Placemat Activity: Different Types of Light

3. PlacematActivity: 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

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 (1962- 1982) 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.

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.

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 403-410 • Answer questions #1-7 (page 410)