Learning objective: Test different materials and classify them as letting light through, blocking light, or letting some light through, based on the shadows or brightness observed.
Not all materials treat light the same way. A transparent material lets light pass all the way through it. Clear glass, like a window, is transparent — you can see right through it, and light passes through easily.
An opaque material blocks light completely — no light gets through it at all. Wood, metal, and thick cardboard are opaque. When light hits an opaque object, it can't pass through, so a dark shadow forms behind it, as shown in the diagram.
Some materials are in between — they let SOME light through, but not all of it, like a thin curtain or frosted glass. Light passing through these materials looks dimmer and blurry, rather than fully bright or fully dark.
You can test any material by holding it up between a light source and a wall. If you see a bright light spot on the wall, the material is transparent. If you see a dark shadow, the material is opaque.
Knowing which materials block light and which let it through helps explain everyday things — like why curtains make a room darker, why windows let sunlight in, and why standing behind a wall blocks you from being seen by light.
Light shines all the way through transparent materials, like clear glass. Opaque materials, like wood, block the light completely and make a dark shadow.
What does transparent mean?
What does opaque mean?
If light cannot pass through an object and a dark shadow forms, is the object transparent or opaque?
Find 3 materials at home (like paper, a window, and a book). Test each one with a flashlight or sunlight and decide if it is transparent or opaque.