4 Unit 4: Chapter 10 – Sources and Nature of Light (p.403-410) ArtificialGenetically modified zebrafish emit visible light when exposed to UV radiation.NaturalAlgae and bacteria are able to emit light naturallyBioluminescence
6 What is light?Light is a form of energy known as electromagnetic wavesWhen 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 ABSORBEDE.g. Chlorophyll is green because it does not absorb green lightTextbook refers to excited atoms not electrons
7 Types of Light Emissions There are three types of light emissions:Light from the sunLight from incandescentLight from electric discharge
8 Sun lightHydrogen atoms in the Sun’s core are moving at rapid speeds and colliding with one anotherThese collisions will sometimes cause two Hydrogen's to fuse together forming Helium.A fusion reactionThis reaction releases a ton of energy creating light.
9 SunlightSunlight emits white light which is made up of all light colours.
10 Incandescent LightIncandescent light occurs when a metal is heated to produce lightTungsten wire is typically used because of its brightness when heatedIt 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 sourceThe 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 lightsSignsTraffic lightsFireworks
14 Fluorescent LightFluorescent 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 coatingThe 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 objectFluorescence is a type of luminescence because it does not use heat to produce lightPhosphorescence, 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 lightHowever, the major difference is that phosphorescence glows long after the UV light has been absorbed
20 2. ChemiluminesceneChemiluminescence 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 LightLight is energy that travels like a wave through empty space.Electromagnetic wavesElectromagnetic waves function as ocean waves as they have a crest and a trough
24 Light as WavesThe 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 wavelengthsThe smaller the wavelength, the higher in energy the lightThe longer the wavelength, the lower in energy is the light