Key Concepts in Electromagnetic Radiation and Spectroscopy

absorption spectrum

a series or pattern of dark lines superimposed on a continuous spectrum

blackbody

an idealized object that absorbs all electromagnetic energy that falls onto it

continuous spectrum

a spectrum of light composed of radiation of a continuous range of wavelengths or colors, rather than only certain discrete wavelengths

dispersion

separation of different wavelengths of white light through refraction of different amounts

Doppler effect

the apparent change in wavelength or frequency of the radiation from a source due to its relative motion away from or toward the observer

electromagnetic radiation

radiation consisting of waves propagated through regularly varying electric and magnetic fields and traveling at the speed of light

electromagnetic spectrum

the whole array or family of electromagnetic waves, from radio to gamma rays

emission spectrum

a series or pattern of bright lines superimposed on a continuous spectrum

energy flux

the amount of energy passing through a unit area (for example, 1 square meter) per second; the units of flux are watts per square meter

energy level

a particular level, or amount, of energy possessed by an atom or ion above the energy it possesses in its least energetic state; also used to refer to the states of energy an electron can have in an atom

excitation

the process of giving an atom or an ion an amount of energy greater than it has in its lowest energy (ground) state

frequency

the number of waves that cross a given point per unit time (in radiation)

gamma rays

photons (of electromagnetic radiation) of energy with wavelengths no longer than 0.01 nanometer; the most energetic form of electromagnetic radiation

ground state

the lowest energy state of an atom

infrared

electromagnetic radiation of wavelength 10^3 - 10^6 nanometers; longer than the longest (red) wavelengths that can be perceived by the eye, but shorter than radio wavelengths

inverse square law (for light)

the amount of energy (light) flowing through a given area in a given time decreases in proportion to the square of the distance from the source of energy or light

ion

an atom that has become electrically charged by the addition or loss of one or more electrons

ionization

the process by which an atom gains or loses electrons

isotope

any of two or more forms of the same element whose atoms have the same number of protons but different numbers of neutrons

microwave

electromagnetic radiation of wavelengths from 1 millimeter to 1 meter; longer than infrared but shorter than radio waves

nucleus (of an atom)

the massive part of an atom, composed mostly of protons and neutrons, and about which the electrons revolve

photon

a discrete unit (or "packet") of electromagnetic energy

radial velocity

motion toward or away from the observer; the component of relative velocity that lies in the line of sight

radio waves

all electromagnetic waves longer than microwaves, including radar waves and AM radio waves

spectrometer

an instrument for obtaining a spectrum; in astronomy, usually attached to a telescope to record the spectrum of a star, galaxy, or other astronomical object

Stefan-Boltzmann law

a formula from which the rate at which a blackbody radiates energy can be computed; the total rate of energy emission from a unit area of a blackbody is proportional to the fourth power of its absolute temperature: F = σT^4

ultraviolet

electromagnetic radiation of wavelengths 10 to 400 nanometers; shorter than the shortest visible wavelengths

visible light

electromagnetic radiation with wavelengths of roughly 400-700 nanometers; visible to the human eye

wavelength

the distance from crest to crest or trough to trough in a wave

Wien's law

formula that relates the temperature of a blackbody to the wavelength at which it emits the greatest intensity of radiation

X-rays

electromagnetic radiation with wavelengths between 0.01 nanometer and 20 nanometers; intermediate between those of ultraviolet radiation and gamma rays

infrared

electromagnetic radiation of wavelength 103-106 nanometers; longer than the longest (red) wavelengths that can be perceived by the eye, but shorter than radio wavelengths

Electromagnetic radiation

A form of energy that exhibits wave-like behavior and can behave as particles called photons.

Wavelength (λ)

The distance between successive peaks of a wave, which determines the color of visible radiation.

Frequency (f)

The number of cycles of a wave that pass a point in a given time period, related to wavelength and speed of light by the equation c = λf.

Speed of light (c)

The constant speed at which light travels in a vacuum, approximately 299,792 kilometers per second.

Photon

A packet of energy that represents a quantum of electromagnetic radiation.

Inverse square law

A principle stating that the apparent brightness of a source of electromagnetic energy decreases with the square of the distance from the source.

Electromagnetic spectrum

The range of all types of electromagnetic radiation, including gamma rays, X-rays, ultraviolet radiation, visible light, infrared, and radio radiation.

Wien's law

A mathematical equation that describes the relationship between the temperature of an idealized emitter of electromagnetic radiation and the wavelength at which the maximum amount of radiation is emitted.

Stefan-Boltzmann law

A law that states the total power emitted per square meter increases with increasing temperature.

Spectrometer

A device that forms a spectrum, often utilizing the phenomenon of dispersion.

Continuous spectrum

A spectrum that shows a continuous range of colors without any gaps.

Emission spectrum

A spectrum that consists of bright lines or bands, indicating the wavelengths of light emitted by a source.

Absorption spectrum

A spectrum that consists of dark lines or bands, indicating the wavelengths of light absorbed by a substance.

Atom

The basic unit of a chemical element, consisting of a nucleus and electrons.

Nucleus

The central part of an atom, containing positively charged protons and, in most cases, neutrons.

Proton

A positively charged particle found in the nucleus of an atom, defining the element.

Neutron

A neutral particle found in the nucleus of an atom, contributing to the atomic mass.

Electron

A negatively charged particle that orbits the nucleus of an atom.

Isotope

Atoms of the same element with the same number of protons but different numbers of neutrons.

Bohr model

A model of the atom that describes electrons in permitted orbits around the nucleus.

Planck's formula

The equation E = hf, which relates the energy of a photon to the frequency of the electromagnetic wave it represents.

Ground state

The lowest energy level of an atom.

Excited state

A state of an atom in which an electron is in an orbit other than the least energetic one possible.

Ion

An atom that has lost one or more electrons, resulting in a net electric charge.

Spectra of different ions

Can tell astronomers about the temperatures of the sources they are observing.

Doppler Effect

The shift in spectral lines due to the motion of an atom toward or away from an observer, indicating radial velocities of distant objects.

Blue shift

Occurs when an atom is moving toward us, causing a spectral line to shift slightly toward the blue of its normal wavelength.

Red shift

Occurs when an atom is moving away from us, causing a spectral line to shift toward the red.

Radial velocities

The velocities of distant objects measured using the Doppler effect.

Electromagnetic Spectrum

The range of all types of electromagnetic radiation, which includes visible light, radio waves, and X-rays.

Quantum Mechanics

A fundamental theory in physics describing the physical properties of nature at the scale of atoms and subatomic particles.

Household lightbulb spectra

The type of spectra expected to be seen from a household lightbulb using a spectrometer.

Sun spectra

The type of spectra expected to be seen from the Sun using a spectrometer.

Neon lights spectra

The type of spectra expected to be seen from the 'neon lights of Broadway' using a spectrometer.

Ordinary household flashlight spectra

The type of spectra expected to be seen from an ordinary household flashlight using a spectrometer.

Streetlight spectra

The type of spectra expected to be seen from a streetlight on a busy shopping street using a spectrometer.

Broadcast radio frequencies

The frequencies that a radio can tune to, which include various words and symbols indicating different stations.

Frequency of a radio station

The specific frequency that a favorite radio station broadcasts on.

Wavelength of a radio station

The wavelength corresponding to the frequency of a favorite radio station.

Electromagnetic wave technology

Technologies that utilize electromagnetic waves, which can be listed by individuals in a group activity.

Applications of the Doppler effect

Everyday life applications of the Doppler effect, such as its use by highway patrol.

Alien civilization communication

Discussing the best band of the electromagnetic spectrum to send a message to an alien civilization with a similar atmosphere to Earth.

NASA Mission Science video tour

A video tour of the bands of the electromagnetic spectrum provided by NASA.

Doppler ball demonstration

A demonstration video explaining the Doppler effect and its application to satellites.

Prism and rainbow colors

A short video explaining how a prism bends light to create a rainbow of colors.

Electromagnetic radiation

A form of energy that travels through space and can be categorized into different types based on wavelength and frequency.

Wave

A disturbance that transfers energy through space or matter, characterized by its wavelength and frequency.

Wavelength

The distance between successive crests of a wave, typically measured in meters.

Frequency

The number of waves that pass a given point per second, measured in hertz (Hz).

Emission lines

Bright lines in a spectrum that occur when electrons in an atom drop to a lower energy level and emit light.

Absorption lines

Dark lines in a spectrum that occur when electrons in an atom absorb specific wavelengths of light and move to a higher energy level.

Doppler effect

The change in frequency or wavelength of a wave in relation to an observer moving relative to the source of the wave.

Bohr's model

A model of the atom that describes electrons in fixed orbits around the nucleus, incorporating Maxwell's work on electromagnetic radiation.

Electromagnetic radiation (astronomical context)

Radiation that includes visible light, radio waves, gamma rays, and X-rays, used to study cosmic objects.

Light waves vs. sound waves

Light waves are electromagnetic waves that can travel through a vacuum, while sound waves are mechanical waves that require a medium to travel.

Ionosphere

A region of Earth's upper atmosphere that interacts with radio waves, affecting their propagation.

Gamma rays

High-energy electromagnetic radiation that is more dangerous to living things than X-rays.

Dispersion

The separation of light into its component colors, used by astronomers to study the light from stars.

Joseph Fraunhofer

A scientist who discovered dark lines in stellar spectra, known as Fraunhofer lines, which indicate the presence of specific elements.

Rutherford's gold foil experiment

An experiment that demonstrated the existence of a small, dense nucleus in the atom, leading to a revised atomic model.

Isotopes of hydrogen

The three isotopes are protium, deuterium, and tritium, differing in the number of neutrons in their nuclei.

Blueshifted

The term used for objects moving toward us, indicating that their spectral lines are shifted to shorter wavelengths.

Redshifted

The term used for objects moving away from us, indicating that their spectral lines are shifted to longer wavelengths.

Spectral absorption and emission lines

Used to determine the composition of a gas by analyzing the specific wavelengths of light absorbed or emitted.

Maxwell's theory of electromagnetic waves

A theory that describes how electric and magnetic fields propagate through space, leading to various practical applications.

Cosmic objects

Astronomical entities such as stars, gas clouds, and galaxies that can be studied through their emitted or absorbed light.

X-rays

Dangerous due to their high energy and ability to ionize atoms.

Radio waves

Much less dangerous due to their lower energy and non-ionizing nature.