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Planck's hypothesis

Blackbody Radiation

Theory: Intense radiation can not be infinite

Reasoning: True intensity, all objects cannot emit infinite radiation

Result: Ultraviolet Catastrophe

Plancks Solution: Energy in a blackbody comes in discrete parcels

  • A blackbody is an object that absorbs radiation ex; oven
  • The radiation they emit is known as blackbody radiation
  • This radiation is emitted over a spectrum

KAHOOT TIME

Example 2

Photons Possess Energy and Momentum

Photon Interactions

Einstein's quantum theory states that light energy can only be absorbed or emitted in discrete parcels

A certain AM radio station has frequency near 1.0 MHz, and a certain Fm station has frequency near 110MHz . Radio waves produce photons

Compare the momentum of the photons from the AM station with the momentum of the photons from the FM station.

Facts Michael won

P(photon) = hf / c

Photon energy

Photon reflection

Electron absorption

Less energy and lower frequency of photon

Absorption of photon

Pair creation

We can use the equation E(photon) = hf to calculate the energy carried by a single photon

Einstein's Theory of Light

Einstein proposed that photons carry parcels of kinetic energy

where f is Planck’s constant

E = hf

The threshold frequency in the photoelectric effect corresponds to photons whose energy is equal to work

hf = W

Ek = hf - W

Wien's Law

Wien's Law is used to determine the wavelength at the maximum radiation intensity of a blackbody

Photoelectric Effect

Einstein’s contribution to the theory of light

Einstein proposed that light is a collection of particles known as photons

- Electrons can be extracted from metal by shining light onto it

- These electrons are ejected at a frequency known as threshold frequency

- This disproved wave theory

Why are Photons not the same as particles?

FUN FACT

Einstein won the Nobel prize for Physics in 1921for his contributions regarding photoelectric effect

Example 1

Aluminum is being used in a photoelectric effect experiment. The work function of aluminum is 6.73 x 10^-19 J

Calculate the minimum photon energy and frequency needed to emit electrons

Equations to keep in mind

V = f X wavelength

f = c / wavelength

f = E(photon) / h

Because they do not have any mass and they exhibit interference effects

Wave - Particle Nature of Light

What are we going to be Learning ?

The work function

~ To understand Blackbody Radiation and the photoelectric effect , we assume light to be made of particles

~ However due to properties such as interference, light is also considered a wave

The Theory of light

~ By the 1800’s, physicists believed that light acts as an electromagnetic wave

~ However this was only according to CLASSICAL physics

~ As more studies were conducted, more discoveries were made suggesting that light is made of BOTH particles and waves

- Metal contains electrons that are free to move around within metal but are still bound as a whole to the metal

- This is because of their attraction to the +ive charges of the metal at the metal atom nuclei

Work Function

Today we will be learning about light, the behaviour of it as well as the properties of it.

- Work's value is in electron-volts (eV)

- To convert electrons-volts to joules this is the conversion factor :

1eV = 1.60 X 10^-19 J

W = e V

e is the elementary charge

V is the electric potential difference

- The minimum energy required to remove a single electron from a piece of metal is called the Work Function

12.2

Photons and the Quantum Theory of Light

By: Abdul-Rahman Shahzad & Moiz Ahmed

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