Track quiz
Before the questions, here are the ten rules this track worked with.
| Idea | The rule, as the lab applies it |
|---|---|
| Light travels in straight lines | In air, light goes in a straight line. A wall in the way stops it. Light does not curve to follow a bent pipe. |
| A shadow is a place light did not reach | A dark shadow needs light, something opaque, and a surface behind it. Take any one away and it goes. A shadow shows only the outline of the object, not its colour. |
| How big, and what shape | Move the object nearer the lamp and its shadow grows. Move the screen back and the shadow grows too. Turn the object and only the outline changes. |
| A hole makes a picture | Light from the top of the object lands low on the screen. Light from the bottom lands high. So the picture flips upside down. A wider hole blurs the whole picture. |
| Light bounces off a smooth surface | Light hits a smooth surface and bounces off. The slant out equals the slant in, measured from the surface. Tilt the surface, and the light goes somewhere new. |
| What you see in a mirror | Your image stands as far behind as you stand in front. It is the same size. In an upright mirror it is the same way up. Left and right swap over. |
| Why a wall shows you nothing | A smooth surface reflects light all one way. A rough surface tilts each patch differently. So light scatters, and no picture survives. |
| Own light | A luminous object makes its own light. A non-luminous object does not. We see it when light from another source bounces off it. |
| Light through materials | An opaque material blocks all the light. A transparent material lets nearly all of it pass. A translucent material lets part of it pass. |
| The periscope | A simple periscope has two plane mirrors. They are parallel, each tilted at 45°. Light turns twice and reaches your eye. |
Three cards stand in a row. No light gets through. Why?
A red mug stands in front of a lamp. What colour is its shadow?
A puppet is walked towards the lamp. What happens to its shadow?
A comb is turned edge-on to the lamp. Why does its shadow lose its teeth?
In a pinhole box, why does the picture land upside down?
The hole is widened. What happens to the picture?
A torch shines at a mirror, almost flat. Where does the light go?
You stand 40 cm from a mirror. You step back to 90 cm. Where is your image?
Why can you see a wall, but not your face in it?
A stone lands in a still pond. Why does the reflection break up?
Why can you see the Moon at night?
A torch beam meets a thin cotton sheet. The screen behind is dim. What is the sheet?
A periscope's top mirror turns light down the tube. What does the bottom mirror do?
Now open Chapter 11, Light: Shadows and Reflections, in your NCERT book. Try its questions.
Next comes Earth, Moon, and the Sun. You now know what happens. Something opaque stands in the way of light.