How To Trap Laser In A Waterfall?

 Overview 

This experiment Laser Trapped in a Waterfall teaches us light science, Total Internal Reflection. you can see the light will go forward within the waterfall and it appears that light is bend.

Age: 5 +          Time: < 10 mins

 Safety 

1. Adult supervision.
2. Keep that laser away from everyone's eyes.

 Materials List 

• Plastic bottle
• Water
• Greenlight pointer
• Awl

 Instruction 

Step 1/3 – Use an Awl to poke a hole in the middle of the bottle.

Step 2/3 – Add water to the bottle so that the water will flow out of the hole you poked.

Step 3/3 – Point the light through the water at the hole where the water is running out of.  Observe the track of the light.

 Troubleshooting 

Why is my water not flowing out of the air, but flowing along the wall of the bottle?
- Add more water to increase the water pressure.

Why does my look that light is scattered?
- Make sure you point the light at the hole through the bottle?

 Question to Ask 

Why do we need a green light pointer? Can I use a flashlight?

 Scientific Description 

This is an explanation of total internal reflection, which occurs when a beam of light hits a medium boundary (the edge of the water in this experiment) at a certain angle, so it reflects, rather than goes straight through. This happens over and over again as the light hits each boundary in the waterfall. As you can see the light is going forward within the water. The light is bent, some may say, but it just bounces forward within the water in a straightway. A total internal reflection wants two requirements.

First of all, the light must be inside a more dense medium, and also approaching the boundary of a less dense medium - In this experiment, the water travels from water into the air, for example.

Secondly, the light must hit that medium boundary at an angle greater than something called the 'critical angle'.

 Extensions 

1. We can change the green light pointer to another color.
2. Point the light at the hole with the different light pointer at the same time.
3. Can we try a flashlight?