Speed of Light
In this lab we will study the speed of light.
Background
As a little bit of background research, you might consider saying a little bit about why it was important to measure the speed of light, who it was who first did so, and how.
Laser Safety
The U.S. Dept. of Health, Education and Welfare regulates laser manufacturers to see that users are not endangered. The federal government classifies lasers according to their power levels and specifies appropriate safety features for each level.
- CLASS I LASERS: Class I lasers are low-powered and do not emit hazardous radiation under normal operating conditions because they are completely enclosed. Class I lasers are exempt from any control measures. Equipment, such as laser printers and laser disc players, are examples of this class.
- CLASS II LASERS: Class II lasers emit accessible visible laser light with power levels less than 1 mW radiant power and are capable of creating eye damage through chronic exposure. The human eye blink reflex, which occurs within 0.25 seconds of exposure to the Class II laser beam, provides adequate protection. It is possible to overcome the blink response and stare into the Class II laser long enough to damage the eye. Class II lasers are exempt from any control measures. Equipment, such as some visible continuous wave Helium-Neon lasers and some laser pointers, are examples of Class II lasers.
- CLASS IIa LASERS: Class IIa lasers are special purpose lasers that emit accessible visible laser light with power levels less than 1 mW radiant power and are not intended for viewing. This class of lasers causes injury when viewed directly for more than 1,000 seconds. Class IIa lasers are exempt from any control measures. Equipment, such as some bar code readers, are examples of Class IIa lasers.
- CLASS IIIa LASERS: Class IIIa lasers are systems with power levels of 1 to 5 mW that normally would not produce a hazard if viewed for only momentary periods with the unaided eye. They pose severe eye hazards when viewed through optical instruments (e.g., microscopes, binoculars, or other collecting optics). Class IIIa lasers must be labeled. A warning label shall be placed on or near the laser in a conspicuous location and caution users to avoid staring into the beam or directing the beam toward the eye of individuals. Equipment, such as some visible continuous wave Helium-Neon lasers and some solid state laser pointers, are examples of Class IIIa lasers.
- CLASS IIIb LASERS: Class IIIb lasers are systems with power levels of 5 mW to 500 mW for continuous wave lasers or less than 10 J/cm² for a 0.25 s pulsed laser. These lasers will produce an eye hazard if viewed directly. This includes intrabeam viewing or specular reflections. Higher power lasers in this class will also produce hazardous diffuse reflections. Specific control measures covered in Class IIIb lasers shall be used in areas where entry by unauthorized personnel can be controlled. Entry into the area by personnel untrained in laser safety may be permitted by the laser operator if instructed in applicable safety requirements prior to entry and provided with required protective eye wear.
- CLASS IV LASERS: Class IV lasers are systems with power levels greater than 500 mW for continuous wave lasers or greater than 10 J/cm² for a 0.25 s pulsed laser. These lasers will produce eye, skin and fire hazards. This includes intrabeam viewing, specular reflections or diffuse reflections.
Take the following steps to ensure that optimum safety is achieved when the laser is being used.
- Do not look into the beam or stare at its bright reflections.
- Block off the beam at a point beyond the farthest point of interest. Use a dull, non-reflective object, such as a piece of wood.
- If the beam is to travel a long distance, keep it close to the ground or overhead so that it does not cross a walkway at eye level.
Experiments
In this lab, I would like you to really be an experimentalist. I am going to give you a basic idea of what you need to do, but then leave you to work out details. You will need to experiment, ask questions, and then refine - you should expect to redo experiments and try to determine what problems are if you run into any or if results do not work out.
Exercise 1: How can you determine whether a light source is a laser? What specific properties would you measure and how would you measure them to determine if a light source is a laser.
You should measure the speed of light in two ways:
- Speed of Light using a modulated laser
- Speed of Light using a microwave oven:
- Microwave ovens produce standing waves. Standing waves have maxima and minima. How might you use a microwave oven to measure the speed of light? How accurately and precisely can you measure the speed of light using a microwave oven?