Learning physics by experiment: VIII. Radiation

"The ideal range of values for the UV index in a particular environment is 3.0 to 7.0. If a UV bulb produces a UV index of 1.8 at a distance of 42 cm, what distances are required to create the ideal range?" This is the essence of an electronic message from a non-scientific friend. A subsequent meeting revealed some major difficulties, including (a) the non-trivial location of the effective center of the bulb when placed in a reflective shade and (b) severe limitations in measuring values for other distances due to various constraints. Such problems caused the initial solution from an intentionally simplistic analysis to be reconsidered. An empirical approach with minimal laboratory equipment resolved item (b), but the challenge of item (a) resisted any experimental technique. Theoretical methods were then devised to identify the equivalent point source of the lamp, thereby producing a calibration curve for the lamp that applies to any environment. This success further extends the power of the philosophy implemented for more than ten years {nominal bookends in [1,2]}, with special emphasis on the benefits of showing students how physics solves problems in the real world.

 

[1] APR10.Z11.7*; [2] MAR21.H71.49* (* in meetings.aps.org)