# Unit Planner: Wave phenomena

Unit: Wave phenomena

Start date:

**Diploma assessment**

*When will the content be assessed?*

*x Paper 1x Paper 2Paper 3Investigation*

**Text book reference**

Hamper 177 - 200

#### 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. *

- The frequency of a wave changes when there is relative motion between source and observer. Used in astro physics.
- Waves diffract when the pass through openings about the size of λ.
- Limits of resolution is a consequence of diffraction.

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

__Doppler__

- Experience the Doppler effect eeeeeeoowwwwwwwww.
- Derive the equations for Doppler effect with source moving towards and away from observer.
- Derive the equations for the Doppler effect for observer moving towards and away from the source.
- See how a shock wave is created.

__Diffraction__

- Introduce Huygens' construction for the propagation of waves.
- Show how the single slit diffraction pattern is obtained by adding wavelets.
- Use a simple method to derive the formula bsinθ=λ for the angular position of the first minima.

__Resolution__

- Realise that a consequence of diffraction is that it will make images of point objects impossible to resolve.
- State the Rayleigh criterion for resolution.

__Interference__

- See how the difference in path of waves from two sources leads to interference fringes.
- Use the small angle approximation to derive the equation s = λD/d.
- See how a diffraction grating can be used to produce interference fringes.
- Derive the equation dsinθ = nλ
- See how increasing the number of slits in a grating affects the sharpness of peaks leading to better resolution.
- Derive the equation for constructive and destructive interference.
- Explain the formation of coloured fringes in soap films.

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

__Doppler__

- Solve problems involving the Doppler effect.
- Use the equation for Doppler shift of light.

__Diffraction__

- Producing a diffraction pattern using laser light.
- Use GeoGebra to simulate single slit and multi slit diffraction.

__Resolution__

- Use the Rayleigh criterion to calculate the minimum distance that two points can be resolved for a given aperture.

__Interference__

- Use a laser to produce interference fringes from a double slit.
- Construct a diagram to show the path difference between waves from two sources.

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

__Doppler__

- Understand why movement of the medium has no effect on the frequency.
- Understand why the velocity of a wave will be greater when an observer moves towards the source.
- Understand why the wavelength will be shorter when a wave source moves towards an observer.

__Diffraction__

- Understand how Huygens' implies diffraction

__Resolution__

- Understand that light passing through an aperture will diffract causing a point object to become a spot.
- Understand how diffraction limits the resolving power of optical instruments so to improve resolution must use large apertures or short wavelengths.

__Interference__

- Understand the relationship between path difference and phase difference.
- Understand the effect of diffraction on two slit interference.
- Understand how increasing the number of slits in a grating affects the sharpness of peaks leading to better resolution.
- Understand how two coherent sources can be created by reflection off a thin film.
- Use analogy with waves in a string to deduce that there will be a phase change on reflection off a more dense medium.
- Account for change of wavelength with varying refractive index.

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

__Doppler__

- Speed trap (not all speed traps use Doppler shift, the laser variety works on the time between reflected pulses).
- Blood Ultra sound The examiners favourite, used to measure blood flow rate by reflecting ultrasound off the blood cells.
- Red shift is used to determine the velocity of stars and galaxies.

__Resolution__

- When constructing a high power telescope there is no point in having a large magnification without high resolution. Telescopes also have large apertures to increase the amount of light captured.
- Radio telescopes use long wavelength so need very large "apertures".
- Bluray uses a blue laser to increase resolution.
- The effect of diffraction is not the only thing that limits resolution, pixel size for example.

__Interference__

- Thin film interference is used to minimise the reflection off lenses. Doing this increases the amount of light entering the camera. This is also used in photovoltaic cells.

#### 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

Video

x Simulation

x Small group work (pairs)

x Hands on practical

Video

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

__Doppler__

- When talking about flying faster than the speed of sound you could mention Chuck Jeger and all those test pilots who risked (and some lost) their lives trying to advance technology.
- Most people will have experienced Doppler with a moving source but not a moving observer, does this make the latter more difficult to understand?

__Diffraction__

- The rotating rods in the interactive physics simulation below have nothing to do with light but help us to understand how the pattern is formed.

__Resolution__

- At various times claims have been made about the ability to read news print from an orbiting satellite. This would need a camera with a very large aperture. How can we know if claims made by the military about their secret technology is true? Is military science really so far ahead of the stuff we know about or do they just say it is?

__Interference__

- Deriving the equation for the intensity distribution of two slits is too advanced for this course so we just calculate the position of the maxima in the interference pattern and the first diffraction minima then fill in the rest.
- In the GeoGebra simulations embedded below the waves don't really reflect of the barriers, they are separate waves that are programmed behave in the same way. Can such simulations be used to make predictions or are they only useful for helping to visualise situations.tion and deduce so much.

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

__Doppler__

- Doppler effect applies to sound, water and light waves, same model for different phenomena.

__Diffraction__

- The idea of modelling the propagation of a wave by considering many wavelets is also used in quantum mechanics. Huygens in 1650 would have had no idea of such things.

__Interference__

- Rotating vectors can again be used to get a mathematical model for the intensity distribution for two slits and show why increasing the number of slits reduces the width of the maxima.
- Joseph Fraunhoffer's observation of colours as alcohol evaporated from a sheet of glass is an example of serendipity.

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

**worksheets and exercises**

__Multi choice__

__Problems__

__Labs__

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

Ripple tank simulation (GeoGebra).

Ripple tank simulation (GeoGebra)

Phase and reflection (GeoGebra)

Thin film video#### 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 *