Electromagnetic Energy

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

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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.) UVAUVB and UVC EnergyHighest 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 10 8 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 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=hv E: quantum of energy h: constant, x 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

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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