Light (simply)Light (simply)

A Simple Review for Complex Seniors

A Simple Review for Complex Seniors

EM RadiationEM 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 3x108 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 3x108 m/s

model

Sources of LightSources 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 LightQuantity 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 RelationshipInverse-Square Relationship

Luminous IntensityLuminous Intensity

The flux that falls on 1m2 of the inside of a 1 meter radius sphere.

Intensity is flux/4π and is measured in candela, (cd).

The flux that falls on 1m2 of the inside of a 1 meter radius sphere.

Intensity is flux/4π and is measured in candela, (cd).

Ray Model of LightRay 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 DualityWave-Particle Duality

Christiaan Huygens- Dutch (1629-1695) presents a “wave model of light” to explain

diffraction patterns.

Newton- English (1643-1727) presents a “corpuscle (particle) model of light”

in competition.

Christiaan Huygens- Dutch (1629-1695) presents a “wave model of light” to explain

diffraction patterns.

Newton- English (1643-1727) presents a “corpuscle (particle) model of light”

in competition.

Light as a WaveLight as a Wave

Thomas Young’s Double Slit Experiment 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 ParticleLight as a Particle

Albert EinsteinAlbert 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 EmissionColor by Emission

Bohr’s model of the atom requires “quantized” energy levels.

Bohr’s model of the atom requires “quantized” energy levels.

EnergiesEnergies

We use Hydrogen as our reference point:

Where n is a positive integer.

Which means the first 3 energy levels are :

-13.6 eV, -3.40 eV, -1.51 eV

We use Hydrogen as our reference point:

Where n is a positive integer.

Which means the first 3 energy levels are :

-13.6 eV, -3.40 eV, -1.51 eV

En =−13.6eV

n2

-13.6 eV, -3.40 eV, -1.51 eV-13.6 eV, -3.40 eV, -1.51 eV

-1.51 eV

-3.40 eV

-13.6 eV

1.89 eV

12.09 eV

10.2 eV

Spectral linesSpectral lines

Violet (380-435nm)Blue (435-500 nm)Cyan (500-520 nm)Green (520-565 nm)Yellow (565- 590 nm)Orange (590-625 nm)Red (625-740 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 =

E =hυ

υ c

λ

λ =hc

E 4.135x10−15eVgs

λ2→1 =

(4.135x10−15eVgs)(3x108m / s)

10.2eV= 1.216x10−7m

λ3→1 =

(4.135x10−15eVgs)(3x108m / s)

12.09eV= 1.026x10−7m

λ3→2 =

(4.135x10−15eVgs)(3x108m / s)

1.89eV= 6.563x10−7m

-13.6 eV, -3.40 eV, -1.51 eV-13.6 eV, -3.40 eV, -1.51 eV

-1.51 eV

-3.40 eV

-13.6 eV

656 nm (RED!)

103 nm

122 nm

Color by AbsorbtionColor 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?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?Why?

GUMMY BEARS AND LASERS!

Doppler for LightDoppler for Light

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

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

fobs = f 1±vc

⎛⎝⎜

⎞⎠⎟

λobs − λ( ) = Δλ = ±v

cλ