Optical Sources MCQ || Optical Sources and Detector Questions and Answers

Answer.2. Detector

Explanation:-

A detector is a device or circuit that extracts information from a modulated radio-frequency current or voltage.

De-multiplexer:

• A de-multiplexer (or de-mux) is a device that takes a single input line and routes it to one of several digital output lines.
• A de-multiplexer of 2ⁿ outputs has n select lines, which are used to select which output line to send the input.
• A de-multiplexer is also called a data distributor.

Converter: A converter is an electrical circuit that accepts a DC input and generates a DC output of a different voltage, usually achieved by high frequency switching action employing inductive and capacitive filter elements.

Answer.2. It converts AC to DC

Explanation:-

An LED driver is a self-contained power supply that regulates the power required for an LED or array of LEDs.

• Constant current LED drivers are designed for a designated range of output voltages and a fixed output current (mA). LEDs that are rated to operate on a constant current driver require a designated supply of current usually specified in milliamps (mA) or amps (A).
• Constant voltage LED drivers are used for LEDs that require one stable voltage and have a current that is already regulated either via simple resistors or an internal constant current driver.

The output of LED is either constant voltage or constant current (DC).

Answer.1. Light Dependent Resistor

Explanation:-

• The Light Dependent Resistor (LDR) is made from a piece of an exposed semiconductor material such as cadmium sulfide.
• This material changes its electrical resistance from several thousand Ohms in the dark to only a few hundred Ohms when light falls upon it by creating hole-electron pairs in the material.

Answer.2. LED and LCD

Explanation:-

Active displays:

• If the visual information is presented by emitting light then that is called “Active displays”.
• A special feature for front panel receiver displays that generates animated patterns for both segmented and dot-matrix LCDs that proceed with the sequential display of information such as a clock, CD titles. Examples: CRT, LED’s, VFD, SED

Passive displays: If the visual information is presented by modulating light then that is called “Passive displays”. Examples: Liquid Crystal Displays, Digital Micromirror Device (DMD), Interferometric modulator(IMOD).

Answer.2. 1.7-3.3 V

Explanation:-

The LED (light-emitting diode) is a PN junction device that emits light when a current passes through it in the forward direction. LEDs require moderate power for their operation. A typical voltage drop of 1.7 V to 3.3 V and a current of 20 mA is required for full brightness. Therefore, LEDs are useful where miniaturization of DC power is important.

Answer.3. DC

Explanation:-

An LED driver is a self-contained power supply that regulates the power required for an LED or array of LEDs. The output of LED is either constant voltage or constant current (DC). 

• Constant current LED drivers are designed for a designated range of output voltages and a fixed output current (mA). LEDs that are rated to operate on a constant current driver require a designated supply of current usually specified in milliamps (mA) or amps (A).
• Constant voltage LED drivers are used for LEDs that require one stable voltage and have a current that is already regulated either via simple resistors or an internal constant current driver.

Answer.2. Recombination of charges takes place

Explanation:-

In LED, light is emitted due to the Recombination of charges takes place.

An LED charge carrier recombination takes place at the P-N junction when electrons from N-region recombine with the holes from P-region. Electrons from N-type semiconductors are in the higher conduction band whereas holes in P-type semiconductors area are in the lower conduction band. The transition of electrons from the conduction band to the valance band makes the emission of photons i.e. light and heat energy. Thus the emitted light comes but from the electron-hole recombination which occurs due to forward bias applied to the diode.

Answer.3. Visible region

Explanation:-

Light-emitting diodes (LEDs) are specially doped P N junction diodes, which emit light when a proper forward bias is applied across the diodes.

The LEDs fabricated by Gallium Phosphide produce visible red light and Gallium Arsenide Phosphide semiconductor produces visible red light.

Various LED and their colors are shown

Answer.1. Preventing damage against EMI 

Explanation:-

An LED driver is a self-contained power supply that regulates the power required for an LED or array of LEDs. 

LED drivers applications:

1) The change in forward voltage of LED with the change in temperature can cause the LED to burn out, this is also known as Thermal Runaway.

2) LED drivers to prevent damage to LEDs as the constant current LED driver compensates for the changes in the forward voltage while delivering a constant current to the LED.

3) Thus LED drivers, convert higher voltage, alternating current to low voltage, direct current, and

4) It keeps the voltage or current flowing through the circuit at its rated level.

Answer.3. PIN diode

Explanation:-

• PIN photodiodes are used in fibre optic network cards and switches.
• They are designed to detect photons and are used in optical detection.
• Reverse current flows through the photodiode when it is sensing light.
• When photons excite carriers in a reverse-biased p-n junction, a very small current proportional to the light intensity starts to flow.
• The intensity depends on the wavelength of the light.
• Photodiodes convert incident light into electric energy, so they are used as optical detectors.