How Shadows Are Formed

• State the conditions needed to form a shadow.
• Explain why shadow size changes with source distance and time of day.
• Identify umbra-like dark part in simple classroom activities.
• Use shadow observations in Indian settings like noon sun and monsoon clouds.

Level 1 - Conditions for shadow

A shadow forms when three things are present: a light source, an opaque object, and a screen/surface. No light means no shadow. Transparent objects make almost no visible shadow.

Level 2 - Position matters

When object moves closer to light source, shadow becomes bigger. When object moves away from source, shadow becomes smaller. This is easy to test using a torch and a hand.

Level 3 - Daytime changes

In morning and evening, Sun is lower, so shadows are longer. At noon in India, the Sun is high, so shadows are shortest. This helps in estimating approximate time outdoors.

Level 4 - Local context

Children playing cricket in a school ground in Delhi notice long shadows during evening practice. During monsoon, thick clouds reduce brightness, so shadows become faint. Farmers use tree shadows for resting spots in summer.

NCERT anchor: Looking Around 4, Ch 7 — From the Window; Ch 19 — Abdul in the Garden (sunlight direction and shade)

Hand shadow with torch

Step 1 - Place white chart paper as screen.
Step 2 - Hold your hand between torch and screen.
Step 3 - Move hand closer to torch; observe larger shadow.
Step 4 - Move hand closer to screen; observe sharper smaller shadow.
Answer: Shadow size depends on relative distances.

School flagpole shadow

Step 1 - Measure shadow at 9 AM, 12 PM, and 4 PM.
Step 2 - Record lengths in a table.
Step 3 - Compare values; noon is shortest.
Step 4 - Explain using Sun's position in sky.
Answer: Higher Sun gives shorter shadow.

• List the three requirements for shadow formation.
• Why is your shadow longer at 5 PM than at noon?
• Will a clear plastic sheet form a dark shadow?
• What happens to shadow if source is brought nearer?
• Stretch: Create a daily shadow clock with a stick and mark direction and length every hour.

Revision tip: Shadow rule: light source + opaque object + screen; change any one, shadow changes.

Open the Practice tab for graded questions on How Shadows Are Formed.