Measurement of Planck's constant Based on Planck's Radiation Theory

Abstract

Planck's constant measurement was based on the assumption that electrical power dissipated by the filament which emitted light entirely as radiation and the tungsten filament of the light bulb is a perfect black body. A phototransistor with a fixed frequency v measured the light intensity emitted over a narrow range of frequencies as an optical filter was employed in a dark room. The intensity of illumination which is analogous to intensity of radiation was deduced from Planck's radiation law and a relationship between the intensity of illumination (or radiation) was therefore established. A power law and an empirical R – T relation were used to calculate the temperatures corresponding to different resistances of the filament as the voltage was varied. The photocurrent was assumed to be proportional to the intensity of radiation and a linear regression fit to the data was used to determine the Planck's constant h, from the slope and the Planck's constant so obtained was 5.1227 x 10⁻³⁴Js with a percentage accuracy of 13%under laboratory conditions.