(physics) concave mirror

to use / to employ / to make use of, to apply / to spend

observation

observe

reflection, reverberation / reflex (automatic response)

reflect, light, sound, radio waves, etc.

a light, beam, illumination / a gleam, glow, ray / a glimmer, shine, sparkle / a luster/lustre, polish, sheen / glory, influence, power / a glimmer, gleam / positive aspect

physics, the physical aspects of a phenomenon or a system

experiment

to do an experiment