What is Light?What is Light?

Fill in the blanks on the handout. Anything written like this must go on your handout

Visible light is one of the many forms of Visible light is one of the many forms of electromagnetic radiation. It is created electromagnetic radiation. It is created primarily in the sun, but is also emitted by primarily in the sun, but is also emitted by electrons in atoms. Furthermore, light is electrons in atoms. Furthermore, light is ENERGY! And this energy travels in ENERGY! And this energy travels in waves!waves!

Properties of WavesProperties of Waves

Rest position

Crest: highest point in a wave

Trough: lowest point in a wave

Rest position: when there are no waves

Draw this diagram!

Wavelength Wavelength Distance between peaks on a waveDistance between peaks on a wave

AmplitudeAmplitudeWave height (from the rest position to the Wave height (from the rest position to the

crest)crest)The larger the amplitude, the more energy The larger the amplitude, the more energy

FrequencyFrequencyRate of repetition of a waveRate of repetition of a waveThe higher the frequency, the more energy The higher the frequency, the more energy

Rest position

**The energy of a wave depends on its **The energy of a wave depends on its amplitude and frequency amplitude and frequency BUT, the higher the frequency, the shorter the BUT, the higher the frequency, the shorter the

wavelengthwavelengthThese waves are called These waves are called electromagnetic electromagnetic

waveswaves and the types of electromagnetic and the types of electromagnetic waves make up what is called the waves make up what is called the electromagnetic spectrum!electromagnetic spectrum!

The Electromagnetic SpectrumThe Electromagnetic Spectrum

Light passage through materialsLight passage through materials

Light may be absorbed, reflected, or Light may be absorbed, reflected, or transmittedtransmittedOpaque:Opaque: do not transmit light, eg. rock do not transmit light, eg. rockTransparent:Transparent: transmit light, eg. glass transmit light, eg. glassTranslucent:Translucent: transmit some light, eg. Frosted transmit some light, eg. Frosted

glassglassLight may also be reflected or refractedLight may also be reflected or refracted

Light moves in a straight lineLight moves in a straight line

Evidence:Evidence: If you line up sheets of paper with If you line up sheets of paper with a pinhole in each of them, light will travel a pinhole in each of them, light will travel throughthrough Move the pinhole and no light will pass throughMove the pinhole and no light will pass through

ShadowsShadows

Objects block light from reaching from Objects block light from reaching from reaching an area the same shape of the reaching an area the same shape of the object, causing it to appear black object, causing it to appear black

SunSUN

EclipsesEclipses

Solar Eclipse:Solar Eclipse: Moon blocks light from the sunMoon blocks light from the sun

So if you stand anywhere here, you cannot see the sun!

Solar EclipseSolar Eclipse

EclipsesEclipses

Lunar Eclipse:Lunar Eclipse: Earth blocks light from the Earth blocks light from the moonmoon

The moon will appear completely black since it is getting no light!

Lunar EclipseLunar Eclipse

LuminescenceLuminescence

Chemiluminescence:Chemiluminescence: light released light released during a chemical reaction, eg. Glowsticksduring a chemical reaction, eg. Glowsticks

Bioluminescence:Bioluminescence: light released from light released from living creatures eg. Firefliesliving creatures eg. Fireflies

Fluorescence:Fluorescence: ultraviolet light activating a ultraviolet light activating a substance called a phosphor, which substance called a phosphor, which releases energy as lightreleases energy as light

Coral fluorescent under UV lightPolyethylene microspheres

Practical ApplicationsPractical Applications

Detecting counterfeit moneyDetecting counterfeit money

Sunblock protects from UV raysSunblock protects from UV rays

Security markers/stampsSecurity markers/stamps