3. Placemat Activity: Different Types of Light

4. Unit 4: Chapter 10 – Sources and Nature of Light (p.403-410)
Artificial
Genetically modified zebrafish emit visible light when exposed to UV radiation.
Natural
Algae and bacteria are able to emit light naturally
Bioluminescence

5. Bioluminescence

6. What is light?
Light is a form of energy known as electromagnetic waves
When energy is absorbed electrons move to an excited state.
These excited electrons release energy in the form of light.
In other words, the light that is seen is the light that is emitted, NOT ABSORBED
E.g. Chlorophyll is green because it does not absorb green light
Textbook refers to excited atoms not electrons

7. Types of Light Emissions
There are three types of light emissions:
Light from the sun
Light from incandescent
Light from electric discharge

8. Sun light
Hydrogen atoms in the Sun’s core are moving at rapid speeds and colliding with one another
These collisions will sometimes cause two Hydrogen's to fuse together forming Helium.
A fusion reaction
This reaction releases a ton of energy creating light.

9. Sunlight
Sunlight emits white light which is made up of all light colours.

10. Incandescent Light
Incandescent light occurs when a metal is heated to produce light
Tungsten wire is typically used because of its brightness when heated
It is inefficient at producing light since only 5% of the heat used produces light.
The other 95% is lost as heat

11. Incandescent Demonstration Copper Penny
Why might an older penny ( ) be more effective at producing light when heated?

12. Electric Discharge Light
Electric discharge light is produced when an electric current passes through a gas source
The electrons within the gas become excited causing them to release light.
Various gases emit different light sources

13. Where might you see various gases being used to produce light?
Christmas lights
Signs
Traffic lights
Fireworks

14. Fluorescent Light
Fluorescent lights are commonly found in school, businesses, and various other industries.
Fluorescent lights are composed of a phosphor powder coating, mercury, and a noble gas.
At each end of a fluorescent light there is an electrode.

15. Fluorescent Light (Fig 10.5)
When an electric current is applied to a fluorescent light bulb, electrons collide with mercury atoms.
The mercury will then release UV radiation (not visible) which is absorbed by the phosphor coating
The phosphor coating emits visible fluorescent light

16. Demonstration: Blacklight Applications
Ask students for cash money, tell them thank you, I have just demonstrated how easy it is to get people to give you money.
Argon is typically used as the halogen

17. Literacy Check: Fluorescent Applications
In the same group as the placemat, read page 406 (Figure 10.7)
Create a short scenario (4-5 sentences) where fluorescence may be used. Explain how fluorescence helped resolve the problem.

18. Types of Luminescence Luminescence:
Is the light produced without heating an object
Fluorescence is a type of luminescence because it does not use heat to produce light
Phosphorescence, chemiluminesence, and bioluminescence are all prime examples of luminescence.

19. 1. Phosphorescence Phosphorescence:
Is similar to fluorescent light because it uses UV light to create light
However, the major difference is that phosphorescence glows long after the UV light has been absorbed

20. 2. Chemiluminescene
Chemiluminescence is light that is generated by the energy released in a chemical reaction.

21. 3. Bioluminescence Bioluminescence is a form of chemiluminescence
Occurs where energy is released by a chemical reaction in the form of light.
Top: Firefly, Glowworm, bobtail squid Bottom: Firefly larva, fungus, Dinoflagellate

22. Homework Answers questions #1-4 (p. 407)
Notes: Question number one discuss the “excited atom”. In this lesson we have focused on the “excited electron” which is part of the atom.

23. The Nature of Light
Light is energy that travels like a wave through empty space.
Electromagnetic waves
Electromagnetic waves function as ocean waves as they have a crest and a trough

24. Light as Waves
The wavelength of light is the distance between troughs or between crests.
Electromagnetic waves are made of both a magnetic and a electric field.

25. The Electromagnetic Spectrum
Waves exist along a continuum of various wavelengths
The smaller the wavelength, the higher in energy the light
The longer the wavelength, the lower in energy is the light

26. Homework Questions
Read pages
Answer questions #1-7 (page 410)