This document discusses experiments measuring the current-voltage characteristics of a cadmium sulfide (CdS) photo resistor. The experiments aimed to measure the photocurrent (Iph) as a function of voltage (U) at constant irradiance, and as a function of irradiance at constant voltage. A photoresistor is a light-sensitive resistor made from a semiconductor like CdS, whose resistance decreases with increasing light intensity. The document outlines the experimental setup, mechanism, and results of measuring the CdS photo resistor's current-voltage polarization under different light conditions.

1. current-voltage
characteristics
of a CdS photo resistor

2. • Mohammad abdalraheem
• Edward nixson
• Awad osman
• Mohammed abdala
• Osman salah

3. Objects of the
experiments
 Measuring the photocurrent I Ph as a
function of the voltage U at a constant
irradiance .
 Measuring the photocurrent I Ph as a
function of the irradiance at a constant
voltage U.

4. Photocurrent ?
 a stream of electrons released from
a photoelectric cell by the action of
light.

5. CONTENTS :
 Introduction
 photoresistor
 Current–voltage characteristic
 Polarization of light
 Setup
 Mechanism of photo resistor
 Result
 Conclusion

6. Introduction:
 A photoresistor is made of a high
resistance semiconductor.
 depends on the amount of light
incident upon it.
 Photo resistors are:
used to make light-sensitive devices
 often made from cadmium sulfide
(CdS).

7.  The resistance of a CdS photo
resistor varies inversely to the amount
of light incident upon it.
 Its resistance will be higher at low
light levels (in the dark) and lower at
high light levels (in the light).

8.  Cadmium sulfide is the inorganic compound with
the formula CdS.
 It occurs in nature with two different crystal
structures.
 As a compound that is easy to isolate and purify,
it is the principal source of cadmium for all
commercial applications.

9. The photoresistor

10. IRRADIANC
E
 Is the power of electromagnetic
radiation per unit area (radiation flux )
of a surface.

11. CURRENT–VOLTAGE
CHARACTERISTIC

12. POLARIZATION OF LIGHT

14.  Model of an ideal photoconductor: electron-
hole pairs are produced throughout the crystal by the
external light source and undergo recombination.
Electrons leaving the crystal at the electrode (+) are
replaced with electrons entering at the electrode (-).

18. D : transparency when the
polarization planes are
parallel
Ø : The irradiance
Ø 0: irradiance without
polarization filters
cos2∞: the angle
between the polarizer

19. The CdS photo resistor behaves like an ohmic
resistance that depends on the irradiance.
The photocurrent I ph as a function of the
voltage u at constant irradiance was measuring.
The photocurrent I ph as a function of the
irradiance at constant voltage u was measuring.