# Physics 2.3 AS91170 Demonstrate understanding of waves.

Link to NZQA information relevant to this standard.

The subject content for Physics 2.3 divides into two fairly separate sections: Waves and Light.

• reflection and refraction at a  boundary (including phase and wave parameter changes)
• superposition of pulses
• diffraction through a slit
• 2-point source interference (qualitative).
• reflection in curved mirrors
• refraction through lenses
• refraction
• total internal reflection
• critical angle at a plane boundary.

Teaching diffraction and interference: notes from Howard Lukefahr:

```Diffraction and interference are really just different manifestations of the same underlying physics. The principle of superposition  tells us that the displacement of a medium due to two waves is just the sum of the individual waves. In other words, waves add and cancel. This is the underlying physics. One can show simple diagrams of this that are seen in many textbooks, something like this.

But is this really true? Can waves cancel? Can two louds make a quiet, can two brights make a dark, so to speak? Before launching into the geometry, show students it really works. Besides the usual double-slit interference where the dark bands show light waves cancelling (two brights make a dark), here are some useful resources for that: Sound Interference,  Diffraction and Interference of Water Waves,  Ripple Tank.
Use the Diffraction Grating Glasses. These very inexpensive and easy to use diffraction gratings are great for both qualitative and quantitative experiments and activities.

Note for teachers: Light or sound waves carry energy. If two light or sound waves cancel, where does the energy go? Answer.```