Light (simply) A Simple Review for Complex Seniors

EM Radiation  Light is caused by high energy electrons that move from higher energy shells to lower energy shells. The bundle of energy that they give off is called a “photon”.  Photons travel through a vacuum at 3x10 8 m/s  Light is caused by high energy electrons that move from higher energy shells to lower energy shells. The bundle of energy that they give off is called a “photon”.  Photons travel through a vacuum at 3x10 8 m/s model

Sources of Light  Luminous sources are objects that emit light waves. The sun is a luminous body.  Illuminated objects reflect or transmit light that is incident upon them. The Moon is an illuminated body.  Transparent - transmits light  Translucent - transmit, but reflects some light.  Opaque - reflects all light  Luminous sources are objects that emit light waves. The sun is a luminous body.  Illuminated objects reflect or transmit light that is incident upon them. The Moon is an illuminated body.  Transparent - transmits light  Translucent - transmit, but reflects some light.  Opaque - reflects all light

Quantity of Light  The rate at which energy is emitted from a luminous body is called the luminous flux. (P)  Measured in lumen. (lm)  A 100W light bulb emits 1750 lumen.  The rate at which energy is emitted from a luminous body is called the luminous flux. (P)  Measured in lumen. (lm)  A 100W light bulb emits 1750 lumen.

Inverse-Square Relationship

Luminous Intensity  The flux that falls on 1m 2 of the inside of a 1 meter radius sphere.  Intensity is flux/4π and is measured in candela, (cd).  The flux that falls on 1m 2 of the inside of a 1 meter radius sphere.  Intensity is flux/4π and is measured in candela, (cd).

Ray Model of Light  These photons travel in straight line paths.  Used to demonstrate the ways that light interacts with other objects.  These photons travel in straight line paths.  Used to demonstrate the ways that light interacts with other objects.

Wave-Particle Duality  Christiaan Huygens- Dutch ( )  presents a “wave model of light” to explain diffraction patterns.  Newton- English ( )  presents a “corpuscle (particle) model of light” in competition.  Christiaan Huygens- Dutch ( )  presents a “wave model of light” to explain diffraction patterns.  Newton- English ( )  presents a “corpuscle (particle) model of light” in competition.

Light as a Wave  Thomas Young’s Double Slit Experiment

 James Maxwell: studied other electromagnetic waves:  Suggested light was an EM wave  Results confirmed.  James Maxwell: studied other electromagnetic waves:  Suggested light was an EM wave  Results confirmed.

Light as a Particle

Albert Einstein  Wins Nobel prize for explaining that light is a particle AND a wave at the same time.  States that light is carried in packets of different energies.  Called quanta.  Blue has more energy than red no matter the intensity.  Why electrons are ejected for blue but not red.  Wins Nobel prize for explaining that light is a particle AND a wave at the same time.  States that light is carried in packets of different energies.  Called quanta.  Blue has more energy than red no matter the intensity.  Why electrons are ejected for blue but not red.

Color by Emission  Bohr’s model of the atom requires “quantized” energy levels.

Energies  We use Hydrogen as our reference point: Where n is a positive integer. Which means the first 3 energy levels are : eV, eV, eV  We use Hydrogen as our reference point: Where n is a positive integer. Which means the first 3 energy levels are : eV, eV, eV

-1.51 eV eV eV 1.89 eV eV 10.2 eV

Spectral lines Violet ( nm) Blue ( nm) Cyan ( nm) Green ( nm) Yellow ( nm) Orange ( nm) Red ( nm)

 The Energy of a photon is equal to Planck’s Constant times the frequency of the photon.  Frequency ( ) = measured in Hz =  So: h =  The Energy of a photon is equal to Planck’s Constant times the frequency of the photon.  Frequency ( ) = measured in Hz =  So: h =

-13.6 eV, eV, eV eV eV eV 656 nm (RED!) 103 nm 122 nm

Color by Absorbtion  Color works by absorption or reflection of specific wavelengths of light.  Green objects reflect green light and absorb all others. Magenta objects absorb all green and reflect blue and red.  Color works by absorption or reflection of specific wavelengths of light.  Green objects reflect green light and absorb all others. Magenta objects absorb all green and reflect blue and red.

How about the weird stuff?  Shine red light on a green object. What do you see?  A.) red.  B.) green  C.) orangey greenish  D.) black  Shine red light on a green object. What do you see?  A.) red.  B.) green  C.) orangey greenish  D.) black

Why? GUMMY BEARS AND LASERS!

Doppler for Light  The observed frequency is based on the relative speed between the source and the observer. (plus if toward, minus if away)