In this experiment, students construct an equilateral triangle using graph paper, pencil, protractor and a ruler. They also make a "laser triangle" using a laser pointer and front-silvered mirrors.Students can use the geometric properties of an equilateral triangle combined with their understanding of the Law of Reflection to decide how to place the mirrors at each vertex so that the "laser triangle" fits their equilateral triangle.

**Warning:** Students should exercise extreme caution when using the laser pointers, since direct laser light entering the eye could cause retina damage.

### What Students Do

Students produce an equilateral triangle, ray-tracing of a retro-reflector, and build a retro-reflector using front-silvered mirrors.

### Materials You Will Need

**For each student group:**

- Laser pointer
- 1/2 inch binder clip
- 8.5 x 11 inch graph paper
- protractor
- ruler
- 3 front silvered mirrors

**Optional:** 3 CD jewel boxes to hold the mirrors in a vertical position

**Comments:** Send feedback on this lesson plan to **lessonplans@stardate.org** [4].

***TEKS** are Texas Essential Knowledge and Skills. For more information, visit http://www.tea.state.tx.us/teks/ [5].