Answer to Question #151566 in Electricity and Magnetism for Iftikhar Ahmed

Question

Briefly explain the theory and procedure for the experiment to determine Plank’s constant by
Photo electric apparatus. Also write down the concluding remarks.

Answer 1

Answer

the theory and procedure for the experiment to determine Plank’s constant by

Photo electric apparatus is as follows

Step i)if the potential is small then the potential

energy at the anode is less than the kinetic energy of

the electrons and there is a current through the tube.

Step ii) if the potential is large enough the

potential energy at the anode is larger than the kinetic

energy and the electrons are driven back to the

cathode. In this case, there is no current.

Step iii) The third case is if the voltage just stops the

electrons (with maximum kinetic energy Tmax) from

reaching the anode. The voltage required to do this is called the “stopping potential" (V0). A typical I-

V characteristics for a given frequency of light is also as below.

Thus we can be rewritten as, 

$eV_0=h\nu-e\phi\\V_0=h\nu/e-\phi$

It is worth noting here that, since the anode and cathode surfaces are different, an additional 

contact potential “A” comes into the picture which simply gets added to the work function 

“Φ”. can be written in terms of wavelength as

Standard value of h is known1

 to be $6.626×10^{-34}J-s$ .