My PBL Project

INTRODUCTION

How does the laser light bend in the water spring?

The laser usually is not visible in air, although when it follows the water you can see the laser inside the water. The bending is because of the critical angle. When it hits the surface it refracts back to the water stream.

MATERIALS

Mandatory Equipment

¨ Laser pointer (red or green)

¨ Plastic soda bottle

¨ Water

¨ Sharp Instrument (for making a hole in the plastic

¨ bottle

PROCEDURE

First set up the soda bottle by drilling a hole near the bottom of the bottle. Begin with a drill bit that has a diameter which is slightly larger than the diameter of the laser that will be used.

First use something to cover up the hole and then fill the bottle with water. The cap will prevent leaking because it creates a vacuum in the bottle.

Have the bottle stand on top of objects so that the water can fall from the hole into the sink or other objects you use. Then, have the laser point through the bottle, the laser has to be stable and point exactly through the hole.

Carefully remove whatever you used to cover up the hole and then unscrew the top of the soda bottle. The light should reflect within the stream of water so that you could see at least a few points of reflection. The light should be visible through the entire stream.

If the reflections of the light isn't clear, it may be necessary to expand the hole by drilling through the existing hole with a larger drill bit. This process may need to be repeated several times.

SCIENTIFIC PRINCIPLE

My project uses Snell's law to find the critical angle. The Snell's law is a formula and it takes math skills to solve the equation. Below is an example.

When light crosses into a new medium, some of the light will refract (bend) and some of it will reflect. The angle of refraction is given by Snell's Law.

Where n is the index of refraction, a property unique to each material. This, and the reflection, is shown in the following diagram.

gpLight refracts and reflects at the barrier between air and water.

Where θ1 is the angle of incidence, or the angle of the source of light, θr is the angle of reflection, and θ2 is the angle of refraction.However, Snell's Law will result in error when n1 is greater than n2. This is called a critical angle, and it is the minimum angle at which all light is reflected. The critical angle can be defined by:

Safety Regulations

¨ Use caution when working with sharp objects.

¨ Do not shine a laser pointer, or any other light source, into your eyes or another person's eyes.

¨ Wipe up any spills immediately. People may slip in spills of water on the floor.