See below for many resources on this topic. Let me know if they are helpful, and if you have others to add to the list.
Waves and sound
Sounds Amazing, a resource for GCSE Physics (exams taken in the UK, usually at around 16 years old).
Simple wave simulator from physicsclassroom.com
Video of homemade wave machine http://thekidshouldseethis.com/post/how-to-build-your-own-wave-machine-physics-demo
Visualising sound waves (very cool) http://thekidshouldseethis.com/post/82296107912
Octobass on The Kid Should See This
Multilayered mechanized music making – using old vinyl records on a turntable and many other electronic and mechanical items.Again from The Kid Should See This.
Video of an opera singer and beat boxer under MRI scanner http://www.youtube.com/watch?amp;v=HhRn7E1LaLs
Vocal cords up close while singing http://www.youtube.com/watch?v=-XGds2GAvGQ
The Electromagnetic Spectrum
GCSE Bitesize activity with Geordie voiceover. Probably best for children who prefer auditory or visual learning styles.
Light and UV light
Corals fluorescing under different lighting conditions
Why is the sky blue? (We didn’t cover this in our first two classes but touched on it in the third class.)
Reflection and refraction: A Rube Goldberg machine on The Kid Should See This.