Homework Assignment #6 Physics 397

(due 3/19/12)

Reading

(i) How Things Work (HTW) : 14.3 (Lasers and LEDs) (ii) Handout 8: “Amazing Light”, J.L. Bromberg, Invention and Technology, Spring 1992. (iii) Handout 9: “The Dawn of Miniature Green Lasers,” Scientific American, April 2009. (iv) Handout 10: “Bar Codes Sweep the World”, Invention and Technology, Spring 1993.

Questions/Problems

1. A CD player uses a beam of laser light to read the disc, focusing that light to a spot less than 10-6 m in diameter. Why can’t the player use a cheap incandescent lightbulb or an light-emitting diode (LED) for this task rather than a more expensive diode laser?

2. Why doesn’t increasing the current passing through an LED affect the color of its light?

3. Why does increasing the current passing through an LED affect the brightness of its light?

4. Please describe in a minimum of four sentences the development of the laser.

5. Please describe in a minimum of four sentences the challenges and the applications of miniature green lasters.

6. What were the two technological developments of the 60s that made bar codes affordable and how did they do so? Towards the Presentation/Paper

1. Please write down the key physics concepts involved in the device you’ll describe in your paper/presentation.

2. Please write an outline for your paper where you make sure to focus on what your device does and how it works. You may also want to include, if appropriate, some history of its invention/development for context and also some discussion of future applications/developments/directions.