Error propagation for value not directly measurable

AI Thread Summary
The discussion centers on calculating the error in the boundary frequency (\nu) for the photoelectric effect, given by the formula \nu = \phi/h. The user initially applies the product/division rule for error propagation, suggesting that the errors in \phi and h can be combined to find the error in \nu. However, the instructor emphasizes the need to include systematic errors from the voltage measurement, which complicates the error propagation. The user seeks clarification on whether to ignore the error in \phi and instead rely solely on the voltage error provided by the multimeter. The conversation highlights the importance of considering all sources of error in measurements for accurate calculations.
sunrah
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Homework Statement


This should be very simple:
Given the following (boundary frequency for photoelectric effect):

\nu = \frac{\phi}{h}

what would be the error on \nu?

Homework Equations


The Attempt at a Solution



\varphi and h are both determined through linear regression (y = mx + c). Where

h =em and \varphi = -ec. The errors on m and c are supplied courtesy of computer software.

My understanding is that the product/division rule for error propagation can be used:

\delta \nu = \nu\sqrt{(\frac{\delta \varphi}{\varphi})^{2}+(\frac{\delta h}{h})^{2}}

my instructor disagrees
 
Last edited:
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Sounds right to me. What's your instructor's idea for how to propagate the error?
 
well, i spoke to her now and she says that the systematic error on the voltage (digital multimeter) should be included.

eU = h\nu + \varphi (1)

where \varphiis the work function.
The boundary frequency is given as \nu_{b} = \frac{\varphi}{h} (2)

Of course we can write the \nu_{b} in terms of voltage using (1), but we determined \varphi and h using linear regression which also supplied the standard error on those values. I'm not really sure how to determine the errors on \nu_{b} now. Should I ignore the error on \varphi, combine (1) and (2) and just use the error for the voltage provided by the multimeter manufacturer?

\delta \nu_{b} = \nu_{b} \sqrt{(\frac{\delta h}{h})^2 + (\frac{\delta U}{U})^2}
 
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