Easy to use

With this compact apparatus it is extremely easy for students to do experiments themselves to determine Planck’s constant using the stopping potential method with high accuracy. This is achieved by means of some special technology in which only the frequency of the maximum light wavelength output by the LED contributes to the result. This makes the five LEDs supplied act as monochromatic sources of light with accurately defined wavelengths.

The LED sockets are equipped with special couplings which ensure they are screened from all external light. With the help of two potentiometers for coarse and fine adjustment of the photoelectric current in the nA (nanoamp) region plus two four-decade displays, the photoelectric current can easily be calibrated to zero and the corresponding stopping potential can then be read off. It is also possible to demonstrate by this means that the intensity of the light has no effect on the kinetic energy of the photo-electrons.

Various evaluation methods

First measurements can be plotted. The gradient of the resulting straight line can then be used to obtain the value of Planck’s constant. At the same time, the work function for the cathode material can also be determined. Both these two values can also be obtained purely by calculation with the help of a spreadsheet program.


19.10.00  Compact equipment for the determination of h

04.09.00  2 Experiment lead, 75 cm

19.20.10  LED unit, 472 nm

19.20.20  LED unit, 505 nm

19.20.30  LED unit, 525 nm

19.20.40  LED unit, 588 nm

19.20.50  LED unit, 611 nm

19.20.60  Protective cap for photocell

Additionally required:

00.05.10  Low voltage power supply MKS 2.4


00.05.20  Low voltage power supply MKS 3.1