|
|
Experiment
to estimate the value of Planck's Constant
using the
Photo-Electric Effect
| 1.
Preparation: |
a) |
Revise
the basic ideas of quantum theory, especially Einstein's
photo-electric equation. |
|
b) |
See
below. |
| 2. |
In this
method, light is allowed to reach a photo-emissive surface
(inside a "photo-cell"). This causes electrons to be
emitted with a range of kinetic energies. A "stopping
voltage" is then used to stop even the most energetic of
the emitted electrons before they reach the cathode of the
photo-cell. A simplified diagram of the apparatus is shown
below. |
|
|
|
Find the voltage, Vs,
needed to reduce the reading of the galvanometer to zero with a
range of different frequencies of light, f, reaching the
photo-cell (different coloured filters).
|
|
Einstein’s photo-electric equation
can be stated as
|
|
|
eVs = hf
– W
|
|
Use this to find a value of Planck’s
constant, h.
|
|
© David
Hoult 2008 |
The
Open Door Web Site