Hinglish

Shadow Formation

Class 7 Science · Chapter 11: Light: Shadows and Reflections · NCERT Curiosity section 11.4

Learn

In a dark room, Zoya holds a cardboard star between a torch and the wall: a dark star-shaped patch appears. Light travels straight, so the opaque object blocks it, and the region where light cannot reach is the shadow. To see one you need a light source, an opaque object and a screen (a wall, floor or ground).

Opaque objects cast dark shadows, translucent ones lighter shadows, and even some transparent objects a faint one. Moving the object closer to the torch makes the shadow bigger; moving it closer to the screen makes it smaller and sharper. Tilting changes its shape. Painting the object a new colour does not change the shadow's colour.

Outdoors, your shadow is long in the morning and evening and shortest around noon, when the Sun is high. India has a rich tradition of shadow puppetry: Tholu Bommalata of Andhra Pradesh, Togalu Gombeyaata of Karnataka, Ravana Chhaya of Odisha and Tholpavakoothu of Kerala tell stories with cut-out figures between a lamp and a screen.

Explore: what happens to the shadow?

  1. Sort each action.

Remember

  • A shadow forms where an opaque object blocks light; you need a source, an object and a screen.
  • Shadow size and sharpness depend on positions; shadow colour does not depend on object colour.

Quick check

What happens to the shadow of a ball if the torch is switched off?

  1. there is no shadow
  2. it gets bigger
  3. it turns red
  4. it gets sharper
Answer

there is no shadow. A shadow needs a light source.

Think about it

How could you use shadows to tell the time without a clock?

One answer

Stand a stick upright in the sun and mark where its shadow falls at different hours; the shadow's direction and length change through the day, like a sundial.

Practice

Practise with fresh questions at three levels (easy, medium, hard), some answered hands-on, with hints and worked answers. Get 4 of your last 5 right to finish the topic.