The propagation of light

The propagation of light refers to how light travels through space or any medium. Light always moves in a straight line unless it is reflected or refracted by an object.

Observation in Daily Life:

• You might notice rays of light entering a dark room through a small slit in a door or a hole in the roof, especially in the afternoon when sunlight is strong.
• As the rays of light move towards the floor, they pass through the air, and you can sometimes see dust particles floating in the air.
• Normally, light is invisible as it travels, but when dust particles or small objects are in the way, they reflect the light.
• These dust particles make the path of light visible to our eyes, and we can clearly see that light moves in a straight line.
• This behaviour of light moving in a straight line is called rectilinear propagation of light.

Light entering through a window

1. Aim: The experiment aims to demonstrate how light travels in straight lines.

2. Requirements: three cardboards, a thick needle (to make holes), a candle, and matches or a lighter.

3. Procedure

• Take three pieces of cardboard and make a small hole using a thick needle in the centre of each.
• Arrange the cardboard so that the holes align perfectly in a straight line.
• Place a candle on one side of the aligned cardboard and light it.
• Look through the holes from the opposite side to see the candle's flame.

4. Observation

In Step 1, when the holes in the cardboard are perfectly aligned, you can see the flame because light travels in straight lines and passes through the aligned holes directly to your eye.

In Step 2, moving any of the cardboard out of alignment blocks the path of light, making the flame invisible. 

5. Conclusion: This experiment demonstrates that light travels in straight lines, as the flame is only visible when the holes are aligned and becomes invisible when the alignment is disrupted, confirming the linear propagation of light.

1. Aim: This experiment aims to investigate how the bending of a tube affects the path of light and the visibility of an object observed through the tube.

2. Requirements: a bendable tube, a candle, and a stand to hold the candle.

3. Procedure

Step 1: Position the candle on a stand and observe it through the straight tube to confirm initial visibility.

Step 2: Gradually bend the tube and attempt to view the candle through the tube once more.

4. Conclusion: The candle is visible when the tube is straight because the light travels in a straight line through the tube to the eye. When the tube is bent, the candle becomes invisible because the bend in the tube obstructs the straight path of light, demonstrating that light does not travel through curves within the tube.

This shows that light's propagation is linear and cannot navigate around bends or curves within a medium like a tube.

Looking at the candle