92
4.
PHOTOELECTRÏC EMISSION
EXPERIMENT 4—2
—
A STUDY or A PHOTO—VOLTAIC CELL
Purpose.—To study the current output of a photo-voltaic cell at
various light intensitiès.
Âppamz‘us.——The optical bench of experiment 4—1 may be
used or a light tight box, dead black inside (3’ X 2’ X 2’) Will serve
the purpose.
At the top, inside, is mounted a 50 C.P., 6-8 volt
auto head lamp (step—down transformer). Below, sliding up and
down on a calibrated rod about half a meter long is the photovoltaic cell. A wall galvanometer With shunt may be used to record
the currents. No batteries are used since the cell generates its own
voltage. The current delivered by the cell is dependent on the
light intensity, the external resistance, the temperature and the
previous exposure
to light-.
Experiment._—Obtain data and plot two curves on the same
graph, galvanometer deections (photo-currents) vertically and
‘
1/d2 (light interisities) horizontally; one with as low an external
—
resistance as possible (only a few ohms) and one With a few thousand ohms in series with the meter. Always wait until the currents
settle down to a fairly constant value; about 30 seconds for each
reading; longer times are required when, the light on the cell is
brighter. Why is one ”of the lines curved?
‘
_Âddiïi0ñal.—(l) If a light chopper (a slotted rotating disc) is
available, or a uctuating light source, plot relative response from
;,0 to 5000 cycles. (2) Supp0rt the cell horizontally in a thermes
-.
bottle, afew centimeters above a cooling solution. With constant
light intensity
and with c001ing solutions such as salt in ice water,
Carbon dioxide snow and liquid air, determine the relative response
;at'fvar‘ibus temperatures.
A copper—Constantin thermo—Junction
3» 0 ,t0 5 milli—voltmeter and an ice watercold
_
Junction
”the “temperature.
Calibration, data for
thesemetalsmllbefoudrn the—Handbook of Chemistry and.
Use calcmm
°h1@rldeasadrymgagent toavordthewatervapor condensedout
Ïi
°fthe alruPonthecesurface àt;hélow
4.
PHOTOELECTRÏC EMISSION
EXPERIMENT 4—2
—
A STUDY or A PHOTO—VOLTAIC CELL
Purpose.—To study the current output of a photo-voltaic cell at
various light intensitiès.
Âppamz‘us.——The optical bench of experiment 4—1 may be
used or a light tight box, dead black inside (3’ X 2’ X 2’) Will serve
the purpose.
At the top, inside, is mounted a 50 C.P., 6-8 volt
auto head lamp (step—down transformer). Below, sliding up and
down on a calibrated rod about half a meter long is the photovoltaic cell. A wall galvanometer With shunt may be used to record
the currents. No batteries are used since the cell generates its own
voltage. The current delivered by the cell is dependent on the
light intensity, the external resistance, the temperature and the
previous exposure
to light-.
Experiment._—Obtain data and plot two curves on the same
graph, galvanometer deections (photo-currents) vertically and
‘
1/d2 (light interisities) horizontally; one with as low an external
—
resistance as possible (only a few ohms) and one With a few thousand ohms in series with the meter. Always wait until the currents
settle down to a fairly constant value; about 30 seconds for each
reading; longer times are required when, the light on the cell is
brighter. Why is one ”of the lines curved?
‘
_Âddiïi0ñal.—(l) If a light chopper (a slotted rotating disc) is
available, or a uctuating light source, plot relative response from
;,0 to 5000 cycles. (2) Supp0rt the cell horizontally in a thermes
-.
bottle, afew centimeters above a cooling solution. With constant
light intensity
and with c001ing solutions such as salt in ice water,
Carbon dioxide snow and liquid air, determine the relative response
;at'fvar‘ibus temperatures.
A copper—Constantin thermo—Junction
3» 0 ,t0 5 milli—voltmeter and an ice watercold
_
Junction
”the “temperature.
Calibration, data for
thesemetalsmllbefoudrn the—Handbook of Chemistry and.
Use calcmm
°h1@rldeasadrymgagent toavordthewatervapor condensedout
Ïi
°fthe alruPonthecesurface àt;hélow