A photoelectric-effect experiment determines Planck's constant from the stopping…

PHYSICS · Multi-part · Fermi University Physics · Scientific Practice & Experimental Methods · Records, communication and the epistemology of evidence · Records, communication and the epistemology of evidence

Measurement and Method, Ch Writing the result, and the integrity of the data behind it

Problem

A photoelectric-effect experiment determines Planck's constant

h

from the stopping voltage

V_{\mathrm s}

measured for six LEDs of different colours (frequency

\nu

), using

eV_{\mathrm s} = h\nu - \phi

, where

e

is the elementary charge and

\phi

is the work function of the photocathode. Student A took all six sets of readings. Student B wrote the least-squares fitting script, carried out the fit, and has read the final report and is willing to take responsibility for all of it. Fitting all six points gives

h = (5.9 \pm 0.5)\times10^{-34}\,\mathrm{J\,s}

with

\chi^2_\nu = 4.2

. The logbook records, timed during the run: "14:07, blue-violet LED: forward current drifting upward as the LED warms;

V_{\mathrm s}

reading falling steadily over 3 minutes, not settling." Excluding that one point, the fit gives

h = (6.55 \pm 0.18)\times10^{-34}\,\mathrm{J\,s}

with

\chi^2_\nu = 1.1

. The submitted report states only: "One point was excluded to improve the fit;

h = (6.55 \pm 0.18)\times10^{-34}\,\mathrm{J\,s}

." Student A is listed as sole author; student B is thanked in the acknowledgements "for help with the coding." ((a)) Judge whether the printed sentence meets the disclosure standard, and rewrite it so that it does, using the numbers above. ((b)) Apply the two conditions for authorship to decide whether student B should be listed as an author rather than acknowledged, and give the acknowledgement text if not. ((c)) Eight months later, a marker asks why the blue-violet LED point is missing from the graph. Name the three records that would answer this question and state what each must contain.

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