a) State the energy changes that occurred
Torch vanes rotating vanes
[light energy] ---> [ heat energy ] ---> [ kinetic energy]

b) If a brighter light source is used, will the vanes rotate faster or slower?
1 point: They will rotate faster
1 point: A brighter light source means that there is more light energy provided. More light energy will be converted into more heat energy at the vanes, which translates into more kinetic energy. More kinetic energy means faster speed.

c) When the light source was removed, the vanes stopped rotating after a while. Explain why this is so.
The light source is the source of light energy. Without the light energy to convert to heat energy at the vanes, the vanes would no longer be gaining kinetic energy and therefore they will stop.

(a longer explanation is that more light energy is absorbed by the black parts of the vanes. Black absorbs light, and white objects tend to reflect light. This results in heat energy around the air near the black part of the vanes, and the heat warms the air molecules next to the black parts of the vanes. The air molecules get all heated up and move more quickly, gaining kinetic energy, and they 'push' the black part of the vanes , and cause them to rotate. IF the vanes were both black on the sides facing the light source, rather than one black and one white van, then they would both absorb the light and heat the air equally and the vanes wouldn't be able to move. you have to heat only one side so it would move.)