Electromagnetic Radiation Conceptual Physics    J. Beauchemin 2009

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

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 When an electric field changes, so does the magnetic field. The changing magnetic field causes the electric field to change. When one field vibrates—so does the other.  RESULT-An electromagnetic wave. Click here  Animation: Interaction of vibrating chargesInteraction of vibrating charges

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

EM Spectrum Defined  Electromagnetic Spectrum—name for the range of electromagnetic waves when placed in order of increasing frequency, decreasing wavelength.

B. Waves of the Electromagnetic Spectrum  Click here  (Animation—Size of EMwaves)—Size

Radio waves  Longest wavelength EM waves  Uses: TV broadcasting AM and FM broadcast radio Heart rate monitors Cell phone communication

Radio Transmission  A transmitter produces an electrical current. This energy is transmitted to an antenna.  The antenna produces electromagnetic waves (radio waves) that get sent through space.  The receiving antenna picks up and converts the radio waves into sound that we can hear

AM vs FM

Microwaves  Wavelengths from 1 mm- 1 m  Uses: Microwave ovens Bluetooth headsets Broadband Wireless Internet Radar GPS

Microwaves  Microwaves are sent through and “excite” the atoms that make up food, which results in heat energy.

Infrared Radiation  Wavelengths in between microwaves and visible light  Uses: Night vision goggles Remote controls Heat-seeking missiles

IR  Anything that emits heat will emit IR. So all of us are emitting Infrared radiation right now!  IR can be used to “see” heat

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

UV Health Risks  Skin cancer  Cataracts  Suppression of the immune system  Premature aging of the skin

When are UV rays the strongest?  UV rays tend to be stronger in the summer and at noon, when the sun is highest in the sky. The UV Index forecasts the strength of the sun’s harmful rays. The higher the number, the greater the chance of sun damage.

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

 X-rays work because x-rays pass through soft tissue, but not hard tissues like bone. The x-rays that pass through the soft tissue are detected and the image is then generated.

Gamma Rays  Smallest wavelengths, highest energy EM waves  Uses Food irradiation Cancer treatment Treating wood flooring

 All stars produce gamma rays, but massive stars produce the most!  Gamma ray bursts are produces when a star explodes or goes supernova  Gamma rays from the sun do not reach earth because our atmosphere filters them out!

Using the EM waves to view the Sun AnimationAnimation—View a Galaxy at different wavelengths

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