Key Concepts in Waves and Quantum Mechanics

Amplitude

The maximum amount that a particle in the medium will displace from its normal equilibrium position when a wave passes through the medium.

Anti-node

A location of maximum vibration in a standing wave.

Compression wave

A wave in which the molecules of the medium vibrate in the same direction as the wave propagates—also known as a longitudinal wave.

Constructive interference

When two or more waves passing through the same space at the same time both disturb the medium in the same way so that the resulting amplitude is larger than the amplitudes of the individual waves or, in other words, higher parts get higher and lower parts get lower.

Destructive interference

When two of more waves passing through the same space at the same time both disturb the medium in opposite ways so the resulting amplitude is smaller than the amplitudes of the individual waves.

Diffraction

The changing of direction of waves to bend around corners and spread as waves encounter obstacles. Diffraction is most noticeable when the wavelength of the wave is about the same size as the obstacle or opening.

Doppler effect

A change in the observed frequency of a wave occurring when the source of the wave and the observer are in motion relative to each other.

Frequency

The number of wave amplitude crests that pass a particular point in space every second.

Interference

The canceling and enhancing effect that occurs when two or more waves move through the same space at the same time.

Longitudinal wave

See compression wave.

Mechanical wave

A traveling disturbance in a material that transports energy.

Medium

Material through which a wave may travel; for example, the medium for the sound waves we hear is generally air, but water or another material may also be the medium.

Node

A location of no vibration in a standing wave.

Reflection

The act of a wave bouncing off a surface.

Refraction

The act of a wave changing direction when the wave passes from one medium to another.

Shear force

A sideways acting force.

Shear wave

A wave in which the molecules of the medium vibrate at right angles to the direction the wave propagates—also known as a transverse wave.

Standing wave

A wave where the locations of constructive interference and destructive interference are stationary.

Surface wave

A wave that travels along the surface of a medium.

Transverse wave

See shear wave.

Wavelength

The distance between successive similar parts in a repeating wave.

Wave speed

The rate at which a specific wave disturbance travels from point to point.

Maxwell's equations

A set of four fundamental laws expressed in mathematical form that govern electricity and magnetism and their interrelationship.

Photoelectric effect

The ejection of electrons from metals when light is shone on the metals' surface.

Photon

A particle of light; it has no mass, no charge, and possesses energy, frequency, and wavelength.

Wave-particle duality

Possessing both wave and particle properties.

Boiling point

See boiling temperature.

Boiling temperature

The temperature at which a substance changes from a liquid to a gas or vice versa.

Compression force

A force that is applied in such a way as to compress (flatten or squish) a material.

Continuous spectrum

A spectrum in which the colors blend gradually together without noticeable abrupt changes or missing colors.

Diffraction grating

A series of very fine, closely spaced lines.

Discrete spectrum

A spectrum of separate and distinct colors in which all colors are not present.

Gas

Physical state of matter characterized by the material being able to change both shape and volume to match the container.

Ionic conductors

Materials that do not conduct electricity in the solid state but do conduct when molten or dissolved in water.

Liquid

Physical state of matter characterized by the material being resistant to changes in volume but the material will change shape to match the container.

Melting point

See melting temperature.

Melting temperature

The temperature at which a substance changes from a solid to a liquid or vice versa.

Plasma

Physical state of matter characterized by the positive and negative charges in the fluid being able to move separately.

Solid

Physical state of matter characterized by the material being resistant to changes in size and shape.

Spectrum

A range of electromagnetic radiation arranged by wavelength or frequency.

States of matter

Physical condition that describes matter—namely, solid, liquid, gas, plasma.

Tension force

A force that is applied in such a way as to stretch a material.

Brownian motion

The random motion of particles such as dust or pollen in a liquid when viewed with a microscope.

Molecular model of matter

(1) Molecules are very tiny particles that make up matter; (2) different kinds of matter are made up of different molecules; (3) the molecules in matter are constantly moving about, sometimes colliding with one another; and (4) the motion of the molecules is governed by the laws of motion, force, and conservation.

Absorption spectrum

The set of dark lines that are missing from a continuous spectrum of light after the light has passed through a gas.

Emission spectrum

The set of colors of light given off (or emitted) by an object.

Excited state

A state of an electron (or nucleus, in later chapters) where the electron is not at the lowest possible energy level.

Ion

A charged atom or molecule.

State

A particular condition of a physical system. It is the set of properties that allow you to make predictions about the behavior of the system.

Heisenberg uncertainty principle

The uncertainty in an object's position times the uncertainty in an object's momentum must be greater than or equal to Planck's constant.

Probability curve

A curve giving the probability of where an object might be detected. Locations that are high on the curve indicate where the object is most likely to be found.

Probability wave

A probability curve that moves in time and space.

Quantum mechanics

A branch of physics used to describe the wave properties of light and matter.

Uncertainty principle

See Heisenberg uncertainty principle.

Electronic structure

Shorthand notation for what orbitals are occupied in a particular atom.

Energy level diagram

A diagram showing the energies of the different orbitals in an atom. The energy of the orbitals (and electrons) increase as one moves up a level.

Exclusion principle

Only two electrons are allowed in one orbital, and the two electrons in the same orbital must differ by spin.

Orbital

A standing wave of probability describing the probability of finding an electron around the nucleus of an atom.

Shell

A group of orbitals having similar energies and sizes.

Spin

A magnetic characteristic of an electron that is related to its intrinsic angular momentum and is usually detected using magnetic fields.

Atomic mass

Mass per unit atom, generally equal to the number of protons and neutrons.

Atomic number

Number of protons in a nucleus. This number defines an element.

Atomic weight

The average atomic mass of all naturally-occurring forms of a particular atom.

Compound

Two or more chemical elements that are chemically combined.

Element

Matter that contains only one type of atom.

Family

Elements that are grouped together because they have similar chemical properties and the same number of valence electrons.

Group

See family.

Ionization energy

Energy required to remove one electron from an atom.

Main group

Metals and nonmetals designated with "A" column headings in the periodic table.

Metal

Elements that conduct electricity.

Nonmetal

Elements that do not conduct electricity.

Period

Elements in horizontal rows of the periodic table.

Subshell

S and p orbitals in a shell.

Transition metals

Metals in the middle of the table designated with "B" column headings.

Valence electrons

The electrons in the outermost shell of an atom.