Experiment 2 — Shadow Play

Topic: Physics · Classes 4–5 · Light travels in straight lines; opaque, translucent, transparent

Aim: Make the shadow exactly twice as tall as the toy (a 20 cm shadow from a 10 cm toy).

Daily: Your shadow is long in the early morning and short at noon, because the Sun’s direction changes. A sundial uses exactly this to tell the time, and shadow puppetry — from Andhra Pradesh’s tholu bommalata to Kerala’s tholpavakoothu — is built on it.

Obs: No shadow appeared. The light passed straight through.

Should: Use the opaque toy. Transparent materials let light through and cast no proper shadow.

Why it happens: Transparent materials (clear glass, air, clean water) let light pass, so they cast no shadow. Translucent materials (butter paper, frosted glass) let some light through and cast a faint, fuzzy shadow. Opaque materials (wood, metal, you) block light completely and cast a sharp dark shadow. Shadows exist because light travels in straight lines and cannot bend around an object.

Question: You move the lamp closer to the toy. The shadow will…

Exp: A nearby lamp spreads its rays more steeply past the object, so the blocked region is larger.

Question: A shadow forms because light…

Exp: Straight-line travel plus an opaque blocker equals a shadow.

Question: Butter paper casts a faint shadow because it is…

Exp: Translucent materials let some light through.

Question: Why is your shadow in sunlight about your own size?

Exp: Nearly parallel rays give a shadow close to the object’s size.

Question: Toy 10 cm, lamp 20 cm from toy, screen 30 cm behind. Shadow?