Opaque, translucent and transparent materials
Physics · Key Stage 2 · The School
Three ways light meets a material
Shine a torch at different materials and light behaves differently each time. An OPAQUE material blocks light completely — wood, metal, thick card. A TRANSPARENT material lets nearly all light straight through — clear glass, clean water, clear plastic. A TRANSLUCENT material lets SOME light through, scattered — tracing paper, frosted glass, a thin curtain.
What each one does to a shadow
An opaque object blocks all the light, so it makes a strong, dark shadow. A transparent object barely makes a shadow at all, because almost all the light passes straight through it. A translucent object makes a faint, blurry shadow, because some light gets through while some is scattered.
Why frosted glass is not clear
Frosted glass is still glass, but its surface is rough at a tiny scale. Light hitting it scatters in every direction instead of passing straight through. You can tell there is light and shapes beyond it, but never a sharp, clear picture — that scattering is exactly what makes it translucent rather than transparent.
Four materials are tested with a torch in a dark room: a wooden ruler, a clear plastic ruler, greaseproof paper, and a mirror. The wooden ruler blocks the light completely — opaque, strong dark shadow. The clear plastic ruler lets almost all the light through — transparent, barely any shadow. The greaseproof paper glows softly but blurs the light — translucent, a faint shadow. The mirror blocks the beam and bounces it elsewhere entirely, which is a different behaviour again — reflection, not transmission.