Photoelectric Effect (How Einstein really became famous!)
Photoelectric Effect Metal Foil
Photoelectric Effect Metal Foil
Photoelectric Effect ► As blue light strikes the metal foil, the foil emits electrons.
Photoelectric Effect
► When red light hits the metal foil, the foil does not emit electrons. ► Blue light has more energy than red light. ► How could we get more energy into the red light? ► Try increasing the brightness.
Photoelectric Effect
► Well, that didn’t work! ► Maybe its still not bright enough.
Photoelectric Effect
► Still not working. ► What happens with brighter blue light?
Photoelectric Effect
► More blue light means more electrons emitted, but that doesn’t work with red.
Photoelectric Effect
► Einstein said that light travels in tiny packets called quanta. ► The energyof each quanta is given by its frequency ► The energy of each quanta is given by its frequency E=hf Energy Planck’s constant frequency
Photoelectric Effect ► Einstein stated that light interacts with matter as a stream of particle-like photons. ► Light travels as a wave, and interacts with matter as a stream of particles. ► Einstein received the Nobel Prize for this discovery.
Where do we use this? ► Solar Panels ► Solar charged calculators ► Garage door sensors ► Flash sensors on Cameras
The Dual Nature of Light
► Light is a form of energy. ► Sometimes it behaves like a particle (photons) and sometimes it behaves like a wave. ► For this reason, light is said to have a dual nature
It is the accepted concept of the nature of light.
The Dual Nature of Light ► The photoelectric effect actually combined the 2 theories of EM waves vs subatomic particles…remember the Nobel Prize? ► Why is this so important???? Quantum mechanics was created and deals with physical phenomena at the atomic level…. Quantum mechanics was created and deals with physical phenomena at the atomic level…. ► It departs from classical (Newtonian) physics primarily b/c matter behaves differently at the atomic level
The properties of light can be summarized into two groups…with its dual nature 3 "particle" properties 3 "particle" properties 1) Travels in straight lines 2) Reflection (changes direction) 3) Refraction (bends, in going from one material to another) and 3 "wave" properties 1) Interference (waves "superpose" and pass right through each other) 2) Diffraction (waves "spill over" the edges of their obstructions) 3) Polarization (eliminating one of light's "fields")
The Dual Nature of Light Particle properties of light Particle properties of light Difficult to explain using the wave theory Difficult to explain using the wave theory Wave properties of light Difficult to explain using the particle theory
State the three “wave” properties of light InterferenceDiffractionPolarization
The Dual Nature of Light State the three “particle” properties of light 1) Travels in straight lines 2) Reflection 3) Refraction
The Dual Nature of Light In your own words, define a photon. ► A photon is a packet of energy traveling at a speed of 3 x 108 m/s ► Each color is a different photon having a different amount of energy. ► A photon of red light has the least amount of energy, ► while a photon of violet light has the greatest amount of energy.
Dual Nature of Light Define light and explain what is meant by the phrase "the dual nature of light“ Light is a form of energy and has a dual nature. This means that light possesses both particle properties and wave properties.