The full form of LED is
- A.Light Emitting Diode
- B.Light Emitting Device
- C.Light Enhancing Device
- D.Light Enhancing Diode
Correct answer
Explanation
The correct answer is A, Light Emitting Diode. An LED is a semiconductor p–n junction diode that gives out light when current flows through it in the forward direction.
When an LED is forward biased, electrons from the n-side meet holes on the p-side and release their extra energy as light. The colour depends on the semiconductor used, such as gallium arsenide or gallium nitride, rather than on a coloured cover. LEDs use far less power than filament bulbs, waste little energy as heat and last much longer, which is why the UJALA scheme promoted LED bulbs across India.
B is wrong because the D stands for diode, a specific two-terminal semiconductor device, not a general "device".
C is wrong because an LED produces light; it does not enhance existing light.
D is wrong for the same reason: the E stands for emitting, not enhancing.
Exam tip: LED = Light Emitting Diode; LCD = Liquid Crystal Display; LASER = Light Amplification by Stimulated Emission of Radiation.
Practice Questions
View allRecently, there was a growing awareness in our country about the importance of Himalayan nettle (Girardinia diversifolia) because it is found to be a sustainable source of
- A.anti-malarial drug
- B.biodiesel
- C.pulp for paper industry
- D.textile fibre
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The Himalayan nettle yields a strong natural fibre that can be spun and woven into cloth. Girardinia diversifolia, known as Himalayan giant nettle or allo, is a stinging shrub that grows wild in the moist forests of the Himalayas, including Uttarakhand, Himachal Pradesh and the North-east, as well as Nepal.
Read the full explanation →Which of the following statements are correct regarding the general difference between plant and animal cells ? 1. Plant cells have cellulose cell walls whilst animal cells do not. 2. Plant cells do not have plasma membrane unlike animal cells which do. 3. Mature plant cell has one large vacuole whilst animal cell has many small vacuoles. Select the correct answer using the code given below:
- A.1 and 2 only
- B.2 and 3 only
- C.1 and 3 only
- D.1,2 and 3
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Plant cells have a cellulose wall and one large central vacuole, but they do have a plasma membrane, just like animal cells.
Read the full explanation →Consider the following statements : 1. In tropical regions, Zika virus disease is transmitted by the same mosquito that transmits dengue. 2. Sexual transmission of Zika virus disease is possible. Which of the statements given above is/are correct ?
- A.1 only
- B.2 only
- C.Both 1 and 2
- D.Neither 1 nor 2
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Zika is spread mainly by the Aedes mosquito that also carries dengue, and it can pass between sexual partners. The Zika virus is a flavivirus first identified in Uganda's Zika forest in 1947.
Read the full explanation →What is the importance of using Pneumococcal Conjugate Vaccines in India ? 1. These vaccines are effective against pneumonia as well as meningitis and sepsis. 2. Dependence on antibiotics that are not effective against drug-resistant bacteria can be reduced. 3. These vaccines have no side effects and cause no allergic reactions. Select the correct answer using the code given below :
- A.1 only
- B.1 and 2 only
- C.3 only
- D.1, 2 and 3
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The vaccine protects against several pneumococcal diseases and so cuts antibiotic use, but no vaccine is free of side effects.
Read the full explanation →Which one of the following is NOT true for bleaching powder?
- A.It is used as a reducing agent in chemical industries
- B.It is used for bleaching wood pulp in paper factories
- C.It is used for disinfecting drinking water
- D.It is used for bleaching linen in textile industry
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Bleaching powder is an oxidising agent, not a reducing agent, so this statement is the false one. Bleaching powder, calcium oxychloride (CaOCl₂), is made by passing chlorine gas over dry slaked lime, Ca(OH)₂.
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