Finish spectrum, visible light, energy of EM waves

Type of wave Wavelength Source Uses Danger Interesting

Radio λ> 30 cm Types of transmitters, stars, sparks, and lightning

Communication None.

Microwave 30cm >λ> 1mm

magnetron. Radar, microwave ovens, communication, weather radar

Cataracts, being “cooked”Microwave ovens are shielded (look for the thin wire mesh in the door)

People who work on aircraft carrier decks wear special suits which reflect microwaves, to avoid being "cooked" by the powerful radar units in modern military planes.

Infrared 1mm >λ> 700nm

Hot objects, including flames, stars, and warm bodies

Weather, TV remotes, heal sports injuries, alarms.

Overheating Night vision goggles, weapon targeting systems,

Visible 700nm >λ> 400 nm

Anything hot enough to glow

Vision, CD players, laser pointers

Damage to retina if you look at something too bright for too long

Ultraviolet 400nm >λ> 60 nm

UV lights, VERY hot objects such as the sun

Sun burns, astronomy

Sunburn, skin cancer, and damage to retina

Be sure to get sunglasses that block UV radiation

X Ray 60nm >λ> 10-4 nm

Stars and nebula, X-ray machines.

To see inside people or luggage, astronomy

Cancer, damage to cells and DNA

X-ray machine works by firing a electron beam at a target.

Gamma Ray λ<0.1nm Stars and radioactive substances

Sterilize medical equipment and food, radiation treatment

Cancer, mutations, and kills cells

Radios: How do they work? AM radio: AM stands for

amplitude modulation. Set frequency but radio

station varies the amplitude

Problems Lots of natural and man-

made noise. Weak signals are quieter

than strong ones.

Radios: How do they work? FM radio: FM stands for

frequency modulation. Set amplitude but radio

station varies the frequency

Microwave ovens

Water. There are trillions of water molecules in a single drop. The temperature of the water depends on the motion of the molecules. They move with respect to each other and vibrate. The hotter the water, the more activity.

Microwaves continued

Water molecules absorb microwaves at a certain frequency. This extra energy causes an increased amount of vibrations in the molecules.

As the water molecules vibrate, they bump into other molecules, transferring energy or heat.

Visible Light

A few things you need to know: For Violet light, λ= 400 nm For red light, λ= 700 nm

Example: Compare the frequency of red light compared to violet light.

Visible Light

c=fλ Plug in the numbers Red λ= 700 nm = 700*10-9 m Violet λ= 400 nm = 400*10-9 m C=3.00*108 m/s

Frequency of Red light=4.3*1014 Hz Frequency of Violet light=7.5*1014 Hz Notice the trend, Violet has a higher

frequency than Red

Light Particle

Photon—A discrete unit of light energy

A photon is “localized energy”

Energy of a Photon

E=hf Energy = constant * frequency h=Planck’s constant=6.626*10-34 J * Sec

Example

What is the energy of a photon of green light? Wavelength = 550nm

The equation is E=hf. First, find the frequency of green light.

λ=550 nm = 550*10-9 m C=f λ, f=5.45*1014Hz

E=hf, h=6.62*10-34Jsec E=3.60*10-19 J

Example 2

If the energy of a photon is 2.5*10-18 J, what is the frequency of that photon? What is the wavelength?

Answer: Frequency =3.77*1015 Hz Wavelength = 7.944*10-8 m