Photoelectric Effect Apparatus
Model No. AP-8209
9
®
Experiment 1: Measuring and Calculating Planck’s
Constant,
h
Preparation before measurement
1.
Cover the window of the Mercury Light Source enclosure with the Mercury Lamp Cap from
the Optical Filters box. Cover the window of the Photodiode enclosure with the Photodiode
Cap from the Optical Filters box.
2.
On the h/e Power Supply, turn on POWER and MERCURY LAMP. On the Photoelectric
Effect Apparatus, push in the POWER button to the ON position.
3.
Allow the light source and the apparatus to warm up for 20
minutes.
4.
On the apparatus, set the VOLTAGE to –2 — +2 V. Turn the
CURRENT RANGES switch to 10
-13
.
5.
To set the current amplifier to zero, first
disconnect
the ‘A’, ‘K’,
and ‘down arrow’ (GROUND) cables from the back panel of the
apparatus.
6.
Press the PHOTOTUBE SIGNAL button in to CALIBRATION.
7.
Adjust the CURRENT CALIBRATION knob until the current is zero.
8.
Press the PHOTOTUBE SIGNAL button to MEASURE.
9.
Reconnect
the ‘A’, ‘K’, and ‘down arrow’ (GROUND) cables to the back of the
apparatus.
Measurement
1.
Uncover the window of the Photodiode enclosure. Place the 4 mm
diameter aperture and the 365 nm filter onto the window of the
enclosure. (See the sidebar note.)
2.
Uncover the window of the Mercury Light Source. Spectral lines of
365 nm wavelength will shine on the cathode in the phototube.
3.
Adjust the VOLTAGE ADJUST knob until the current on the
ammeter is zero.
4.
Record the
magnitude
of the stopping potential for the 365 nm
wavelength in Table 1.
5.
Cover the window of the Mercury Light Source.
Note:
It is very important
to allow the light source
and apparatus to warm
up for 20 minutes prior to
making any measure-
ments.
Note:
Always have a filter
on the window of the Pho-
todiode enclosure, and
put the cap on the Mer-
cury Light source when-
ever you change the filter
or aperture. Never let the
light from the Mercury
Light source shine
directly into the Photo-
diode enclosure.