1. Sec Light and Matter

2. Light Light- a form of electromagnetic radiation
Electromagnetic radiation- energy in wave form that has electric and magnetic fields
Every wave of electromagnetic radiation travels at the speed of light
There is a huge range of different types of electromagnetic radiation- only a very small portion of all radiation is visible!

3. Electromagnetic Spectrum

4. Wave Properties
Waves have several defining properties- crest, trough, frequency and wavelength
Crest- highest point on wave
Trough- Lowest point on wave

5. Frequency- measures the number of times a wave completes a cycle in one second (cycles per second are “Hertz”, shortened as “Hz”)
High frequency:
Low frequency:

6. Wavelength- the length between two adjacent crests or two adjacent troughs- measured in meters
Large wavelength:
Small Wavelength:

7. When a wave has a high frequency, what is true about it’s wavelength
When a wave has a high frequency, what is true about it’s wavelength? Look back at your wave diagrams
When a wave has a low frequency, what is true about it’s wavelength?
From this, how are wavelength and frequency related?

8. The frequency of a wave, as well as the wavelength is related to the energy that wave has
When a wave has a high frequency, it has a high amount of energy, and vice versa

9. When a wave has a large wavelength, it will have a small amount of energy, and vice versa
For a wave with high energy, it will have a high frequency, and a low wavelength

10. Visible range
Visible light has a fairly small range in wavelengths- 400nm-700nm
Different wavelength values correspond with different colors…which means different colors correspond with different amounts of energy
Visible light
400 nm
700 nm

11. Which color of light has the highest energy?
Which color of light has the lowest amount of energy?
ROYGBIV

12. Photons- Quantized
Electromagnetic radiation travels in “packets” called photons
Photon= light packet
Must have full photons- cannot have fractions of photons
Radiation is said to be “quantized” because of this- it comes in certain amounts of photons

13. Light Interaction with Matter
Ground State- most stable electron configuration- electrons occupy the lowest energy levels they possibly can
When photons of light run into atoms, the electrons in the atom can absorb the photon

14. When electrons absorb photons, they are able to “hop” to higher energy levels- being further away from the nucleus requires more energy
Excited state- when electrons jump to higher energy levels

15. The difference between the ground state and the excited state will be equal to the energy of the photon
The process of electrons absorbing photons and jumping to higher energy levels is known as excitation
Excited state- higher energy, but not very stable

16. Electrons will not remain in an excited state for long- they will want to return to ground state
When electrons return to ground state, they must release energy
When electrons release energy, they release it as a photon

17. How much energy will this released photon have?
Relaxation- process of an excited electron releasing energy and returning to ground state

18. Drawing Excitation and Relaxation

19. Released Energy is Unique
Every element has a unique set of energy levels
Due to these unique sets of energy levels, each element will absorb/release different (and unique) amounts of energy

20. Since energy is related to the frequency and wavelength of light- different elements absorb/release different (unique) wavelengths/frequencies of light
Different wavelength of light= different color

21. This is why fireworks explode in different colors- the fireworks have different types of elements in them- causing different colors of light to release
In a way- the color of light a substance releases is a fingerprint- we can use it to identify unknown substances

22. Flame test- by knowing the color of a flame, we can find the amount of energy that excited electrons are releasing- based on that specific energy, we can identify the substance

23. Ways of Producing Light
Fluoresence- when something absorbs light, and releases light immediately afterward- relaxation happens quickly
Phosphorescence- light is absorbed, then released over a period of time- relaxation occurs slowly
Incandescence- when something is heated (electrons are gaining energy from heat, not photons), then releases light during relaxation

24. Chemiluminescence- electrons absorb energy from a chemical reaction to cause excitation, then relaxation produces visible light
Bioluminescence- electrons absorb energy from a chemical reaction that occurs in a biological organism, then relaxation produces visible light
Triboluminesence- when pressure is applied to a crystal to excite electrons, then release light (typically when the crystal shatters)

25. Which form of light production would be responsible for the following examples:
Glowing Algae:
Mixing liquids from glow sticks:
Glow in the dark stars/t-shirt:

26. Light bulb:
Tonic water under UV light:
Wint-o-green Lifesaver sparking when you chomp on it: