# Unit Planner: Quantum and nuclear physics

Unit: Quantum and nuclear physics

Start date:

**Diploma assessment**

*When will the content be assessed?*

*x Paper 1x Paper 2Paper 3x Investigation*

**Text book reference**

Hamper

#### Inquiry: Establishing the purpose of the unit

**Transfer Goals***List here one to three big, overarching, long-term goals for this unit. Transfer goals are the major goals that ask students to “transfer”, or apply, their knowledge, skills, and concepts at the end of the unit under new/different circumstances, and on their own without scaffolding from the teacher. *

- To know that the photoelectric effect provides evidence for the quantum nature of light, and the implications of the wave nature of matter
- To understand the quantitative significance of the random nature of radioactive decay
- To be able to suggest the products of nuclear reactions based on conservation of quantities

**Content***List here the key content that students will know by the end of the unit.*

__Photoelectric effect__

- Revise atomic models and electron energy levels.
- Describe the photoelectric effect.

__Wave nature of matter__

- Accept that a photon can collide with an electron and when this happens the photon is behaving like a particle (waves don't collide).
- Describe the two slit experiment for electrons.
- Introduce the concept of Heisenberg's uncertainty principle in relation to momentum and position.

__Atomic models__

- Outline Schrodingers model.
- Mass energy equivalence. Particle - antiparticle annihilation and pair production
- Introduce the concept of spin.

__Exponential decay__

- Accept that nuclear decay is a random process and that the probability of decay is related to the amount of energy that will be released when it happens.

**Skills***List here the key skills that students will develop by the end of the unit. *

__Photoelectric effect__

- Understand how discrete energy levels leads to the idea that light is made of photons.
- Understand the difference between photons and continuous light waves.
- Understand why the wave model does not explain the photoelectric effect and how it can be explained with the quantum model.

__Wave nature of matter__

- Understand why large particles do not exhibit wave properties.
- Understand the relationship between the wave and the probability of an interaction.
- Use the passage of electrons through a narrow opening to show how decreasing the uncertainty in position leads to an increase in the uncertainty in momentum.
- Having accepted that electrons have wave like properties, apply what we know about standing waves to model atomic electrons.

__Atomic models__

- Understand how the Bohr model predicts the Hydrogen spectrum by applying the equations for circular motion for orbits that have quantised angular momentum.
- Understand how the electron in a box model predicts discrete energy levels.
- Electron tunneling as a consequence of quantum mechanics.

__Exponential decay__

- Understand that the number of decays per second in a sample of material is directly proportional to the number of nuclei.
- Understand how half life gives a measure of the rate of decay of a sample.
- Understand why the activity is also exponential and that the activity is more useful to us than the number of particles.

**Concepts***List here the key concepts that students will understand by the end of the unit.*

__Photoelectric effect__

- Interpret the results of Milikan's experiment.
- Use Einstein's equation to solve problems.

__Wave nature of matter__

- Understand why large particles do not exhibit wave properties.
- Understand the relationship between the wave and the probability of an interaction.
- Use the passage of electrons through a narrow opening to show how decreasing the uncertainty in position leads to an increase in the uncertainty in momentum.

__Exponential decay__

- See that if dN/dt ∝ N, then the decay is exponential.

**Applications***Examples of real world practical applications of knowledge. *

__Photoelectric effect__

- Electricity generation by photovoltaic cells.

__Wave nature of matter__

- Electron diffraction for observation at atomic scale.

__Atomic models__

- Students taking chemistry will recognise the quantum numbers mentioned here.

__Exponential decay__

- The decay of radioactive
^{14}C can be used to find the age of dead organic matter.

#### Action: teaching and learning through Inquiry

**Approaches to teaching***Tick boxes to indicate pedagogical approaches used. *

*x Lecture*

x Simulation

x Small group work (pairs)

x Hands on practical

x Video

x Simulation

x Small group work (pairs)

x Hands on practical

x Video

**TOK***Examples of how TOK can be introduced in this unit *

__Photoelectric effect__

- The scientific method: We use the wave model to explain diffraction and interference effects of light but it can not explain the photoelectric effect so we have to modify the model.
- Are photons really a packet of waves or is this just the way we describe them?
- Simulations like PhET help us to understand phenomena like the photoelectric effect, sometimes revealing unexpected results, but do they model the real situation?

__Wave nature of matter__

- How can an electron be a particle and a wave? The use of models in physics.
- Should we imagine the appearance of moving red balls and water waves in space when writing equations for waves?
- We can never observe the wave properties of a tennis ball; does this mean it doesn't have an associated wave?
- Determinism: if we knew the position and momentum of all particles in the universe we could use the equations of motion to calculate their position at any time in the future. However according to Heisenberg we can not know the position and momentum of a single particle so we can not predict the future.
- Heisenberg is not about measurement; it's about the way things are. This always leads to some discussion.

__Atomic models__

- If quantum mechanics applied to us then we could suddenly find ourselves outside the classroom without having gone through the door.

__Exponential decay__

- When dealing with the random nature of radioactive decay one could bring up Schroedinger's cat, but I tend to leave him out at this stage, preferring not to let the cat out of the bag too early.

**NOS***Examples of how NOS can be introduced in this unit. *

__Photoelectric effect__

- Diffraction of light shows that light has wave like properties but the wave model cannot explain the experimental results of the photoelectric effect. A new model has to be derived which combines the properties of particle and waves (wave quanta).
- Try to predict the results of Milikan's experiment using wave theory. This gives the wrong result so the theory needs to be modified. The new model has to also fit in with existing explanations, hence wave-particle duality.

__Wave nature of matter__

- The reverse of the photoelectric effect. You can't explain the diffraction of electrons by crystals by considering electrons as particles, so have to modify the model.
- The way Heisenberg's uncertainty principle gives the correct size of an atom is an example of how different theories must lead to the same predictions.

__Atomic models__

- In 1921 the Stern Gerlach experiment showed that electrons had spin +1/2 or - 1/2. In 1928 Dirac used a relativistic approach to modify the Schrodinger equation to include spin.

**Assessments***Tests, exams and marked labs*

- MCQs: Photoelectric
- Problems: Photoelectric Effect
- Test: Wave nature of matter
- MCQs: Wave particle duality
- Problems: Wave particle duality
- Test: Further atomic models
- Problems: Atomic Models
- Test: Radioactive decay
- Practical: Measuring half life of beer foam
- MCQs: Nuclear mass and exp decay
- MCQs: Exponential decay
- Problems: Nuclear AHL

**Worksheets and exercises**

**Resources***Video clips, simulations demonstrations etc*.

#### Reflections

**What went well***List the portions of the unit (content, assessment, planning) that were successful *

**What didn’t work well***List the portions of the unit (content, assessment, planning) that were not as successful as hoped *

**Notes/changes/suggestions:***List any notes, suggestions, or considerations for the future teaching of this unit *