Electromagnetic Electromagnetic SpectrumSpectrum

Range of BehaviorRange of Behavior Electromagnetic waves are Electromagnetic waves are

characterized by their characterized by their wavelength or frequency.wavelength or frequency.• Linked by the speed of lightLinked by the speed of light

The frequency is associated The frequency is associated with an energy.with an energy.• High frequency is high energyHigh frequency is high energy

The common unit is the The common unit is the electron-volt (eV).electron-volt (eV).• Work done by 1 V potential on Work done by 1 V potential on

one electronone electron

hc = 1.240 keV nm

c

hchE

Electromagnetic RadiationElectromagnetic Radiation

Traditional upper boundaries for types of EM radiation:Traditional upper boundaries for types of EM radiation:

(m)(m) (Hz)(Hz) E E (eV)(eV) Radio waves Radio waves 11 33101088 1.241.241010-6-6

MicrowavesMicrowaves 111010-3-3 3310101111 1.241.241010--

33

InfraredInfrared 0.750.751010-6-6 4410101414

1.651.65 Visible lightVisible light 0.40.41010-6-6 7.57.510101414 3.13.1 Ultraviolet lightUltraviolet light 1.21.21010-8-8 2.42.410101616 11101022

X-raysX-rays 1.41.41010-11-11 3310101919 1.21.2101055

Gamma rays Gamma rays (highest energy)(highest energy)

Radio WavesRadio Waves Radio waves primarily come Radio waves primarily come

from the oscillation of currents from the oscillation of currents in conductors.in conductors.

A 1 MHz frequency has an A 1 MHz frequency has an energy of 6.6 x 10energy of 6.6 x 10-28-28 J. J.

The long wavelengths travel The long wavelengths travel easily and are not interfered by easily and are not interfered by atoms.atoms.• Except conductorsExcept conductors

MicrowavesMicrowaves Microwaves are very short Microwaves are very short

wavelength radio waves.wavelength radio waves.

Microwaves are associated Microwaves are associated with the vibrations of some with the vibrations of some atoms and molecules.atoms and molecules.

Water molecules act as a Water molecules act as a dipole.dipole.• Motion increased by Motion increased by

microwavesmicrowaves

• Causes heating Causes heating

Radiation from HeatRadiation from Heat Heated objects give off Heated objects give off

electromagnetic waves.electromagnetic waves.• Higher temperature has more Higher temperature has more

radiationradiation

A hot object gives off a A hot object gives off a spectrum of frequencies.spectrum of frequencies.• Shifts based on temperatureShifts based on temperature

This is called blackbody This is called blackbody radiationradiation

low energy

high energy

frequency

intensity

InfraredInfrared Molecules are heated by Molecules are heated by

infrared waves.infrared waves.• Radiant heatRadiant heat

Wavelengths longer than Wavelengths longer than visible light are called infrared visible light are called infrared rays.rays.• Come from warm objectsCome from warm objects

Visible LightVisible Light Visible light is radiation in a Visible light is radiation in a

narrow band of wavelength.narrow band of wavelength.• 400 nm to 800 nm400 nm to 800 nm

• Narrower ranges are colorsNarrower ranges are colors

Corresponds to maximum Corresponds to maximum output from the Sun.output from the Sun.

Many atoms and molecules Many atoms and molecules have specific behavior at have specific behavior at unique frequencies of light.unique frequencies of light.

low energy

high energy

frequency

intensity

UltravioletUltraviolet Ultraviolet rays have shorter Ultraviolet rays have shorter

wavelengths than visible light.wavelengths than visible light.• Higher energyHigher energy

• Often with visible lightOften with visible light

Some molecules absorb Some molecules absorb ultraviolet and reemit visible ultraviolet and reemit visible light.light.• Fluorescent lightFluorescent light

X-RaysX-Rays X-rays are associated with X-rays are associated with

energetic transitions in atoms.energetic transitions in atoms.

Continuous spectra result from Continuous spectra result from electron bombardment.electron bombardment.

The short wavelength x-rays The short wavelength x-rays can penetrate materials.can penetrate materials.• Stopped by dense atomsStopped by dense atoms

target

electrons

x-ray

Gamma RaysGamma Rays Gamma rays are photons Gamma rays are photons

associated with nuclear or associated with nuclear or particle processes.particle processes.• Energy range overlaps: soft Energy range overlaps: soft

gamma equals hard x-raygamma equals hard x-ray

Acceleration of a very Acceleration of a very energetic charged particle energetic charged particle gives x-rays and gamma rays.gives x-rays and gamma rays.• Called bremsstrahlungCalled bremsstrahlung

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