELECTRON, AMPLIFICATION, 100% REFLECTIVE, 98%
REFLECTIVE, 2% BEAM ==> ON AVG 50 ROUND TRIPS BEFORE LEAVING, BEAM IS ALL ONE
FREQUENCY & IN PHASE.
Top
Menu
|