One could then get a stick 1 centimeter long with no markings and repeat
this process getting about 463 centimeters plus say 7 tenths of a
centimeter (millimeter) plus or minus 1 millimeter. Now we have 4 sig
figs. This process also shows nicely why a smaller unit gives a
measurement with less error.
It seems to me that students need to realize that the accuracy of a
measured result is not necessarily determined by the precision limit of
the measuring device. In lab I have students measure the focal length of
a 5-diopter lens by imaging a distant source on a screen. In this
experiment the depth of field is varied using suitable apertures. With a
long depth of field the focal length cannot be measured to the nearest
millimeter even by using a ruler with a millimeter scale.
Gene
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Eugene (Gene) P. Mosca Phone 410-293-6659 (Fax 3729)
Physics Department 410-267-0144 Home
572 Holloway Road 610-683-3597 Summer
U.S.Naval Academy Mailstop 9C, Michelson Rm 339
Annapolis MD 21402 email: mosca@nadn.navy.mil
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