electromagnetic radiation

Electromagnetic Radiation

Physics

Relax and Enjoy the Ride… It’s quite a ride.

Waves… a reviewMost waves are either longitudinal or transverse.

Sound waves are longitudinal.

But all electromagnetic waves are transverse…

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Wave Relationships

Notice from the definitions we can relate the properties of a wave to one another

periodfrequency 1

wavelengthvelocity wavelength frequency

period

Wave Relationships Frequency is usually expressed in the unit of Hertz

This unit is named after a German scientist who studied radio waves

For example, if a wave has a period of 10 seconds, the frequency of the wave would be 1/10 Hz, or 0.1 Hz

sHz

11

Note that light is always traveling at the same speed

(c ~ 3 x 108 m/s)

Remember: velocity = wavelength x frequency

If frequency increases, wavelength decreases If frequency decreases, wavelength increases

Electromagnetic wavesProduced 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 DualityLight can behave like a wave or like a particle

A “particle” of light is called a photon

Radio wavesLongest wavelength EM wavesUses:

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

MicrowavesWavelengths from 1 mm- 1 mUses:

Microwave ovens Bluetooth headsets Broadband Wireless Internet Radar GPS

Infrared RadiationWavelengths in between microwaves and visible light

Uses: Night vision goggles Remote controls Heat-seeking missiles

Visible lightOnly 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

Wavelengths of Light - Visible

What we see as white light is actually made up of a continuum of components

Traditionally, we break white light into red, orange, yellow, green, blue, indigo, and violet (ROY G BIV)

There is actually a continuous transition of color, each with its own wavelength and frequency

UltravioletShorter 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-raysTiny wavelength, high energy waves

Uses: Medical imaging Airport security Inspecting industrial welds

Gamma RaysSmallest wavelengths, highest energy EM waves

Uses Food irradiation Cancer treatment Treating wood flooring

Blackbody Radiation

Cool gas ( ~60K)

Young star ( ~600K)

The Sun (~6000K)

Hot stars in a cluster ( ~60,000K)

The Sun at Different Wavelengths

Visible Ultraviolet

X-ray X-ray

With a traditional optical telescope, the space between stars and galaxies (the background) is completely dark. However, a sufficiently sensitive radio telescope shows a faint background glow, almost exactly the same in all directions, that is not associated with any star, galaxy, or other object. This glow is strongest in the microwave region of the radio spectrum. The CMB's serendipitous discovery in 1964 by American radio astronomers Arno Penzias and Robert Wilson was the culmination of work initiated in the 1940s, and earned them the 1978 Nobel Prize.

Doppler Effect

The motion of an object can be measured through a change in the frequency of the waves emitted by the object

The increase in pitch of an approaching police car is caused by the compression of the sound wave The pitch decreases as the police car moves away

Doppler Shift

In astronomy, the same effect happens to light waves

A source that is moving away will appear redder (redshift)

A source that is moving toward us will appear bluer (blueshift)

Note: Only objects moving toward or away from us (radial motion) will show this effect

EM Spectrum HW:p. 389 # 1-3, 31-35

Powerpoint CreditsJ. Beauchemin 2009 free online ppt

Image credits1. http://www.antonine-education.co.uk/New_items/MUS/imag

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2548f4bd1.jpg?v=121742987914. http://intamod.com.au/images/uv2.JPG15. http://science.hq.nasa.gov/kids/imagers/ems/

xrays.html16. http://www.sciencelearn.org.nz/var/

sciencelearn/storage/images/contexts/see_through_body/sci_media/neck_x_ray/17945-5-eng-NZ/neck_x_ray_full_size_portrait.jpg

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