Objectives: 1) To determine an experimental value
for Planck’s constant.
2) To
determine the work function of the metal in the photo-sensor.
Theory: In order to determine an
experimental value for Planck’s constant, we must combine a number of theories
and equations about the photoelectric effect that we learned in class. Max Planck created the first of these in 1900.
Eq1: 
This formula states that the size of a quantum of energy
equals the frequency of the oscillator or the inverse of the wavelength multiplied by Planck’s constant.
The next principle involved comes from Einstein himself. He theorised that, to release an electron
through the photoelectric effect, a mininmum energy was required. He called this the work function.
Eq 2: 
Any extra energy given to the electron by the photon
would be expressed in the form of kinetic energy. Combining this fact with Eq 2 gives:
Eq3: 
Where 
is the charge of 1 proton
and 
is the retarding potential
that eliminates all current.
Combining Eq 3 with Eq 1 gives a new equation that can
be used to compare the wavelength of the incident light with the retarding
potential:
Eq 4: 
This
equation can be simplified into a linear relation:
Eq 5: 
Where
the slope is 
and the y-intercept is 
.
Data:
Data Analysis:
Results: Planck’s
Constant
Work
Function
Cutoff
Wavelength
Uncertainty:
Due to the incredibly small value of Planck’s constant,
an accurate experimental value is nearly impossible with the instruments we
were using. Since the precision of the equipment
is beyond our control, we have an acceptable uncertainty of between 50 and 100
%. So long as our experimental value is
of the correct magnitude, we will consider this experiment a success and our
theories verified.
Conclusion:
