1. Section 4.6—Light

2. Light is Electromagnetic Radiation Electromagnetic energy is energy that has electric and magnetic fields There are many types of Electromagnetic Radiation…visible is just one type! Electromagnetic energy travels in waves at the speed of light “c” (3.0 × 10 8 m/s)

3. 10 -12 10 -10 10 -8 10 -6 10 -4 10 -2 110 2 10 4 10 6 Wavelengths (cm) Cosmic Rays Gamma Rays X- Rays Ultraviolet Rays Infrared Rays MicrowavesRadio wavesElectric Power Visible light 400 nm700 nm Types of Electromagnetic Radiation

4. Wave Properties—Frequency Frequency (  ) is the number of times a wave completes a cycle in one second (cycles per second is “Hertz” or “Hz”) Lower frequency Higher frequency

5. Wave Properties—Wavelength Wavelength ( ) is the distance from trough to trough of a wave (measured in meters “m”) wavelength

6. Relationship between wave properties The shorter the wavelength, the higher the frequency The higher the frequency, the higher the energy The speed of light is equal to wavelength (in meters) times frequency (in sec -1 or s -1 or Hz)  c = 

7. Visible Range Visible light 400 nm700 nm Wavelength increases Frequency decreases Energy decreases White light is made of all the colors…a prism can separate white light into a rainbow!

8. Light is Quantized Light is quantized, which means it comes in packets—you can only have certain amounts of it The “packets” are called “photons” The Energy of a photon (in Joules, “J”) is equal to Planck’s constant “h” times frequency)  E = h  where h = 6.63 × 10 -34 Js