2.13 Quarks and photons

This video contains these scenes: 1. Image of a carbon atom, with a bundle of red and green spheres in the centre, surrounded by blue spheres. Each red sphere represents a proton, containing 2 purple spheres and 1 yellow sphere (3 quarks). Each green sphere represents a neutron, containing 1 purple sphere and two yellow spheres (3 quarks). Each blue sphere represents and electron; 2. Image showing quark flavours – up and down, charm and strange, top and bottom. They are shown as spheres labelled with the first letter of the flavour, with u, c and t coloured purple, and d, s and b coloured orange; 3. Drawing of the electromagnetic spectrum, in order of increasing wavelength, decreasing frequency: a. Gamma rays (lowest wavelength) b. X-Rays c. Ultraviolet d. Visible (expanded into colours violet, blue, green, yellow, orange, red) e. Infrared f. Microwaves g. Radio waves The final sentence should read ‘Photons with a wavelength of around 400–700 nm are visible to humans, as shown here.’; 4. Line graph of photons absorbed / % (percent) against wavelength / nm, over the range 400 – 700 nm). The percentage absorbed is close to 100 percent for around 400 – 500 nm, falls to around 20 % between 500 and 570 nm (the range of wavelengths of light absorbed by chlorophyll), then rises to over 90% at around 660 nm, then falls to almost zero by 700 nm. The line is labelled ‘pigment extract’; 5. Drawing of a green leaf. Photons of different wavelengths are shown as coloured arrows pointing downwards towards the leaf. A green arrow shown pointing upwards from the top of the leaf, is labelled ‘some green light is not absorbed but reflected.’ A green arrow shown pointing downwards from under the leaf is labelled ‘green light can also be transmitted through the leaf’. The leaf is also labelled – ‘photons of many wavelengths are absorbed by leaves and power photosynthesis’.