Conceptual PhysicsConceptual PhysicsNotes on Chapter 27Notes on Chapter 27

Light

LightLight

Early Concepts of LightEarly Concepts of Light Up until the time of Newton, Up until the time of Newton,

most most scientists thought that scientists thought that light was a light was a particle. Dutch particle. Dutch scientist scientist Christian Christian Huygens Huygens said light was a wave.said light was a wave.

Then in 1905, Then in 1905, EinsteinEinstein said light was said light wassmall particles - massless bundles of small particles - massless bundles of energy that behaved like waves calledenergy that behaved like waves called photonsphotons..

LightLight Speed of LightSpeed of LightIn 1675, a Danish In 1675, a Danish astronomer named astronomer named Olaus Olaus RoemerRoemer demonstrated that demonstrated that light travels as a finite speedlight travels as a finite speed

Roemer’s Experiment pg. 405Roemer’s Experiment pg. 405

Dutch scientist Dutch scientist HuygensHuygens looked looked at Roemer’s data and calculated at Roemer’s data and calculated the speed of light to be 300,000 the speed of light to be 300,000 km/s.km/s.

LightLight In 1880, an American In 1880, an American

scientist named scientist named Albert Albert MichelsonMichelson performed a performed a experiment using a experiment using a spinning mirror to find spinning mirror to find the speed of light.the speed of light.

Michelson’s ExperimentMichelson’s Experiment

LightLight

LightLight Michelson speed for light (the Michelson speed for light (the

excepted value today) is 299,920 excepted value today) is 299,920 km/s.km/s.

NOTENOTE: We will use Roemer’s : We will use Roemer’s roundedrounded

number of 300,000 km/s.number of 300,000 km/s.

LightLightFFUN UN FFACTSACTS

Light would travel 7.5 times Light would travel 7.5 times around Earth in one second.around Earth in one second.

Light takes 8 minutes to travel Light takes 8 minutes to travel from the Sun to Earth - a distance from the Sun to Earth - a distance of 93,000,000 miles.of 93,000,000 miles.

Traveling at the speed of light, it Traveling at the speed of light, it would take 4 yrs to travel to the would take 4 yrs to travel to the nearest star.nearest star.

LightLight

ElectromagneElectromagnetic Wavestic Waves

Electromagnetic Electromagnetic SpectrumSpectrum is a is a continuous range continuous range of waves of waves extending from extending from the longest the longest (Radio) and going (Radio) and going to the shortest to the shortest (Gamma).(Gamma).

LightLight Any material that allows light to Any material that allows light to

pass through in straight lines is pass through in straight lines is said to be said to be transparenttransparent..

EX: GlassEX: Glass

WaterWater

Any material that absorbs light w/o Any material that absorbs light w/o reemission is said to be reemission is said to be opaqueopaque..

EX: WoodEX: Wood

StoneStone

LightLightSHADOWSSHADOWS

A thin beam of light is called a A thin beam of light is called a RayRay. . When light rays can not go past an When light rays can not go past an object, a shadow is formed.object, a shadow is formed.

Two parts of a shadow are:Two parts of a shadow are: umbraumbra: a total shadow.: a total shadow. penumbrapenumbra: a partial shadow.: a partial shadow.

EX: Solar and Lunar EclipsesEX: Solar and Lunar Eclipses See pg. 413 See pg. 413 Fig. 27.12 & 27.13Fig. 27.12 & 27.13

LightLightPOLARIZATIONPOLARIZATION

Light is a Light is a transversetransverse wave. wave. White light is Non-White light is Non-polarized.polarized.

When passed through a When passed through a filter (Polarizer) only lightfilter (Polarizer) only light that is moving that is moving same as thesame as the filter openingfilter opening will make it will make it through.through.

– See pg. 415See pg. 415 Fig. 27.18Fig. 27.18

LightLight