1. Section 4.6—Light

2. Light is Electromagnetic Radiation
Electromagnetic energy is energy that has electric and magnetic fields
Electromagnetic energy travels in waves at the speed of light “c” (3.0 × 108 m/s)

3. Types of Electromagnetic Radiation
Visible light
400 nm
700 nm
10-12
10-10
10-8
10-6
10-4
10-2 1
102
104
106
Wavelengths (cm)
Cosmic
Rays
Gamma X-
Ultraviolet
Infrared
Microwaves
Radio waves
Electric
Power
Notice that LIGHT is only one type of electromagnetic radiation.

5. Wave Properties—Frequency
Frequency () is the number of times a wave completes a cycle in one second (cycles per second is “Hertz” or “Hz” = 1/s)
Lower frequency
Higher frequency

6. Wave Properties—Wavelength
Wavelength () is the distance from trough to trough of a wave (measured in meters “m” and in metrix prefix units of pm,nm etc.)
wavelength

7. 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 = 
E= h h is a constant so if  goes up so does E

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

10. 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”
Clicking on the active link above allows you to visualize the photons!! Yeah! 

11. Section 4.7—Light & Matter

12. Electrons Absorbing Energy
If a Photon collides with an electron on an atom it transfers that energy to the electron. Photons are energy! - +

13. Electrons Absorbing Energy
If a Photon collides with an electron on an atom it transfers that energy to the electron. Photons are energy!
Photons can be light energy! So when we shine light on electrons they get excited!!!
Notice that the purple light excited it two energy levels. Lower energy, such as blue might only excite it to jump up one level. - +
The electron is “excited” to a higher energy level with its newly increased energy from absorbing the photon.

14. Excitation
Excitation Definition: The process of an electron absorbing a photon of light (energy) and being promoted to a higher energy level from its “ground state”

15. And later…
The electron cannot remain in that excited state indefinitely - +

16. And later…
The electron cannot remain in that excited state indefinitely so it falls back down!! - +
Energy is released – the electron relaxes

18. Energy of photon and levels jumped
The higher the energy of the photon, the greater the electron jump!
A photon of UV light has more energy than a photon of Infrared light
The UV photon would cause a higher energy jump (jump up more levels) than the IR photon.

19. Total energy in = Total energy out
However much energy was absorbed must be released again..

20. Measuring light absorption

21. Hydrogen Spectrum
Hydrogen has a unique spectrum! As do all elements! It is like their fingerprint!!!! 
The black bars are the colors that a hydrogen atom absorbs. The other colors pass through the atom un-absorbed.

22. Ways of producing light
Fluorescence: visible light is absorbed and visible light is emitted at the same
Phosphorescence: Visible light is absorbed and then a while later is
Incandescence: Energy is put in from heat and given off as visible light
Chemiluminescence: Energy released during a chemical reaction is absorbed to cause excitation. Relaxation produces visible light
Biolouminescence: Chemiluminescence that occurs in a biological organism.