Measurement of Plank's
constant(h)[Millikan's experiment]
or Verification of Einstein's
photo electric equation
EXPERIMENTAL SETUP:
Fig:Verification of Einsteins Photoelectric Equation
The experiment setup consists of a
glass tube with two electrodes cathode and anode. Cathode and anode are
connected with milliammeter and voltmeter. The voltmeter measures the potential difference (p.d) across the cathode and anode
whereas milliammeter measures the current flowing through the circuit. When light
falls on the cathode surface the electrons are emitted from the cathode and
are attracted towards anode. when electrons reach anode electrons flow in the
circuit giving rise to photoelectric current(Ip).
When negative potential is given to the
anode, the electrons are retarded and finally at certain potential known as stopping
potential.. The photoelectric current becomes zero. At stopping potential, the
potential energy(eVo) balances the K.E.
of the photo electron.
By knowing the slope of the curve between f0 and f Plank's constant can be calculated.
To verify Einsteins photo electric equation Millikan used a light source of variable frequency emitting light of constant intensity. For the carious incident light frequencies 'v' determine the stopping potential .
A graph was plotted between the stopping potential and the incident frequency as above. The nature of the graph is same for all which verifies Einsteins Photoelectric Equation.
