Chapter 7: Light and Color
semiconductor or diode lasers
Although they produce only modest power, these lasers can be made cheaply and have found utility in supermarket scanners, laser pointers, CD players, and other electronic equipment.
3.0 x 10^8 m/s, 186,000 mi/s
Nothing is known to travel faster than light, which moves at _________, or __________.
wave, particle
One of the complexities of light is related to its dual nature; it has both ______ and ____ properties.
aligned, in phase
One of the differences between laser light and ordinary light is the alignment of the electromagnetic waves. In contrast to ordinary light, whose electromagnetic waves are randomly oriented, laser light contains waves whose troughs and crests are __________, or _______.
400, 780
Only a small fraction of all electromagnetic radiation, called the visible region, can be seen by human eyes. The visible region is bracketed by wavelengths of _____ nm (violet) to ______ nm (red).
photons
Particles of light which are tiny packets of energy traveling at the speed of light.
spacings
The color of an object depends on the energy _______ between the electron orbits of the molecules and atoms that compose the object.
fast, slow
The difference between fluorescence and phosphorescence is the time required for electrons to relax--fluorescence is relatively _____, and phosphorescence is ______.
Heinrich Hertz
The discoverer of radio waves.
energy state
The electron configuration of a molecule or atom with electrons in particular orbits is called an _________.
difference
The energy of the photon (which depends on its wavelength) must be exactly equal to the energy ________ between the two orbits.
resonance frequency
The exact electromagnetic frequency that causes a transition is called the _________.
photodecomposition
The fading of fabrics on repeated exposure to sunlight is due to _____________.
chlorophylls
The green-blue-yellow light reflected from a green leaf makes the leaf appear a dark shade of green. The molecules responsible for this green color are ___________.
metal ion
The lasing medium in a solid-state laser is usually a _________ distributed in a solid crystal.
organic dye
The lasing medium in dye lasers is an ________ in a liquid solution.
tube
The lasing medium in gas lasers is a gas or a mixture of gases contained in a ________.
radio waves
The longest of all wavelengths are ________ with wavelengths as long as football fields.
helium-neon
The most common gas laser is the ___________ laser named after the gases present in its cavity.
carbon dioxide laser
This is the most efficient and powerful of all gas lasers producing high powers--up to 1000 watts (W). Such a beam can easily cut through steel and is used in welding, drilling, and cutting.
magnetic resonance imaging (MRI)
Today, doctors have a powerful technology to look into the human body. This technology is based on the spectroscopy of hydrogen atoms in a magnetic field and is called _______________.
solid-state, gas, dye, and semiconductor (diode lasers)
Types of lasers.
electromagnetic radiation
A general term for all forms of light.
absorption spectrum
A graph that shows the intensity of these changes as a function of the radio wave frequency is called an ________.
magnetic field
It is the area around a magnet where forces are experienced.
fluorescence
An example of relaxation through light emission is the glow of a white T-shirt under black light. Black lights emit UV light, invisible to our eyes but capable of exciting electrons in the white T-shirt. As the electrons relax, they emit visible light in a process called _________.
infrared (IR) light
At longer wavelengths than visible light is _________.
wavelength
It is the distance between wave crests and it determines the color of the light.
red, orange
Carotenes, responsible for the color of carrots, absorb all colors except _____ and ______.
ultraviolet (UV) light
Electromagnetic radiation of slightly shorter wavelengths than violet light is called ___________.
radio wave
For NMR, the resonance frequency occurs in the ________ region of the electromagnetic spectrum.
ground energy state (or simply ground state)
If all electrons are in the lowest-energy orbits possible, the atom or molecule is in the ___________.
photodecomposition
If the energy of the absorbed photon is high enough, usually in the UV region or higher, bonds, within the molecule can break, and the molecule may fall apart. We call this process ____________, and it is partly responsible for the dangers of UV light, X-rays, and gamma rays.
black
If the molecules absorb all light, there is no reflected light, and the object appears _____.
white
If the molecules do not absorb any light, the reflected light is _____, and the object appears _____.
colored
If the molecules in an object selectively absorb some of light's colors and reflect others, the object appears ______.
(electronic) relaxation
In __________, the electron falls back to its original orbit, producing heat or light in the process.
lasing medium
In a laser, molecules or atoms within the ________ are excited with light or electrical energy.
laser cavity
In a laser, the lasing medium is placed inside a __________ consisting of two mirrors, one of which is only partially reflecting.
one
In contrast to white light, which contains many wavelengths, laser light contains only ______.
photodecomposition, relaxation
In summary, the excitation of electrons in molecules can result in __________--in which molecules break down to other substances--or __________.
carotenes
In the fall, chemical reactions within leaves destroy the chlorophyll molecules and a different class of molecules, called _______, dominates the leaf's color.
frequency
It is a property of light that is the number of cycles or crests that pass through a stationary point in 1s.
UV light
It is invisible to our eyes and has enough energy in its photons to break chemical bonds and damage biological molecules.
electric field
It is the area around a charged particle where forces are experienced.
relaxation time
MRI can measure the time required for nuclei to return to their original orientation after being pushed by electromagnetic radiation. The time required for realignment--or more correctly, relaxation--is called the __________ and is very sensitive to the local environment.
spectroscopy
Scientists use the interaction of light with matter, called __________, to identify unknown substances.
shorter, higher
The _____ the wavelength, the ______ the frequency.
inverse, increases, decreases
The relationship between the wavelength and energy of light is an _____ relationship, meaning that as the wavelength ______, the energy ________.
gamma rays
The shortest of all wavelengths and the most energetic form of electromagnetic radiation.
tunability
The unique feature of dye lasers.
semiconductor or diode lasers
The very smallest, and in many cases the most inexpensive.
magnetic, electric
The wave nature of light is embodied in _________ and _______ fields.
light amplification by stimulated emission of radiation
The world laser is an acronym for _________.
argon ion
They are the lasers which are used in rock concerts to produce spectacular effects.
dye lasers
They have found numerous applications in basic scientific research and in medicine.
microwave (radiation)
They have longer wavelengths but have lower energy than visible or IR. The energy they give off is efficiently absorbed by water molecules.
hydrogen, nuclear magnetic resonance (NMR)
Unlike the spectroscopy discussed previously that involves electrons, MRI involves the nuclei of ______ atoms and was originally termed _____________.
phosphorescence
We see the emission of light in _________, which occurs in glow-in-the dark toys.
excited state
When the electron is in the higher-energy orbit, the atom or molecule is said to be in an _________.
