# Electromagnetic Waves

## Presentation on theme: "Electromagnetic Waves"— Presentation transcript:

Electromagnetic Waves
are made by vibrating electrical forces that travel through space – but do NOT require matter to travel

Electromagnetic Waves have a wavelength and a frequency:
Wavelength = the distance between the crest of two waves Frequency = the number of waves that pass a point in 1 second The energy of a wave is related to wavelength and frequency – how?

The Electromagnetic Spectrum
Is composed of energy having different wavelengths and frequencies Higher frequency waves = more energy. The energy we detect with our eyes is   VISIBLE LIGHT

The speed of energy waves in space is referred to as "speed of light"
This is nature's speed limit – we know of nothing that travels faster! If travel is to occur to distant planets and galaxies, we need to find a way to exceed the speed of light!

Radio Waves We are surrounded by radio waves that we cannot see.
(Where are they on the electromagnetic spectrum?)  The radio or TV antenna receives the radio waves and converts them to different forms of energy - sound waves or light waves that you can hear or see. Radio waves have different frequencies for each station/supplier. You tune your radio or TV receivers by choosing a frequency.

Radar - uses radio waves to find the position and movement of objects
stands for RAdio Detecting And Ranging Radar devices measure the time required for radio waves to bounce off an object, like a car. The measured time is converted into the object’s positions (and thus, speed).

Microwaves Microwave ovens turn electricity into microwaves. that causes water molecules to move back and forth, which in turn causes HEAT. Intense microwaves can damage living cells and tissue – hence, they are enclosed by strong metal boxes that do not allow the waves to escape. Weak microwaves can carry information – such as those used by cellphones.

Infrared Waves – transmit heat, and are used to detect living creatures in the absence of visible light. Objects that are living (use energy or that metabolize food) can be distinguished from the environment by infrared waves.

Ultraviolet (UV) Waves have shorter wavelengths and more energy than visible light, and can enter cells. A small amount may be good, but too much can cause sunburn and cause blisters and damage your DNA

X Rays and Gamma Rays Both are high energy waves and are damaging if you are exposed to them without protection X Rays can be used to form images of bone and teeth (how do these Work for Superman?) Gamma Rays - can be used to target and kill cancer cells (radiation therapy)

Visible Light  Violet = shortest wavelength seen Red = longest wavelength seen

Transparent materials (glass, water, plastic) pass visible light, but may block UV and infrared waves. Glass is not transparent to most UV, this is why you cannot get a sunburn through a window.

Opaque - materials that are not transparent
Tights are labeled as either sheer (transparent) or opaque; which ones are pictured here ?

Why is wet sand darker than dry sand?
Light reflecting from a dry surface goes directly to your eyes.  However, as light is reflected from wet surface, some of it is scattered and absorbed - making it appear darker.  The ocean and sky are blue because water and air absorb red light and scatter blue light that we see. At sunset and sunrise, we can see sunlight that is not reflected, but do not look very long – as it may damage your eyes!

Color is determined by the receiver – which perceives the wavelength of light that reflects from or is emitted by an object. What color is..... The sky? ______________________ An apple?  ______________________ The grass ? ______________________ Can you explain why?

If you are colorblind, you cannot perceive which colors?
Can you explain why?

How we see colors depends on whether the object absorbs or reflects particular wavelengths.
White objects reflect all visible light Black objects absorb all visible light White light passed through a prism causes the different energy wavelengths to separate, which are perceived as individual colors.

Primary Colors Red, Green & Blue are the primary colors.  These colors combine to create any other color in the visible spectrum.    All three combined will create white light. Red + Blue = magenta (purple) Blue + Yellow = green Red + Yellow = orange Opposites on this color wheel contain all three primary colors and form white light.