Fiona did an experiment to find the relationship between the angle at which a ray of light strikes a mirror and the angle at which the mirror reflects the light. she placed a ray box in front of a mirror. she changed the angle at which the light from the ray box struck the mirror and noted the corresponding angle at which the mirror reflected the light.

which of the following is the independent variable in this experiment?

the mirror used to reflect the light
the ray box used as the source of light
angle at which the light from the ray box strikes the mirror
angle at which the mirror reflects the light from the ray box