Three things for a shadow

The idea

A shadow forms when an object blocks light from falling on a screen, so observing a shadow needs a source of light, an opaque object and a screen (any wall, floor or ground).

A shadow in the dark?

Stand in a dark room with no light. Hold your hand up in front of a wall.

What do you need to see a shadow?

• A light, an object and something for it to fall on
• Just an object
• Only a screen

Take each thing away

Take away the light, the object and the screen, one at a time. Then put them back.

Light, object, screen

With one of the three missing, there was no shadow to see. A wall, a floor or the ground can be the screen.

A shadow forms when an object blocks light from falling on a screen, so observing a shadow needs a source of light, an opaque object and a screen (any wall, floor or ground).

• You need | For example
• A source of light | The Sun or a lamp
• An opaque object | Your hand
• A screen | A wall, the floor or the ground

Notes

A shadow forms when an object blocks light from falling on a screen, so observing a shadow needs a source of light, an opaque object and a screen (any wall, floor or ground).

Check yourself

Which three things are needed to see a shadow?

In daily life, what can act as a screen for a shadow?

In a dark room, with no source of light, what happens?

You stand in the Sun. What is the source of light, and what is the screen?

• A source of light, an opaque object and a screen — correct. Yes! All three are needed.
• A mirror, an opaque object and a lamp. A mirror is not needed. A screen is.
• A lamp and a screen only. An opaque object is needed too.
• The opaque object. The object blocks the light. The shadow falls on the screen.
• The wall, the floor or the ground — correct. Yes! Any of these.
• The lamp. The lamp is the source of light, not the screen.
• A shadow forms anyway. Without a source of light there is nothing to block.
• The shadow is darker. There is no light, so there is no shadow to see.
• No shadow can be seen — correct. Yes! A shadow needs a source of light.
• The Sun is the source and the ground is the screen — correct. Yes! Your shadow falls on the ground.
• You are the source and the Sun is the screen. You block the light. You are the opaque object.
• The ground is the source and the Sun is the screen. It is the other way round.