Using five LEDs of different colours

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 Models, idealisation and what a measurement is evidence for

Problem

Using five LEDs of different colours, a group measured the threshold voltage

V

at which each just begins to emit light, plotted

V

against the light's frequency

f

, fitted a straight line, and from its slope obtained

h_{\rm meas} = (6.55 \pm 0.15)\times10^{-34}\,\mathrm{J\,s}

, consistent within one combined standard uncertainty of the SI-defined value

h = 6.62607015\times10^{-34}\,\mathrm{J\,s}

exactly. Their report concludes: 'This proves that light is quantised and that the photoelectric equation is correct.' ((a)) Find the error in this conclusion. ((b)) State what the measurement is evidence for.

Browse the problem library