Answer:
0°
Explanation:
The angle between force and displacement should be 0° in order to get the maximum work done.
Work done = Force x dcosФ°
Ф is the angle between force and displacement
When Ф is zero, the maximum work done is attained
When Ф is 90, the minimum work is done, in fact, work done is 0
Well, if your question is how light affects plants,
then you would want to design an experiment that plays aruond with the amount of light a plant gets
thus the thing changing (or variable) would be amount of light
