This set of equipment uses the traditional vacuum photocell method to measure Planck's Constant. Although photocurrents as small as 10^-12A are measured during the experiment, the outstanding stability of the electronics and the excellent shielding allow the work to be carried out under normal laboratory conditions. Similarly, the use of high quality 11-layer interference filters allows the experiment to be performed in a normally lighted laboratory.

The procedure for measuring Planck's Constant is simple: After the lamp and amplifier are warmed up, the lamp and photocell units are placed facing each other about 50cm apart. The cap and cover are removed from the photocell unit and the image of the lamp is focused on the cell's cathode. The cover is replaced, and photocurrent vs. bias voltage curves are recorded with each of the interference filters fitted in turn. Planck's Constant may be calculated from the zero-crossing points of the curves. The procedure is fully described in the accompanying manual; results within 5% of the accepted value may be reliably obtained. The apparatus consists of four matched units:

• A 50 W high pressure mercury lamp
• A vacuum photocell with a nickel ring anode and an Ag-O-K mixed cathode, mounted in a shielded box
• A set of five interference filters with band pass widths of less than 50nm and transmissions centered at 365.0nm, 404.7 nm, 435.8nm, 546.1nm, and 577.0nm
• A Picoampére Amplifier and Control Unit that supplies the -2V - +2V bias voltage to the photocell and measures the photocurrent. The unit measures currents in the range ±2.0 x 10^-9A to ±0.1 x 10^-13A and indicates them on a built-in 3.5-digit LED display. Parallel outputs on the rear panel allow the photocurves to be recorded using a computer interface or XY-recorder. Shielded cables for connection to the photocell unit are included

• Amplifier/Control Unit is 31 x 28 x 17.5 cm
• Light Source is 12 x 20 x 28.5 cm
• Photocell Unit is 8 x 20 x 26.5 cm

• 115VAC
• Power cord measures 1.8m