Plank’s Constant Apparatus

Exp-1 To determine planck’s constant.
Exp-2 To verify the inverse square law.

This compact instrument consists of photocell, light source, a light receiving darkroom, digital display screen, display mode switch, current multiplier, light insensitive switch, voltage adjuster, voltage direction switch, indicator light and switch on/off. Six pieces of different color filters and four types of LED diodes are provided. The distance between light source and darkroom may be adjusted from 10 – 40 cm along the guide. Circuits are printed for better understanding the principle.

Principle and Working:
The photon energy by Einstein equation E=hn is equal to energy gap Eg between the valence and conduction bands. The energy Eg is equal to the energy barrier eV0, that electron have to overcome in going from n-doped side of diode junction to p-doped side when no external voltage V is applied to the diode.
In the p-doped side, electron recombine with holes releasing the energy Eg in the form of photon is given by equation

E_g = eV₀