Placemat Activity: Different Types of Light

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

Bioluminescence

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

Types of Light Emissions• There are three types of light emissions:

– Light from the sun

– Light from incandescent

– Light from electric discharge

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.

Sunlight• Sunlight emits white light which is made up of

all light colours.

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

Incandescent Demonstration Copper Penny

• Why might an older penny (1962- 1982) be more effective at producing light when heated?

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

Where might you see various gases being

used to produce light?

Christmas lightsSigns

Traffic lights Fireworks

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.

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

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.

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.

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.

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

2. Chemiluminescene• Chemiluminescence is light that is generated

by the energy released in a chemical reaction.

3. Bioluminescence• Bioluminescence is a form of chemiluminescence– Occurs where energy is released by a chemical

reaction in the form of light.

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.

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

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.

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

Homework Questions

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