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For discovering the Law of the photoelectric effect.

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Isaac Newton
“Light is a not a wave, but made of particles called a corpuscles (small discreet particles as different parts of light”.

Discovered the spectrum of VIS light, as it disperses through a prism.

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Dutch physicist and astronomer famous for WAVE THEORY OF LIGHT.

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EM Wave Theory of light.

Discovered the connection between light electromagnetic waves.
Light consists of:
An electric field
A magnetic field

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...and there was light

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“The exchange of energy between light and matter only occurs in discrete amounts, called quanta.”

Planck constant, h = 6,62 ×10⁻³⁴ J

h is the quantum of electromagnetic action, which relates the energy carried by a photon to its frequency.

A photon's energy is equal to its frequency multiplied by the Planck constant.  E = hf

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Energy of a photon is always a “multiple” of h, depending on the frequency of light

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Energy of a photon is always a “multiple” of h, depending on the frequency of light

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Energy is quantized - Read this book to understand 

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Energy is quantized - Read this book to understand 

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Read to you last year in class :-)

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Young’s Double slit experiment

Light has wave-particle duality.

It can act as particle or wave.

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Classroom Aid - Young Double Slit Experiment

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https://www.sciencelearn.org.nz/videos/51-the-photoelectric-effect

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Frequency = The number of complete waves that pass a point per second. (measured in hertz, Hz).

Wavelength = The distance between two consecutive points on a wave that are in phase. (measured in metres, m)

Photoelectric effect = The process that occurs when electromagnetic radiation shines on a certain metal surface and it ejects electrons from the metal.

Photon = The quantum of energy when the energy is in the form of electromagnetic radiation.

Threshold frequency (f₀) = The minimum frequency of radiation at which electrons will be ejected from the surface of a certain metal.

Work function (W₀) = The minimum energy needed to emit an electron from the surface of a certain metal.

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E k = hf - W ₀
Ek= hf - φ

Or:
1/2mv ² = hf - hf ₀

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ANALOGY FOR WORK FUNCTION AND THRESHOLD FREQUENCY - A ROCKET LAUNCH! Escape velocity & Launch energy

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ANALOGY FOR WORK FUNCTION AND THRESHOLD FREQUENCY - A ROCKET LAUNCH! Escape velocity & Launch energy

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Efuel = Ek + E needed to overcome weight

Fnet = Ffuel - Fg
Enet = Efuel - E to overcome weight
Ek     = Efuel - EFg

The same happens with electrons in a metal surface when light falls onto it.

If the light is of sufficient energy, then the electrons can be ejected off the particular metal surface.

This is called the photoelectric effect.

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Effect of wavelength of the incident photons on the kinetic energy of the ejected photoelectrons:

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Effect of wavelength of the incident photons on the kinetic energy of the ejected photoelectrons:

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Recall:
v = fλ
So, for lightwaves:
c = fλ
f = c/λ

The energy of the photons:
E = hf
= hc/λ

E ∝ f
E ∝ 1/λ

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Figuring out: Will electrons be ejected?

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Figuring out: Will electrons be ejected?

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Photoelectric Effect - Will electrons be ejected from the metal? (From Wavelength)

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You must Explain its working

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How can photons act as particles if they are massless?

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How can photons act as particles if they are massless?

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Photons = packets (quanta) of light

Photons are massless; m = 0

So how can they act as particles (as if they have mass)?
• Photons have MOMENTUM due to Energy, and can impart their energy to electrons of any metal surface to eject them off of the surface.
• Mass of a photon comes from its energy divided by the speed of light squared:
• m photon = hf/c ²

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Particle Physics (21 of 41) What is a Photon? 5. Photon Mass (or No Mass)

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One electron is ejected per every one photon!

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One electron is ejected per every one photon!

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You need to be able to:

Draw a graph from relevant data.

Read off/determine the x-intercept.

Extrapolate the graph.

Read off/determine the y-intercept.

Calculate the gradient.

Interpret what gradient represents.