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๐ฌ Think about it
Can you see a candle flame through a bent pipe? Try it and you will fail. That simple trick hides a big truth about how light moves. Let us test it with matchboxes and a pipe.
How do we know light travels in a straight line?
- Light passes through holes only when they are in a line.
- If one hole is moved, the light spot disappears.
- A candle flame is seen through a straight pipe.
- It cannot be seen through a bent pipe.
Example:
You can see a friend through a straight cardboard tube, but not if you bend the tube.
In this Activity, we will line up holes in matchboxes to see if light travels straight.
Materials needed
Three matchboxes, a torch, and a cardboard screen.
Procedure
1. Make a hole in the inner tray of each matchbox at the same position.
2. Arrange the three matchboxes in a straight line with the holes at the same height.
3. Place a torch on one side with its lamp at the height of the holes.
4. Place a screen on the other side and get a bright spot on it.
5. Move one matchbox slightly to a side or up and down.
6. Check if the light spot still appears on the screen.
2. Arrange the three matchboxes in a straight line with the holes at the same height.
3. Place a torch on one side with its lamp at the height of the holes.
4. Place a screen on the other side and get a bright spot on it.
5. Move one matchbox slightly to a side or up and down.
6. Check if the light spot still appears on the screen.
Observation
A bright spot appears only when all three holes are in a line. Moving one box makes the spot disappear.
Explanation
Light reaches the screen only when the holes are in a straight line. So light travels in a straight line.
โ Summary
- Holes lined up straight
- Bright spot appeared
- One box moved, spot gone
- Light travels straight
In this Activity, we will look at a candle flame through a straight and a bent pipe.
Materials needed
A long hollow pipe of flexible material and a candle (used under adult supervision).
Procedure
1. Align the straight pipe so you can see the candle flame.
2. Now bend the pipe and try to see the candle flame again.
3. Check whether you can still see it.
2. Now bend the pipe and try to see the candle flame again.
3. Check whether you can still see it.
Observation
The flame is seen through the straight pipe but not through the bent pipe.
Explanation
Light cannot turn around the bend, so the flame is hidden. This shows that light travels in a straight line.
โ Summary
- Straight pipe, flame seen
- Bent pipe, flame hidden
- Light cannot turn
- Light travels straight
Important Points
- Light travels in a straight line.
- It is blocked if the straight path is broken.
โ Test Yourself
-
In what kind of line does light travel?
View Answer
A straight line. -
When does the light spot appear in Activity 11.1?
View Answer
Only when all three holes are in a straight line. -
Can you see a flame through a bent pipe?
View Answer
No, only through a straight pipe. -
Why does the flame vanish in a bent pipe?
View Answer
Light cannot turn around the bend. -
What should you do near a lit candle?
View Answer
Use it only under adult supervision.
