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Q69 (IAS/2020) Science & Technology › ICT, AI, Cybersecurity & Emerging Tech › Wireless communication technologies Official Key

With reference to Visible Light Communication (VLC) technology, which of the following statements are correct ? 1. VLC uses electromagnetic spectrum wavelengths 375 to 780 nm. 2. VLC is known as long-range optical wireless communication. 3. VLC can transmit large amounts of data faster than Bluetooth. 4. VLC has no electromagnetic interference. Select the correct answer using the code given below :

Result
Your answer: —  ·  Correct: C
Explanation

The correct answer is Option 3 (1, 3 and 4 only). The explanation for each statement is as follows:

  • Statement 1 is correct: VLC operates in the visible light spectrum, typically ranging from 375 to 780 nm (corresponding to frequencies of 400–800 THz), which is higher than the radio frequency spectrum.
  • Statement 2 is incorrect: VLC is a short-range optical wireless communication technology (often called Li-Fi). Light waves cannot penetrate walls and are easily obstructed, making it unsuitable for long-range applications.
  • Statement 3 is correct: Due to its high frequency and wide bandwidth, VLC can transmit data at speeds exceeding 1 Gbps, which is significantly faster than Bluetooth (limited to 1–3 Mbps).
  • Statement 4 is correct: VLC uses light waves rather than radio waves; therefore, it does not suffer from electromagnetic interference (EMI), making it ideal for sensitive environments like hospitals or aircraft cabins.
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PROVENANCE & STUDY PATTERN
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Don’t just practise – reverse-engineer the question. This panel shows where this PYQ came from (books / web), how the examiner broke it into hidden statements, and which nearby micro-concepts you were supposed to learn from it. Treat it like an autopsy of the question: what might have triggered it, which exact lines in the book matter, and what linked ideas you should carry forward to future questions.
Q. With reference to Visible Light Communication (VLC) technology, which of the following statements are correct ? 1. VLC uses electromagnet…
At a glance
Origin: Mixed / unclear origin Fairness: Low / Borderline fairness Books / CA: 0/10 · 0/10
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This is a classic 'Derived Tech' question. It looks like obscure Current Affairs, but it is actually solvable using Class 10 Physics (Properties of Light). The strategy is not to memorize wavelengths of every tech, but to apply 'First Principles': Light travels in straight lines, is blocked by walls, and carries more energy/data than radio waves.

How this question is built

This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.

Statement 1
What electromagnetic wavelength range does Visible Light Communication (VLC) use?
Origin: Weak / unclear Fairness: Borderline / guessy
Indirect textbook clues
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 21: Horizontal Distribution of Temperature > Insolation > p. 282
Strength: 5/5
“• Insolation is the amount of sun's energy received in the form of radiation by the earth. It is measured as the amount of solar energy received per square centimetre per minute.• Earth receives the sun's radiation in the form of short waves (visible light or wavelengths below visible light — most of it is ultraviolet radiation) which are electromagnetic.• The earth absorbs short wave radiation during daytime and reflects the heat received into space as long-wave radiation (mostly infrared radiation which is nothing but heat) during the night.”
Why relevant

Explicitly names visible light as 'short waves' of the Sun's radiation and contrasts visible with ultraviolet and infrared bands, placing visible light within the electromagnetic spectrum.

How to extend

A student could use a standard EM-spectrum chart to read off the wavelength band labelled 'visible' and thus infer the range VLC would use.

Science , class X (NCERT 2025 ed.) > Chapter 10: The Human Eye and the Colourful World > 10.6.2 Why is the colour of the clear Sky Blue? > p. 169
Strength: 4/5
“The molecules of air and other fine particles in the atmosphere have size smaller than the wavelength of visible light. These are more effective in scattering light of shorter wavelengths at the blue end than light of longer wavelengths at the red end. The red light has a wavelength about 1.8 times greater than blue light. Thus, when sunlight passes through the atmosphere, the fine particles in air scatter the blue colour (shorter wavelengths) more strongly than red. The scattered blue light enters our eyes. If the earth had no atmosphere, there would not have been any scattering. Then, the sky would have looked dark.”
Why relevant

Gives a comparative rule that red light has a longer wavelength than blue (≈1.8×), identifying visible light as a band containing distinct colours with different wavelengths.

How to extend

Combine this pattern with a colour-to-wavelength table (blue to red span) to estimate the numerical wavelength limits for visible light relevant to VLC.

Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 21: Horizontal Distribution of Temperature > Transparency of Atmosphere > p. 283
Strength: 3/5
“• Aerosols (smoke, soot, pollen), dust, water vapour, clouds etc. affect transparency.• If the wavelength of the radiation is more than the radius of the obstructing particle (such as a gas), scattering of radiation takes place. Most of the light received by earth is scattered light. If the wavelength is less than the obstructing particle (such as a dust particle), then reflection takes place.• Absorption of solar radiation takes place if the obstructing particles happen to be water vapour, ozone molecules, carbon dioxide molecules or clouds (Greenhouse effect).”
Why relevant

States a general scattering rule linking wavelength to interaction with particles (wavelength vs particle radius), implying wavelength is a defining physical property of 'light' relevant for communication channels.

How to extend

Use the scattering rule plus known particle sizes (or charts) to confirm that the band used in VLC behaves like visible light in atmospheric scattering, consistent with the visible band on the EM spectrum.

Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 13: Plant Diversity of India > 13.2.1. Fntensity of light on growth of plants > p. 197
Strength: 3/5
“ua vF:/\ r*/ :;' :E|E::T i 0l.!l • Out of 7 colours in the visible part of spectrum, only red and blue are effective in photosynthesis. • Plants grown in blue light are smaller, red light results in elongation of cells resulting in etiolated plants. Plants grown in ultraviolet and violet light are small.”
Why relevant

Refers to '7 colours in the visible part of spectrum' and distinguishes visible from ultraviolet, reinforcing that visible light is a defined segment of the EM spectrum.

How to extend

A student could map those seven colours to standard wavelength intervals to determine the span VLC would occupy.

Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 5: Environmental Pollution > 5.8.r. Causes > p. 81
Strength: 2/5
“• r Most sources of visible light (except lasers) emit light in various directions, potentially allowing it to scatter into the atmosphere. • o In urban environments, nearly all surfaces have the ability to reflect light, causing a portion of downward-directed light to bounce back upwards, further contributing to the problem of nighttime light pollution.”
Why relevant

Notes 'Most sources of visible light' and discusses scattering/reflection of visible light, linking practical light sources to the visible portion of the spectrum used in lighting and thus in optical communication.

How to extend

Relate common light sources used in VLC (LEDs, lamps) to the visible spectral band from lighting specifications to infer the communication wavelength range.

Statement analysis

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Statement analysis

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Statement analysis

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SIMILAR QUESTIONS

IAS · 2002 · Q69 Relevance score: 3.46

Consider the following statements: 1. Light of longer wavelength is scattered much more than the light of shorter wavelength. 2. The speed of visible light in water is 0.95 times and speed in vacuum. 3. Radio waves are produced by rapidly oscillating electrical currents. 4. To detect the over speeding vehicles, police use the Doppler effect of reflected short radio waves Which of these statements are correct ?

IAS · 2016 · Q5 Relevance score: 3.44

With reference to 'LiFi', recently in the news, which of the following statements" is/are correct? 1. It uses light as the medium for high-speed data transmission. 2. It is a wireless technology and is several times faster than. 'WiFi'. Select the correct answer using the code given below.

NDA-II · 2018 · Q40 Relevance score: 3.40

Consider the following statements about visible light, UV light and x-rays : 1. The wavelength of visible light is more than that of X-rays 2. The energy of X-rays photons is higher than that of UV light photons. 3. The energy of UV light photons is less than that of visible light photons. Which of the statements given above is/are correct?

NDA-II · 2015 · Q31 Relevance score: 3.06

Which one of the following statements is not correct?

IAS · 2015 · Q32 Relevance score: 3.02

With reference to 'Near Field Communication (NFC) Technology', which of the following statements is/are correct? 1. It is a contactless communication technology that uses electromagnetic radio fields. 2. NFC is designed for use by devices which can be at a distance of even a metre from each other. 3. NFC can use encryption when sending sensitive information. Select the correct answer using the code given below.