WAVE PARTICLE DUALITY

Principles of Physics

Is light a wave or a particle?? Isaac Newton said light is a particle Christian Huygens (explained diffraction) said

light is a wave Thomas Young (proved light diffracts and

interferes) said light is a wave James Clerk Maxwell (related electricity and

magnetism through a set of complex equations) said light is electromagnetic radiation (wave) Hertz (produced radio waves) supported Maxwell

Einstein said light is a particle

Einstein’s Particle theory

Light is made up of concentrated bundles of electromagnetic energy, which are also called quanta of electromagnetic energy

Quantum

An elemental unit Smallest amount of something Plural = quanta

Example: Money – Each denomination is a whole number multiple of the smallest

Smallest denomination: penny1 dollar = 100 pennies1 quarter = 25 pennies

Quantum Example

Mass of a pure gold ring = whole number multiple of the mass of a gold atom

Therefore, gold is quantized In fact, all matter is quantized

Photons

A quantum of light is called a photon Photons move at one speed:

300,000,000 m/s Light is not emitted continuously

Instead it is a stream of photons each with its own energy

Photoelectric Effect

Proof of the existence of photons Einstein won the Nobel Prize for this

Electrons can be ejected from certain materials when light shines on them Energy is transferred from the photon to an

electron

Photoelectric Effect

•Higher frequency allows the ejected electrons to have more energy when they leave

•Higher amplitude (brighter) light allows more electrons to be ejected, but has nothing to do with the energy of the individual electrons

Photoelectric Effect

Photoelectric Effect - Light, Quantum Mechanics, Photons - PhET

Uses of Photoelectric Effect

Solar power Photons eject electrons from photosensitive

materials. The electrons collect and flow in wires creating a current)

Electric eyes (they can be used to open doors automatically) A beam of light shines across an opening to

a detector. The beam of light maintains a current until it is blocked by you coming to the door. When the detector senses the change in current it open the door.

Wave Model vs Particle Model

WaveParticle

1. Reflection _______ _______

2. Refraction _______ _______

3. Diffraction _______ _______

4. Interference _______ _______

5. Photoelectric Effect _______ _______

X X

X X

X

X

X

Particles as Waves

All matter and energy have both wavelike and particle-like properties Wavelike properties of matter are not

normally seen unless you look at very fine details

Ordinary-size objects have wavelengths that are much too small to be measured. Therefore, a batter does not have to worry about the wavelength of a baseball.