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# Electromagnetic waves and the electromagnetic spectrum

Learn how electromagnetic waves are formed from changing electric and magnetic fields. Understand the electromagnetic spectrum, including different regions from visible light to gamma rays and their uses. Created by David SantoPietro.

## Want to join the conversation?

• The way this is drawn, with B up and E toward us would represent a wave direction going to the left, not to the right. The right hand rule is such that if your fingers are along E and they curl in the direction of B (same as the direction your palm faces) then your thumb sticking out perpendicular points in the direction of the electromagnetic wave, so in your example you'd need to switch the B and E fields drawn to have a wave going to the right.
• Yes the direction of the propagation would be to the left and not the right
• Are the infrared, micro and radio waves harmful for us?
• As given in my textbook
radio waves don't cause any hazards(but they maybe harmful)
microwaves cause Internal heating of the body tissue(which is harmful)
Infra-red waves cause skin burns
• How does something like ink or paint (or the pixels on my computer) change the way light is reflected so that it is seen in different colors?
• Ink and paint absorb light of certain wavelengths and reflect others. These are subtractive colors. When you only mix a few colors, the combination will only reflect colors that all of the original ones reflect. That is why you get black or dark brown when you mix a bunch of paints together.
Pixels, on the other hand, emit light, rather than reflect it. These are additive colors. For most computers and TVs, there are red, blue, and two green LEDs in pixels, but some fancy screens also have yellow. There are two greens because our eyes are most sensitive to green, around 550 nm wavelength. When you want white light, all of the LEDs light up; when you want black, all are dim. For any color in between, the screen lights up the appropriate LEDs the appropriate amounts to get the mix of these colors to be the color you want.
• If x-rays are more energetic than UV rays, then is the reason we are burned by UV rays (sunburn) a function of being exposed to them for longer? Would we receive similar burns from an x-ray if exposed for a similar period of time?
• Yes, and we would get DNA damage that can cause cancer.
• Difference b/w AM and FM radio?
• AM is amplitude modulation and FM is frequency modulation. In AM transmissions the strength the signal is varied to transmit the information. In FM the frequency is varied to transmit the information.
• If what we see as color is the spectrum of visible electromagnetic waves, why do only objects appear to have color and not the space between them?
• Because objects reflect the electromagnetic waves into our eyes where we can see them. Space just lets the waves pass through it so they don't hit our eyes
• in a projector to display text black color is used ,a projector projects light where does the black light come from?
• Black in a computer is actually multiple colors together. Look closely at Pixelated letters to see Many colors. Sometimes, depending on the age of the computer connected to the Projector, the black is , like Teacher Mackenzie said, lack of light. If I am mistaken, please feel free to correct me!
• Does anyone know how microwaves got their name? I had the misconception that their name indicated either their wavelength or frequency range but that is incorrect.
• Hello Jacob,

Radio is old! The technology and vocabulary grew up over the last century. You are correct "micro: is not μ or 10^-6. Rather, it is a relative comparison of the waveform size to the traditional frequencies.

You should know that the size of a radio antenna is a function of the frequency to be transmitted / received. The antenna follows:

λ = c/f

The microwave antenna for operation at 1 GHz would be microscopic compared to the antenna for a 1 MHz broadcast station.

You may be interested in these links:

http://www.csgnetwork.com/freqwavelengthcalc.html:
https://en.wikipedia.org/wiki/Regenerative_circuit
https://en.wikipedia.org/wiki/Microwave

Regards,

APD