Some components make use of the photovoltaic effect, which is the process of converting light to electrical energy. In a photovoltaic cell, electrons absorb the energy from light falling on a photovoltaic cell. The electrons then become free electrons.
QUESTION: What is the photovoltaic effect? (E6F04)
ANSWER: The conversion of light to electrical energy
QUESTION: What absorbs the energy from light falling on a photovoltaic cell? (E6F01)
ANSWER: Electrons
The most common type of photovoltaic cell used for electrical power generation is made from silicon, and the approximate open-circuit voltage produced by a fully-illuminated silicon photovoltaic cell is 0.5 V.
The efficiency of a photovoltaic cell is the relative fraction of light that is converted to current. In recent years, manufacturers have greatly increased the efficiency of their solar panels, making solar power feasible for many amateur radio applications.
QUESTION: What is the most common type of photovoltaic cell used for electrical power generation? (E6F10)
ANSWER: Silicon
QUESTION: What is the approximate open-circuit voltage produced by a fully illuminated silicon photovoltaic cell? (E6F11)
ANSWER: 0.5 V
QUESTION: What is the efficiency of a photovoltaic cell? (E6F09)
ANSWER: The relative fraction of light that is converted to current
Photoconductivity is a similar phenomenon. The conductivity of a photoconductive material increases when light shines on it, allowing you to use it as a sensor. Crystalline semiconductors are the most commonly-used materials for making photoconductive devices.
QUESTION: What happens to the conductivity of a photoconductive material when light shines on it? (E6F02)
ANSWER: It increases
QUESTION: Which of these materials is most commonly used to create photoconductive devices? (E6F06)
ANSWER: A crystalline semiconductor
A device that uses the phenomenon of photoconductivity is the optoisolator. Optoisolators and optocouplers consist of an an LED and a phototransistor. A current flowing through the LED causes it to emit light, which then turns on the phototransistor. These components provide electrical isolation because LED and the phototransistor are separated by a small gap and there is no electrical connection between them. 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.
QUESTION: What is the most common configuration of an optoisolator or optocoupler? (E6F03)
ANSWER: An LED and a phototransistor
QUESTION: Why are optoisolators often used in conjunction with solid-state circuits when switching 120 VAC? (E6F08)
ANSWER: Optoisolators provide a very high degree of electrical isolation between a control circuit and the circuit being switched
A similar device is the solid-state relay. A solid state relay is a circuit that acts like a relay, but uses semiconductor devices instead of a mechanical switch. To provide the electrical isolation normally provided by a mechanical relay, a solid state relay might use an optocoupler.
QUESTION: What is a solid-state relay? (E6F07)
ANSWER: A device that uses semiconductors to implement the functions of an electromechanical relay
An optical shaft encoder is another device that relies on photoconductivity. It consists of a light source, a phototransistor, and a patterned wheel. As the wheel rotates between the light source and the photo transistor, it interrupts the light source, causing the phototransistor to turn on and off. The resulting output allows a microcontroller to detect when the shaft is rotating and in which direction. One application for an optical shaft encoder is to allow a radio to detect when an operator is turning a knob.
QUESTION: Which describes an optical shaft encoder? (E6F05)
ANSWER: A device that detects rotation of a control by interrupting a light source with a patterned wheel
Edward Vielmetti says
Neat questions!
The optical shaft encoder is described on Wikipedia on the “Rotary encoder” page. You might use one of these for example to do satellite tracking. In the real world if you have high torque you have to worry about slippage. The wheel patterns give some actual utility to Gray Code, where only one bit changes state per phase transition.