A bothersome feature of many physical measurements is the presence of a backgrou

Question

A bothersome feature of many physical measurements is the presence of a background signal (commonly called "noise"). In an experiment, some light that reflects off the apparatus or from neighboring stations strikes the photometer even when the direct beam is blocked. In addition, due to electronic drifts, the photometer does not generally read 0.0 mV even in a dark room. It is necessary, therefore, to subtract off this background level from the data to obtain a valid measurement. Suppose the measured background level is 4.6 mV. A signal of 20.2 mV is measured at a distance of 30 mm and 15.6 mV is measured at 34 mm. Correct the data for background and normalize the data to the maximum value. What is the normalized corrected value at 34 mm?

Explanation / Answer

The background-corrected light measurement at 30.0 mm is 20.2 mV- 4.6 mV = 15.6 mV The corrected light measurement at 34 mm is 15.6 mV - 4.6 mV = 11.0 mV So Normalize the data to the maximum value probably means to set the peak value to unity and scale the remaining data by the same factor. Which means divide everything through by 15.6 mV. Therefore, the normalized corrected value at 34 mm is (11.0 mV)/(15.6 mV) = 0.705

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