Pinhole Camera, Periscope and Kaleidoscope

Class 7 Science · Chapter 11: Light: Shadows and Reflections · NCERT Curiosity section 11.7–11.8

Learn

In a dim room, Zoya places a candle in front of a card with a tiny hole, with a screen behind. An image of the flame appears on the screen, but upside down! Light from the top of the flame travels straight through the hole and lands low; light from the bottom lands high. This is a pinhole camera.

They build one from two boxes that slide into each other: a pinhole in the bigger box, a tracing-paper screen in the smaller. Pointed at a sunny tree, it shows a coloured, inverted image. A plane mirror's image is laterally inverted but not upside down; a pinhole camera's image is upside down.

Two plane mirrors at the ends of a Z-shaped tube make a periscope, letting you see over a wall or a crowd; submarines and soldiers in bunkers use them. Three mirror strips joined in a triangle inside a tube, with broken bangle pieces at one end, make a kaleidoscope: reflections of reflections create a new pattern every time you turn it.

Explore: which device is it?

1. Sort each description.

Remember

• A pinhole camera forms an upside-down image because light travels in straight lines.
• A periscope uses two mirrors; a kaleidoscope uses three mirrors to make patterns.

Quick check

How does the image in a pinhole camera look?

1. upside down
2. erect and the same
3. always black
4. invisible

Think about it

What happens to a pinhole camera's image if you make the hole much bigger?

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.