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Electromagnetic Waves 17.1 and 17.2

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Kim Baker

on 7 February 2014

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Transcript of Electromagnetic Waves 17.1 and 17.2

Electromagnetic Waves
Sources of EM Waves
* the Sun

* human technology
- Energy that moves in the form of EM waves
- EM waves can travel without a material medium, that is, in a vacuum or space empty of matter
- an EM wave does not lose energy as it moves, it stays constant
- they travel at about 300,000 km/s
- they can transfer energy to the medium itself
- EM waves can respond to a change by reflecting, refracting or diffracting just like mechanical waves do

Refraction - the bending of a wave as it crosses the boundary between two mediums
Reflection- bouncing back of a wave after it strikes a barrier
Diffraction- the spreading out of waves
Electromagnetic Waves
* a disturbance that transfers energy through a field
* also called EM waves
* occur when electrically charged particles move
* has two fields - electric and magnetic
* the most EM waves on Earth are produced by artificial light
Example of a EM wave
Electromagnetic Spectrum
Electromagnetic Spectrum
- smooth, gradual progression from the lowest frequencies to the highest frequencies
- frequency of an EM wave can be determined from its wavelength
- measured in Hz
(hertz-one hertz = one cycle per second)
- different parts of the spectrum include
- radio waves
- microwaves
- infrared light
- visible light
- ultraviolet light
- x-rays
- gamma rays

Transferring Energy
EM waves can transfer energy in two ways:

1) moving potential energy from place to place

2) converts potential energy into kinetic energy by moving the medium back and forth

Example: when microwaves encounter water, they convert electromagnetic energy into heat
How EM waves are formed
EM waves are formed when two fields (electric and magnetic) vibrate at right angles to each other and are perpendicular to the direction the wave is moving

Uses of Electromagnetic Waves
EM waves have different frequencies

- higher frequency (have more electromagnetic vibrations per second, and have more energy)

- lower frequency (have longer wavelengths and have less energy

Ch 17

Visible Light
- part of the EM spectrum that human eyes can see
- we perceive longest wavelengths of visible light as red and the shortest as violet
- it is only about 1/100,000 of the spectrum

Infrared Light
- consists of EM frequencies between visible light and microwaves
- type of radiation most associated with heat
- sometimes called heat rays
- you cannot see infrared radiation, but you can feel it as warmth coming from the Sun, fire, or a radiator
- some animals such as pit viper snakes can actually see infrared light
- scopes and cameras convert radiation into visible wavelengths
Ultraviolet (UV) Light
- consists of frequencies above those of visible light and partially below those of x-rays
- carries more energy
- waves in this range can damage your skin and eyes
- sunblock and UV protection sunglasses are designed to filter out these frequencies
- can be used to sterilize medical instruments and food by killing harmful bacteria
- causes skin to produce vitamin D
- visible to some animals
Radio Waves
- longest wavelength
- lowest frequencies
- lowest energies
- travel easily through atmosphere and many materials
- transmitted by modulation (changing the waves slightly)
* FM (frequency modulation)
* AM (amplitude modulation)
Radios AM/FM signal)
Television pictures (AM signal)

- shorter wavelengths
- higher frequencies
- higher energy
- get the name because they
are shorter than radio waves
- two important technologies
that use microwaves - radar and cell phones

- RADAR means "radio detection and ranging"
- came into wide use during WWII (1939-1945)
- works by transmitting microwaves, receiving reflections of waves from objects in the waves strike and converting these patterns into visual images on the screen

- air traffic controllers
- analyze weather conditions
- measure speed of moving vehicle
Cell Phones
- A cell phone is actually a radio transmitter and receiver that uses microwaves.
- depend on an overlapping network of cells, or areas of land several kilometers in diameter

- high frequency
- high energy
- pass easily through the soft tissue in the body
- many are absorbed by denser matter such as bone
- too much exposure can damage tissue (lead protection- dentist)
Gamma Rays
- highest frequency
- highest energy
- produced by some radioactive substances as well as by the sun and other stars
- can penetrate the soft and hard tissues of the body, killing normal cells and causing cancer cells to develop
- if controlled, destructive power can be beneficial.
- used by doctors to kill cancer cells and fight tumors
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