Reflection on a Plane Mirror, Virtual Image, Umbra and Penumbra

Integrated ScienceLight & SoundAges 12–13

Reflection mode: drag light source S to change the angle of incidence; the reflected ray, the normal, and both angles i and i′ are drawn and measured instantly (law of reflection: i′ = i). Extending the two reflected rays back, they meet at the virtual image S′, symmetric to S about the mirror, with S and S′ equidistant from the mirror. Shadow mode: drag the obstacle or the light source; a point source produces only an umbra, while a wide source also produces a penumbra region on the screen.