E6F06 (A)
Which of these materials is affected the most by photoconductivity?
A. A crystalline semiconductor
B. An ordinary metal
C. A heavy metal
D. A liquid semiconductor

E6F: Optical components: photoconductive principles and effects,

photovoltaic systems, optical couplers, optical sensors, and optoisolators;


Some components make use of the photovoltaic effect. The photovoltaic effect is the conversion of light to electrical energy. (E6F04) In a photovoltaic cell, electrons absorb the energy from light falling on a photovoltaic cell. (E6F12) The electrons then become free electrons.

The most common type of photovoltaic cell used for electrical power generation is silicon. (E6F10)

The approximate open-circuit voltage produced by a fully-illuminated silicon photovoltaic cell is 0.5 V.

(E6F11) The efficiency of a photovoltaic cell is the relative fraction of light that is converted to current. (E6F09)

Photoconductivity is a similar phenomenon. Photoconductivity is the increased conductivity of an illuminated semiconductor. (E6F01) The conductivity of a photoconductive material increases when light shines on it. (E6F02) A crystalline semiconductor is the material that is affected the most by photoconductivity. (E6F06)

A device that uses the phenomenon of photoconductivity is the optoisolator. The most common configuration of an optoisolator or optocoupler is an LED and a phototransistor. (E6F03)

Optoisolators are often used in conjunction with solid state circuits when switching 120 VAC because optoisolators provide a very high degree of electrical isolation between a control circuit and the circuit being switched. (E6F08)

A similar device is the solid-state relay. A solid state relay is a device that uses semiconductor devices to implement the functions of an electromechanical relay. (E6F07)

Optical shaft encoders are another device that rely on photoconductivity. An optical shaft encoder is

a device which detects rotation of a control by interrupting a light source with a patterned wheel.

(E6F05) Optical shaft encoders are used to detect when an operator turns a knob on an amateur radio transceiver.

Liquid crystal displays

A liquid crystal display (LCD) is a display utilizing a crystalline liquid and polarizing filters which becomes opaque when voltage is applied. (E6F13) One thing that is true of LCD displays is that they may be hard to view through polarized lenses. (E6F14)