Electromagnetic Energy http://www.jessb.org

Waves… a review Most waves are either longitudinal or transverse. Sound waves are longitudinal. But all electromagnetic waves are transverse…

? ? Prompt students to guess what the teal box, then the blue box, is hiding. (Wavelength, Amplitude)

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

Clicking the little rainbow box at the top of each slide will bring you back to this one

Radio waves Longest wavelength EM waves Uses: TV broadcasting AM and FM broadcast radio Avalanche beacons Heart rate monitors Cell phone communication Click the little rainbow box in the top right corner to return to the overview EM spectrum diagram

Microwaves Wavelengths from 1 mm- 1 m Uses: Microwave ovens Bluetooth headsets Broadband Wireless Internet Radar GPS Click the little rainbow box in the top right corner to return to the overview EM spectrum diagram

Infrared Radiation Wavelengths in between microwaves and visible light Uses: Night vision goggles Remote controls Heat-seeking missiles Click the little rainbow box in the top right corner to return to the overview EM spectrum diagram

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 Click the little rainbow box in the top right corner to return to the overview EM spectrum diagram

Ultraviolet Shorter wavelengths than visible light Uses: Black lights Sterilizing medical equipment Water disinfection Security images on money There is one more UV slide…

X-rays Tiny wavelength, high energy waves Uses: Medical imaging Airport security Inspecting industrial welds Click the little rainbow box in the top right corner to return to the overview EM spectrum diagram

Gamma Rays Smallest wavelengths, highest energy EM waves Uses Food irradiation Cancer treatment Treating wood flooring Click the little rainbow box in the top right corner to return to the overview EM spectrum diagram

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?

v: frequency of the wave 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=hv E: quantum of energy h: constant, 6.626 x 10-34 J/Hz v: 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 https://www.youtube.com/watch?v=KQ3Xom5XAM4

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