Robert Cinca - Physics
Conclusion
My research question was: “How does the final current affect the surge current
time in a filament bulb?” My results indicate that there is an inverse-square
relationship between the final current and the surge current time, over the range I
have used (0.06A to 0.32A). This is in agreement with the hypothesis reasoned in
Part 1 of my essay (the Logical Argument). Through my experiment, I have also
uncovered two other interesting relationships:
the time taken to reach the maximum surge current was possibly as a result of
self-inductance of the filament creating a back electromotive force.
there was a linear relationship between the maximum surge current and the
final current.
My experimental results are also supported by my hot body radiator excel model.
The model has a surge current, similar final temperatures and shows an inverse
square relationship between the surge current time and final current. Some
differences arose: my experimental results took much longer to reach the final
steady current than my model suggested. This may have been caused by the
volume expansion of tungsten and due to a varying emissivity of tungsten with
temperature. Another difference was that in the model the surge current happened
instantaneously. In my experiment the maximum surge current was reached after
about 0.005 seconds. This is possible due to the back e.m.f. produced by self-
inductance of the filament.
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