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

Answer.4. ILD emits coherent light whereas LED emits incoherent light

Explanation:-

ILD (Injection laser diode) produces coherent radiation in which the waves generated by the ILD are at the same frequency. ILD emits coherent light whereas LED emits incoherent light.

Comparison between ILD and LED is shown in the following table:

Answer.3. Light Emitting Diode

Explanation:-

LED stands for Light Emitting Diode.

LED (light-emitting diode):

• The LED (light-emitting diode) is a PN junction device that emits light when a current pass through it in the forward direction, i.e. when LED is forward biased, it emits light.
• In an LED, this energy lies in the visible region of electromagnetic radiation, and the photon released is perceived as light.
• An LED in this way converts electrical energy into light energy.
• In reverse biased mode, it works like a normal diode and does not emit light.

Answer.2. 813 Ω

Explanation:-

According to the question, we can draw circuit as:

By voltage division rule, we can write:

${V_R} = \left( {\frac{R}{{R + 20}}} \right) \times 10$

V_R = (12 × 10^-3) × R     —(2)

From equation (1) and (2), we get:

$\left( {12 \times {{10}^{ – 3}}} \right) \times R = \frac{{R \times 10}}{{R + 20}}$

12 + 10^-3 = 10/(R + 20)

12 × 10^-3 R = 9.76

R = 9.76/(12 × 10^-3) = 813.33Ω

∴ R = 813 Ω

Hence, the nearest value of the protective resistance should be 813 Ω to protect LDR.

Answer.3. 1 kΩ

Explanation:-

Source voltage = 15 V

Voltage of LED = 3 V

Current of LED = 3 mA

Now,

The given circuit can be drawn as

The current through the LED circuit must be 3 mA and the voltage drop across them is 3 V each.

Therefore, by applying KVL, we get,

15 – R (3 mA) – 3 – 3 – 3 – 3 = 0

R = (15 − 12)/3  = 1 kΩ

Answer.4. Constant Current

Explanation:-

• LED drivers are the driving force that provides and regulates the necessary power to make sure the LEDs operate in a safe and consistent manner. One important choice is that of choosing a constant current LED driver versus a constant voltage LED driver.
• 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).

Answer.2. Single-frequency

Explanation:-

A monochromatic laser emits only one wavelength i.e. single frequency & therefore reduces or does not contribute to chromatic dispersion.

Note: Monochromatic Dispersion results from the spectral width of the emitter i.e. the spectral width determines the number of different wavelengths that are emitted by the LED or laser. One way to reduce chromatic dispersion is to narrow the spectral width.

Answer.2. White

Explanation:-

1) A LED display is a flat panel display that uses an array of light-emitting diodes as pixels for a video display. 

2) LED displays can offer higher contrast ratios than a projector and are thus an alternative to traditional projection screens.

3) LED display consists of a matrix of red, green, and blue diodes.

Answer.2. Current injected

Explanation:-

• The efficiency of LEDs will be determined by the radiate recombination rate
• Temperature influence the output power of an LED through its effects on the internal quantum efficiency of the device.
• The internal quantum efficiency of LEDs decreases exponentially with increasing temperature.
• The efficiency of LED is directly proportional to the current injected.

Answer.1. White

Explanation:-

Light Emitting Diode:

• A light-emitting diode (LED) is a semiconductor light source.
• Electroluminescence is the working principle of LED.
• A light-emitting diode emits light when a current flows through it.
• Infrared LEDs are used in remote-control circuits.
• Warm white lighting fixtures are often preferred in living rooms to create a peaceful atmosphere.
• The warm white lights are a good choice to compliment earthy tones and wood furniture.
• White light is obtained by using multiple semiconductors or a layer of light-emitting phosphor on the semiconductor device.

Answer.4. Photo-diode

Explanation:-

Photo-diode is a light-sensing device that is used to sense the intensity of light. Some of the examples are the smoke detector, a receiver in tv for converting remote signals, etc.