Light Emitting Diode Questions

---

Very Short Answers Questions [1 Mark Questions]

Ques. Which of the following materials can be used to produce infrared LED?

1. CdS
2. Si
3. PbS
4. GaAs

Ans. The correct answer is d. GaAs

Explanation: The energy band gap in GaAs is 1.4 eV. It is capable of producing infrared LEDs. Other combinations can be used to produce LEDs of various colors.

Ques. A light-emitting diode is

1. Lightly doped
2. Zener diode
3. Heavily doped
4. Intrinsic semiconductor

Ans. The correct answer is c. Heavily doped

Explanation: LEDs, or light-emitting diodes, are heavily doped. It operates in a forward-biased configuration. When electrons recombine with holes, the energy released in the form of photons allows light to be produced.

Ques. What should be the band gap of the semiconductors to be used as LED?

1. 1.8 eV
2. 0.5 eV
3. 1.5 eV
4. 1 eV

Ans. The correct answer is a. 1.8 eV

Explanation: Semiconductors with band gaps close to 1.8 eV are ideal LED materials. They are created from semiconductors such as GaAs, GaAsP, and others.

Ques. Which process of the Electron-hole pair is responsible for emitting light?

1. Diffusion
2. Recombination
3. Generation
4. Movement

Ans. The correct answer is b. Recombination

Explanation: When electrons recombine with holes, energy is released in the form of a photon. This photon is responsible for light emission.

Ques. The reverse breakdown voltage of LED is very low.

1. True
2. False

Ans. The correct answer is a. True

Explanation: LEDs have relatively low reverse breakdown voltages, generally about 5 V. Therefore, if access voltage is supplied, they will be fused.

Ques. What should be the biasing of the LED?

1. Forward bias then Reverse bias
2. Reverse bias
3. No biasing required
4. Forward bias

Ans. The correct answer is d. Forward bias

Explanation: The LED operates when the p-n junction is forward-biased, which means that the p-side is connected to the positive terminal and the n-side is connected to the negative terminal.

Ques. Which of the following is not a characteristic of LED?

1. High Warm-up time
2. Fast action
3. Low operational voltage
4. Long life

Ans. The correct answer is a. High Warm-up time

Explanation: Warm-up time should be lowered so that lighting activity may occur more quickly. This is one of the advantages of LED over incandescent bulbs.

Ques. What is the bandwidth of the emitted light in an LED?

1. 100 nm to 500 nm
2. 10 nm to 50 nm
3. 1 nm to 10 nm
4. 50 nm to 100 nm

Ans. The correct answer is b. 10 nm to 50 nm

Explanation: The wavelength range of the emitted light is 10 nm to 50 nm. Therefore, the radiated light is nearly (but not quite) monochromatic.

Ques. Which of the following produces the current when it absorbs photons?

1. Photodiode
2. Transducer
3. LED
4. LCD

Ans. The correct answer is a. Photodiode

Explanation: A photodiode is a device that produces electricity by absorbing light.

---

Short Answers Questions [2 Marks Questions]

Ques. What is a light-emitting diode?

Ans. A light-emitting diode is a PN junction diode that produces light when electric current flows through it in the forward direction. In this diode, charge carriers such as holes from the P-side and electrons from the N-side recombine to emit energy in the form of light or heat.

Ques. What is a diode?

Ans. A diode is a two-terminal electrical component that usually conducts electricity in one direction. It has low resistance in one direction and strong resistance in the other.

Ques. What determines the color of an LED?

Ans. The material used in the semiconducting element determines the color of an LED. Aluminum gallium indium phosphide alloys and indium gallium nitride alloys are the two basic materials utilized in LEDs. Aluminum alloys produce red, orange, and yellow light, whereas indium alloys produce green, blue, and white light. The color of the emitted light changes as the composition of these alloys changes.

Ques. What is an LCD?

Ans. A liquid-crystal display is a flat-panel display or other electronically controlled optical device that uses the light-modulating characteristics of liquid crystals together with polarizers. Liquid crystals do not emit light directly but rather need a backlight or reflector to generate color or monochrome images.

Ques. Explain the characteristics of an LED.

Ans. LEDs are semiconductor light sources that generate light when an electric current travels through them. Because of their lower power consumption, longer lifespans, and higher lighting, these diodes are commonly used. LEDs are manufactured in different shapes and are divided into many categories.

Ques. What is a Bi-colour LED?

Ans. Bi-color LED lights combine two light-emitting diodes into a single unit. The wiring is inversely parallel, with one diode oriented forward and another oriented backward, resulting in one diode being illuminated at a time. The current flow alternates between the two diodes, causing the color to change.

Ques. What are the different types of LED?

Ans. The different types of LEDs are

• Gallium Phosphide (GaP): red, yellow and green
• Gallium Nitride (GaN): green, emerald green
• Aluminium Gallium Phosphide (AlGaP): green
• Zinc Selenide (ZnSe): blue
• Gallium Arsenide (GaAs): infrared
• Gallium Arsenide Phosphide (GaAsP): red to infrared, orange
• Aluminium Gallium Arsenide Phosphide (AlGaAsP): high-brightness red, orange-red, orange, and yellow
• Silicon Carbide (SiC): blue as a substrate
• Gallium Indium Nitride (GaInN): near ultraviolet, bluish-green and blue

Ques. What is electroluminescence?

Ans. Electroluminescence is an optical and electrical phenomenon in which a substance generates light in response to an electric current or a strong electric field passing through it.

Ques. What is the operating principle of diode laser?

Ans. Diode lasers operate on the stimulated emission principle. An incident photon interacts with an excited atom, causing it to produce a photon with the same wavelength, phase, and direction as the incident photon. This process amplifies the light beam.

Ques. What is a Through-hole LED?

Ans. Through-hole LED (Light Emitting Diode) is a form of LED that is installed on a circuit board by inserting leads through holes in the board. These are utilized in situations where the LED must be more robust, such as outdoor illumination or vehicle lighting.

Also check:

---

Long Answers Questions [3 Marks Questions]

Ques. What are the advantages of light-emitting diodes?

Ans. The following are the advantages of light-emitting diodes

• Long lifespan: When compared to the ordinary incandescent bulb, the lifespan of an LED light is significantly greater.
• Energy efficient: light-emitting diodes (LEDs) are very energy efficient. They use up to 90% less energy than traditional incandescent bulbs, and they last up to 25 times longer.
• Environmentally friendly: LEDs do not contain mercury, a dangerous substance that is damaging to both human health and the environment.
• Small size: LEDs are smaller in size. Therefore, they can be used in almost any application.

Ques. What are the disadvantages of light-emitting diodes?

Ans. The following are the disadvantages of light-emitting diodes

• Initial cost: LEDs have a higher initial cost than conventional bulbs, but they can save money in the long term through energy and maintenance savings.
• Limited dimming range: Some LED lights may not work with standard dimmer switches or may have a limited dimming range.
• Quality variability: There can be significant differences in the quality and performance of different LED products. This is because LEDs are made from a variety of different materials and components, and the quality of these materials and components can vary widely.
• Color temperature issues:  LEDs may produce a cooler, more blue-toned light compared to traditional bulbs. Some people prefer the cooler, more blue-toned light of LEDs, while others prefer the warmer, more yellow-toned light of traditional bulbs.

Ques. What is the difference between a diode and an LED?

Ans. The following are the differences between a diode and an LED

---

Very Long Answers Questions [5 Marks Questions]

Ques. What are the applications of light-emitting diodes?

Ans. The following are the applications of light-emitting diodes

• LED bulbs are used in houses and industries for lighting purposes.
• Light-emitting diodes are used in bikes and automobiles.
• These are used for displaying messages on mobile phones.
• Because of their small size, minimum maintenance needs, and low energy consumption, LEDs are used as status indicators and displays on a variety of equipment and installations. 
• Large-area LED displays are used in stadium displays, dynamic decorative displays, and dynamic message signs on roads.
• LEDs are used in car brake lights and turn signals. This is due to its durability, short switching times, and visibility in intense sunlight due to its high brightness and focus.
• LEDs are commonly utilized in optical fiber and free space optics communications because their light can be rapidly controlled.

Ques. Describe the working of light-emitting diodes (LEDs).

Ans. The working principle of a light-emitting diode is mostly determined by quantum theory. 

• According to this theory, as the energy of an electron decreases from its maximum value to its minimum value, it releases energy in the form of photons that is comparable to the difference between two levels such as higher and lower.
• The connecting of a light-emitting diode can be done in the forward-biased configuration, which permits current to flow in the forward direction. 
• The current flow will be available because of the movement of electrons in the opposite direction. 
• The recombination shows that electrons moving from conduction to valence produce electromagnetic energy in the form of photons. 
• The energy of photons is comparable to the distance between the two bands of conduction and valence. 
• The light-emitting diode works on the basis of a two-terminal PN-junction semiconductor diode. 
• When triggered, it emits light. When a suitable voltage is applied to the LED terminals, electrons recombine with holes in the device, producing energy in the form of photons. 
• This type of action is known as electroluminescence, and the light color may be determined by the bandgap energy of the semiconductor.

Ques. What is the difference between LED and LCD?

Ans. The following are the differences between an LED and an LCD

---

Previous Year Questions

1. Extraction of metal from the ore cassiterite involves...[JEE Advanced 2011]
2. Commonly used vectors for human genome sequencing are...[NEET UG 2014]
3. Interfascicular cambium and cork cambium are formed due to​..
4. Pneumotaxic centre is present in​...[UP CPMT 2007]
5. Reaction of HBr with propene in the presence of peroxide gives….[NEET UG 2004]
6. Assuming the expression for the pressure exerted by the gas on the walls of the container, it can be shown that pressure is...[MHT CET 2016]
7. Which among the following is the strongest acid?...[TS EAMCET 2017]
8. Isopropyl alcohol on oxidation forms​..
9. A vector is not changed if​..
10. Which of the following arrangements does not represent the correct order of the property stated against it?...[JEE Main 2013]

For Latest Updates on Upcoming Board Exams, Click Here: https://t.me/class_10_12_board_updates

---

Check-Out: