Light and the Electromagnetic Spectrum

Wave Vocabulary The frequency (f) of a wave is the number of waves to cross a point in 1 second (units are Hertz) The wavelength (λ) - the length of a wave. Crest to crest, Units of distance vary depending on size of the wave.

What’s special about these waves? The waves that make up the E.M. spectrum are like notes on a piano or keyboard. The “low” notes have long wavelengths and a low frequency. The “high” notes have short waves and short frequency.

The Electromagnetic Spectrum The waves on the Electromagnetic Spectrum are different than sound waves because they do not require a medium to travel through. They go wherever they want to and it’s what allows them to travel through space!

Order of the Waves Radio Gamma Microwaves X-rays Infrared Ultraviolet Left Side Right Side Lowest frequency Highest frequency Lowest Energy Highest Energy Longest Wavelength Shortest Wavelength Radio Gamma Microwaves X-rays Infrared Ultraviolet Visible

Radio Waves Radio waves have the longest wavelengths and lowest frequency. Uses include communications like the radio in your car, satellite television, and airplanes.

Microwaves A microwave oven passes microwaves through water molecules causing them to vibrate against one another. Microwaves are also used for communication in devices like your telephones and some satellite communications. Also used for radar, like what you see in Doppler Radar and in speed cameras like the big signs and police speed guns.

Infrared Light (below red) Infrared waves are associated with heat. Lamps, fireplaces, and even your body give off infrared waves. We can see them on thermographic images. Infrared can be found in short range communication devices like your TV remote, and found in some versions of night vision goggles.

RedOrangeYellowGreenBlueIndigoViolet Visible light represents a small portion of the whole spectrum. This is the only part that our eyes can detect. What we see is are all the colors (wavelengths) of the rainbow. RedOrangeYellowGreenBlueIndigoViolet Light waves are used to create lasers which have a variety of uses. (Printers, DVD players)

Fun Facts about visible light Fun Facts about visible light! Your eyes are most sensitive to a wavelength that is around the 550 nm. (That is the same color as this background) This wavelength is the wave in which the Sun emits most of its energy in the visible part of the spectrum. So over time, our eyes (and other things like plants) have evolved to be the most receptive to this wavelength to maximize the energy from the sun.

Why is the sky blue?

But then why does the sunset look red?

Ultraviolet (beyond violet) UV light is found in tanning beds and insect lamps. (Insects can see those waves even though we we can’t) The sun emits powerful UV rays, but most are absorbed by the ozone layer. Too much exposure to UV waves will burn our skin! UV waves are used to sterilize equipment in hospitals and our lab safety goggles.

X-Rays X-rays are used in the medical profession to take images of bones and body parts. X-rays are used in airports to check luggage as well as people. Astronomers will study X-rays given off by stars and other objects in our solar system. X-rays are dangerous if you are continuously exposed. They can cause cell death and cancer.

Gamma Rays Gamma rays are the highest energy type of waves. The are byproducts of the waste in a nuclear reaction or nuclear explosion. Due to their high energy content, even a short exposure can cause cancers or cause death. They can be used to treat cancer or be used in radioactive tracers in low dose.

End of ER Spectrum

Light sabre demo/discussion- last chance if not done yet.

HONORS ONLY: Light Equations

All electromagnetic waves travel at the same speed. (3.0 x 108 m/sec) That’s the speed of light! Using that number, we can determine the relationship between frequency and wavelength. C = λf C = Speed of light (3.0 x 108 m/sec) λ = Wavelength (meters) F = Frequency (Hertz or cycles/sec)

Calculate the wavelength of the yellow wave created from a sodium lamp if the frequency of the wave is 5.10 x 1014 Hz. List the known info List the unknown C = 3.00 x 108 m/s λ (wavelength) = ? M F = 5.10 x 1014 s-1 C = λf λ = 3.00 x 108 m/s = 5.88 x 10-7 m 5.10 x 1014 s-1

YOUR TURN 1) What is the wavelength of radiation with a frequency of 1.50 x 1013 s-1? 2) What frequency does a wave vibrate if it has a wavelength of 4.00 x 10-3 m?

Atoms and Light The vibration of electrons produce energy in the form of photons/waves. Each element has its own signature of spectral lines allowing us to identify it based on its energy emission.

When an electron vibrates between energy levels, it gives off energy in the form of a photon, or wave of a specific wavelength. The wavelengths given off in spectral lines relate to the distance the electron travel between energy levels. Knowing the wavelength and frequency of the wave allows us to determine the amount of energy it has. This relationship can be calculated using Planks constant.

Planck’s law relates the energy of a photon to its frequency or wavelength: h = Planck’s constant c = speed of light = wavelength of light Planck’s Constant (h) is a constant value and is equal to 6.625 x 10–34 J s or

Orange light has a wavelength of 6.20 x10-7 m What is its frequency? C = λf 3.00 x 108 m/s = 6.20 x10-7m  (f) f = 4.84 x 1014 hz (b) Determine the energy for one photon of orange light. E = hf E = 6.625 x 10-34 J/sec x 4.84 x 1014 hz Energy = 3.21 x 10-19 J

A certain frequency of wave is needed or the effect will not work. The photoelectric effect – When light shines on metals, electrons are ejected from their surface. These moving electrons can be used as electricty! A certain frequency of wave is needed or the effect will not work. Red light will not cause electrons to eject! b/c it is a lower energy wave Green or Blue light will work because they are higher energy waves and cause electrons to “eject” and move.