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 _________.