Error propagation for value not directly measurable

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SUMMARY

The discussion focuses on error propagation for calculating the boundary frequency (\nu) in the context of the photoelectric effect, defined by the equation \(\nu = \frac{\varphi}{h}\). The values of \(\varphi\) (work function) and \(h\) (Planck's constant) are derived from linear regression, with their associated errors provided by software. The participant proposes using the product/division rule for error propagation, but their instructor emphasizes the need to include systematic errors from the digital multimeter when calculating the error on \(\nu\). The final error formula suggested is \(\delta \nu_{b} = \nu_{b} \sqrt{(\frac{\delta h}{h})^2 + (\frac{\delta U}{U})^2}\).

PREREQUISITES
  • Understanding of linear regression and its application in determining constants.
  • Familiarity with error propagation rules, specifically the product/division rule.
  • Knowledge of the photoelectric effect and related equations.
  • Experience with digital multimeters and their systematic error characteristics.
NEXT STEPS
  • Study error propagation techniques in experimental physics.
  • Learn about systematic versus random errors in measurement.
  • Explore linear regression analysis using software tools like Python's SciPy or R.
  • Investigate the implications of measurement uncertainty in scientific experiments.
USEFUL FOR

Students and researchers in physics, particularly those working on experiments involving the photoelectric effect, error analysis, and data interpretation from linear regression.

sunrah
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Homework Statement


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

[itex]\nu = \frac{\phi}{h}[/itex]

what would be the error on [itex]\nu[/itex]?

Homework Equations


The Attempt at a Solution



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

h =em and [itex]\varphi = -ec[/itex]. 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:

[itex]\delta \nu = \nu\sqrt{(\frac{\delta \varphi}{\varphi})^{2}+(\frac{\delta h}{h})^{2}}[/itex]

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.

[itex]eU = h\nu + \varphi[/itex] (1)

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

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

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

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