Another question from a reader. This is a Crookes radiometer. It is not in syllabus but the student is expected to be able to infer from the description and diagram. ( https://en.wikipedia.org/wiki/Crookes_radiometer )
The answers are:
(a) chemical energy (from inside the batteries) -> electrical energy (the electricity) -> light energy (from the bulb) -> heat energy (heating up the blackened vanes) -> kinetic energy (the vanes start moving)
(b) the vanes will rotate faster if a brighter light source is used. The black side of the vanes will absorb more light and get warmer, causing the vanes to move faster.
(c) The vanes would have lost its heat to the air in the glass, and to its surroundings. The kinetic energy of the moving vanes would also be gradually lost as it would be converted to heat and sound due to air resistance.
The inferences that students need to make are:
– light shining on black surfaces will be absorbed and converted into heat energy, while white surfaces will not absorb so much light energy.
– since the light is causing the vanes to turn, more light will imply the vanes will turn faster.
– the vanes stop when the light is turned off because there is no more energy being introduced to the vanes,
– and the vanes slowly lose its heat energy to the surroundings
– and its kinetic energy will be converted into heat and sound due to air resistance.