Planck's Constant By Cs Photocell

Item Code: SK054

Principle and Working:

Einstein postulated that light consists of a quantum of particles, called photon whose energy E is proportioned to the frequency n, by an equation, E = hn, where h is planck’s constant.

In this experiment, narrow band interference filters are used to select wave length. Each filter selects precisely one spectral line from the light of a high pressure mercury lamp. The monochromatic light falls on the cathode of the photocell. A capacitor, connected between cathode and anode of photocell, charged by anode, is used. Electrometer amplifier is used to measure the voltage at capacitor without current.




  • Multipurpose electrometer amplifier & power supply.
  • Cs photo cell.
  • Monochromatic light source may be used in many other experiments also.
  • Heavy, rigid and stable Optical bench (made of Al extrusion)
  • Saddle can hold rod from 8 to 15mm.

  • To determine Planck’s Constant by Cs Photocell.

  • Optical bench : Al exclusion, L = 1.5 mtr. with Scale, Triangular shape with end stop, 4 point levelling (steel screw).
  • Power supply : 2,3,4,5,6,8,10 & 12VAC full wave rectified, unsmoothed & unregulated D.C, Resettable thermal trip, Input 230 V AC,50 Hz.
  • Mercury light : Starting Voltage 470 Volts, Input Voltage 220 Source volts, 50 Hz, Lamp House 250 x 100mm (L x dia.) Aperture dia 25mm, Mercury Lamp 125W.
  • Electrometer : Input Impedance >1013 W,Input Current < 0.5pA, Output Voltage upto +10V, Output Current 5mA, (Short Circuit Protected), Output impedance <1W,Supply Voltage 12V AC.
  • Photocell : Photocell Cs, vacuum tube, Output 4 m m safety socket, Mounting rod 10mm dia.
  • Color Filter set : Red 635nm, Orange 570nm,Yellow 540nm, Green 500nm, Blue 460nm.
  • 1 Power Supply 12V AC/DC 5Amp
  • 1 Photocell
  • 1 Mercury Light Source
  • 1 Convex lens in holder
  • 1 Iris Diaphragm
  • 1 Set of Color Filters
  • 1 Set of Interference filter (optional)
  • 1 Electrometer Amplifier
  • 1 Optical bench triangular
  • 1 Fixed slider
  • 1 Accessory set (push switch, capacitor 100pF, red lead 50 & 100cm, black lead 50 & 100cm, yellow lead 50 & 100cm, earthing lead, Digital multimeter)
  • 1 Transversal slider