1. G482 Electrons , Photons and Waves - Quantum Physics

2. Quantum Physics Energy of a photon The photoelectric effect
Wave–particle duality
Energy levels in atoms

3. Energy of a Photon What is a Photon ?
a quantum/packet/of electromagnetic energy

4. Energy of a Photon
How do you calculate the energy of a photon ?

5. The Photoelectric Effect
Describe the Photoelectric Effect
A photon is absorbed by an electron in a metal surface causing an electron to be emitted.
Energy of photon = hf
Energy is conserved.
Only electrons with energy above the work function energy will be emitted.
Only light with a frequency greater than the threshold frequency will cause emission
Energy=work function + Max KE of electron.
The work function is the minimum energy required to release an electron from the surface.
Number of electrons emitted depends on light intensity.
( Energy of Electron does not)

6. The Photoelectric Effect
Describe the Photoelectric Effect Experiment
A clean zinc plate is mounted on the cap of a gold leaf electroscope where the plate is initially charged negatively .
Shine a UV light on the plate and watch the gold leaf collapse as charge leaves the plate, indicating the emission of electrons

7. The Photoelectric Effect
Photoelectric Effect Graphical Analysis

8. The Photoelectric Effect
Photoelectric Effect Graphical Analysis
As intensity goes up more electrons emitted
As frequency goes up it does not affect the number of electrons emitted
As intensity goes up it does not affect the energy of the electrons.

9. The Photoelectric Effect
Photoelectric Effect Numerical Analysis
To convert from eV to J multiply by 1.6 x

10. The Photoelectric Effect
Describe the LED Experiment to find h
Adjust the potential divider to low/zero voltage
Connect flying lead to one LED
Increase voltage until LED just lights/strikes
Repeat several times and average to find Vmin
Repeat for each LED
Shield LED inside opaque tube to judge light more accurately

11. Wave Particle Duality When do waves behave like particles ?
In the photoelectric effect – the energy of the light does not depend on the amplitude of the wave but on its frequency.

12. Wave Particle Duality When do particles behave like waves ?
Travelling electrons are diffracted by graphite producing a series of diffraction rings. Maximum diffraction occurs when the de Broglie wavelength of the electrons is similar to the gap between layers of carbon atoms.

13. Wave Particle Duality
What is the de Broglie wavelength for an electron ?
Travelling electrons are observed to behave as waves/show wavelike properties
Where the electron wavelength depends on its speed/momentum

14. Energy Levels in Atoms What is an Emission Line Spectrum?
light emitted from excited isolated atoms produces a line spectrum
a series of sharp/bright/coloured lines
against a dark background

15. Energy Levels in Atoms What is an Absorption Line Spectrum?
in an absorption spectrum a series of dark lines appears against a bright background/within a continuous spectrum

16. Energy Levels in Atoms Why are spectra important?
They reveal that electrons within atoms can only occupy certain energy levels.

17. Explaining Line Spectra

18. Energy Levels in Atoms Numerical and Graphical Analysis
An energy-level diagram for the hydrogen atom
Numerical and Graphical Analysis
Electrons have discrete energy levels within atoms - they cannot have any energy .
hf or hc/λ = E1 – E2