Photoelectric Effect

Photoelectric EffectPhotoelectric Effect

(How Einstein really became (How Einstein really became famous!)famous!)


Metal Foil


►As blue light strikes the metal foil, the As blue light strikes the metal foil, the foil emits electrons.foil emits electrons.


►When red light hits the metal foil, the When red light hits the metal foil, the foil does not emit electrons.foil does not emit electrons.

►Blue light has more energy than red Blue light has more energy than red light.light.

►How could we get more energy into How could we get more energy into the red light?the red light?

►Try increasing the brightness.Try increasing the brightness.


►Well, that didn’t work!Well, that didn’t work!►Maybe its still not bright enough.Maybe its still not bright enough.


►Still not working.Still not working.►What happens with brighter blue light?What happens with brighter blue light?


►More blue light means more electrons More blue light means more electrons emitted, but that doesn’t work with emitted, but that doesn’t work with redred..


►Einstein said that light travels in tiny Einstein said that light travels in tiny packets called packets called quanta.quanta.

►The energyThe energy of each quanta is given by of each quanta is given by its frequencyits frequency

E=hfE=hfEnergyEnergy

Planck’s constantPlanck’s constant

frequencyfrequency


►Einstein stated that light interacts with Einstein stated that light interacts with matter as a stream of particle-like matter as a stream of particle-like photons.photons.

►Light travels as a wave, and interacts Light travels as a wave, and interacts with matter as a stream of particles.with matter as a stream of particles.

►Einstein received the Nobel Prize for Einstein received the Nobel Prize for this discovery.this discovery.

Where do we use this?Where do we use this?

►Solar Panels Solar Panels ►Solar charged calculatorsSolar charged calculators►Garage door sensorsGarage door sensors►Flash sensors on CamerasFlash sensors on Cameras

The Dual Nature of LightThe Dual Nature of Light


►Light is a form of energy. Light is a form of energy.

►Sometimes it behaves like a Sometimes it behaves like a particle particle (photons) and sometimes it behaves like (photons) and sometimes it behaves like aa wave wave . .

► For this reason, For this reason, light is said to have a dual light is said to have a dual naturenature

It is the accepted concept of the It is the accepted concept of the nature of light.nature of light.


► The photoelectric effect actually combined the 2 The photoelectric effect actually combined the 2 theories of EM waves vs subatomic particles…theories of EM waves vs subatomic particles…remember the Nobel Prize?remember the Nobel Prize?

► Why is this so important????Why is this so important????

Quantum mechanicsQuantum mechanics was created and deals was created and deals with physical phenomena at the atomic level….with physical phenomena at the atomic level….

► It departs from classical (Newtonian) It departs from classical (Newtonian) physics primarily b/c physics primarily b/c matter behaves differently at matter behaves differently at the atomic levelthe atomic level

The properties of light can be The properties of light can be summarized into two groups…with summarized into two groups…with

its dual natureits dual nature 3 "particle" properties3 "particle" properties

1) Travels in straight lines1) Travels in straight lines

2) Reflection (changes 2) Reflection (changes direction)direction)

3) Refraction (bends, in 3) Refraction (bends, in going from one material to going from one material to another) another)

and 3 "wave" propertiesand 3 "wave" properties

1) Interference (waves 1) Interference (waves

"superpose" and pass right "superpose" and pass right through each other) through each other)

2) Diffraction (waves "spill 2) Diffraction (waves "spill over" the edges of their over" the edges of their obstructions) obstructions)

3) Polarization (eliminating 3) Polarization (eliminating one of light's "fields") one of light's "fields")

The Dual Nature of LightThe Dual Nature of Light Particle properties of Particle properties of

lightlight

Difficult to explain using Difficult to explain using the wave theorythe wave theory

Wave properties of Wave properties of lightlight

Difficult to explain using Difficult to explain using the particle theorythe particle theory

State the three “wave” properties of lightState the three “wave” properties of light

InterferenceInterference

DiffractionDiffraction

PolarizationPolarization


State the three “particle” properties of lightState the three “particle” properties of light

1) Travels in straight lines1) Travels in straight lines

2) Reflection2) Reflection

3) Refraction3) Refraction


In your own words, define a photon.In your own words, define a photon.

►A photon is a packet of energy traveling at a speed A photon is a packet of energy traveling at a speed of 3 x 108 m/sof 3 x 108 m/s►Each color is a different photon having a different Each color is a different photon having a different amount of energy. amount of energy. ► A photon of red light has the least amount of energy,A photon of red light has the least amount of energy,►while a photon of violet light has the greatest amount while a photon of violet light has the greatest amount of energy.of energy.

Dual Nature of LightDual Nature of Light

Define light and explain what is meant by the Define light and explain what is meant by the phrasephrase

"the dual nature of light“"the dual nature of light“

Light is a form of energy and has a dual Light is a form of energy and has a dual nature. This means that light possesses both nature. This means that light possesses both

particle properties and wave properties. particle properties and wave properties.

Photoelectric Effect

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