Planks Constant kit can be used:
As a direct method that gives a reasonable order of magnitude value for Plancks constant, h
For the demonstration of photoelectric effect and the principle of applying a backing p.d. to reduce anode current to zero
The Plancks Constant Kit contains a photoelectronic unit, with six colour filters and a BNC to 4mm plug lead. The main unit contains a photoemissive Caesium Antimony cathode, with a spectral response of 185-650nm. When light of frequency, f, strikes the cathode, electrons of energy E=hf-W0 are released and would normally reach the anode, producing a current which can be registered on a very sensitive instrument such as a Picoammeter or an Electrometer.
The p.d. from an internal PP3 (6F22)-type cell can be adjusted to a value V where the anode current is just reduced to zero. V is proportional to the frequency of light used. This apparatus enables values of V to be found for various frequencies of light selected by placing each of the colour filters in turn over the cell. A plot of V vs. f gives a reasonable straight line where the gradient is h/e.
Items in the kit are available separately, and also a set of three narrow band filters for mercury violet, green and yellow lines from the spectrum of a mercury discharge lamp. These give a similar graph of the same gradient.
Contents include one of each of the following (which are available separately):
Plancks Constant Unit with screened lead
Colour Filters set of six for F4H28615
Set of 3 Narrow band filters
Plus the following metering:
Easy-Read Meter
20V d.c. Attachment
Spacesaver Picoammeter