Electromagnetic Energy

Waves… a reviewMost waves are either

longitudinal or transverse.Sound waves are longitudinal.But all electromagnetic waves

are transverse…

?

?

Electromagnetic waves Produced by the movement of

electrically charged particles Can travel in a “vacuum” (they do

NOT need a medium Travel at the speed of

light Also known as EM waves

Wave-particle Duality Light can behave like a wave or like a

particle A “particle” of light is called a photon

Radio waves Longest wavelength EM waves Uses:

TV broadcasting AM and FM broadcast radio Avalanche beacons Heart rate monitors Cell phone communication

Microwaves Wavelengths from 1 mm- 1 m Uses:

Microwave ovens Bluetooth headsets Broadband Wireless Internet Radar GPS

Infrared Radiation Wavelengths in between microwaves

and visible light Uses:

Night vision goggles Remote controls Heat-seeking missiles

Visible light Only type of EM wave able to be

detected by the human eye Violet is the highest frequency light Red light is the lowest frequency

light

Ultraviolet Shorter wavelengths than visible

light Uses:

Black lights Sterilizing medical equipment Water disinfection Security images on money

Ultraviolet (cont.)UVA UVB and UVC

Energy Highest of UV waves

Lower than UVA

Health risks

Extremely low risk for DNA damage Can destroy Vitamin A in skin

Can cause DNA damage, leading to skin cancer Responsible for sunburn

X-rays Tiny wavelength, high

energy waves Uses:

Medical imaging Airport security Inspecting industrial welds

Gamma Rays Smallest wavelengths, highest

energy EM waves Uses

Food irradiation Cancer treatment Treating wood flooring

Calculations with Waves Frequency: number of wave peaks

that occur in a unit of time Measured in Hertz (Hz) Represented by nu (v)

Wavelength: the distance between wave peaks Represented by lambda (λ)

c= λv, c=3.0 x 108 m/s

Understanding Wavelength/Frequency

If the wavelength is longer, the frequency is low

If the wavelength is shorter, the frequency is high

Practice

A certain green light has a frequency of 6.26 x 1014 Hz.

What is its wavelength?

Max Planck Assumed energy was given off in little

packets, or quanta (quantum theory) He called these quanta photons. He determined the energy of this quanta of

light could be calculated

E=hvE: quantum of energy

h: constant, 6.626 x 10-34 J/Hzv: frequency of the wave

Practice

What is the energy content of one quantum of the light in the previous problem?

Bohr Model of Atom Proposes that the atom is

“quantized” As electrons move around the nucleus, they

have specific energies Only certain electron orbits (energy levels) are

allowable

Bohr Model Atoms are most stable when their

electrons are orbiting around the atom with the lowest possible energies. This lowest energy state is the ground state.

If the electrons absorb energy, the atom can leave the ground state and jump to a higher energy state called the excited state.

Bohr Model The electron jump (a quantum leap)

occurs when an atom absorbs a packet of electromagnetic energy called a photon.

Only photons of certain energies are absorbed during this process

Quantum Leaps Create a high energy state for the

atom which is not favored by nature and is unstable

Electrons immediately release the energy that they absorbed to return back to ground state

Energy Released The energy is released as specific

energies of visible light which we see as different colors

Types of Spectra Absorption (dark-line) spectra appear as a

rainbow of colors with dark lines in it. Each dark line represents a specific amount of energy that an electron absorbs as it quantum leaps into a higher energy orbit

Types of Spectra Emission (bright-line) spectra appear as a dark

background with lines of color in it. Each colored line represents a specific amount of energy that an electron releases as it quantum leaps back to its original orbit.

What do you notice?

Analyzing Spectra Analysis of the spectra of different

substances is the basis for spectroscopy The study of the energy which is given off and

absorbed when atoms go from the ground state to the excited state and back again

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