Prelims · Science & technology · 28 questions

Physics & chemistry in everyday life

Every UPSC Prelims question on this topic, 2016–2026, newest first. Tap an option to check yourself; the answer and explanation open below it.

Asked in 8 of 11 years · most in 2021 (4)

UPSC syllabus: “General Science.” See the full syllabus →

Prelims 2020 · Q39

Medium

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:

Answer & explanation

Answer: (c) 1, 3 and 4 only

VLC sends data by rapidly varying visible light, roughly 380 to 780 nm in wavelength, from LEDs. It is a high-speed, indoor, short-range technology, so statement 2 (long-range) is the wrong one; the other three statements are correct.

✓ 1. VLC works in the visible part of the spectrum, taken as about 380-780 nm in the ITU standard; UPSC's 375 nm lower limit is a marginal variation of the same band.
✗ 2. VLC is designed for high-speed indoor, in-premises use, not for long-range links. It is short-range optical wireless communication.
✓ 3. Light offers a far wider bandwidth than radio waves, and a peer-reviewed review lists a higher transmission rate and high bandwidth among VLC's advantages over radio-frequency links, which is why it can carry large amounts of data faster than Bluetooth.
✓ 4. UPSC's key counts this as correct: VLC carries data on light, not on radio waves, so it is not subject to radio-frequency electromagnetic interference (the review lists reduced interference among VLC's advantages over radio).

Remember · VLC (Li-Fi) = data on visible light (about 380-780 nm): fast, short-range, indoor, free of radio interference.

Sources

ITU-T Recommendation G.9991 (03/2019), High-speed indoor visible light communication transceiver ↗ “Two wavelength bands are defined in this Recommendation, which are visible light (380 nm-780 nm) and infrared (800 nm-1675 nm). … transceivers for in-premises applications designed for the high-speed optical wireless transmission of data using visible light and infrared communications.”
Recent Advances in Micro-LEDs for Visible Light Communications (review article, PubMed Central) ↗ “VLC has become more popular recently because of its many advantages over conventional radio frequencies, including a higher transmission rate, high bandwidth, low power consumption, fewer health risks, and reduced interference.”

Question and answer: UPSC's official GS Paper I (2020, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 1 Oct 2026 (how we verify). Permalink ·

Prelims 2020 · Q41

Hard

With reference to carbon nanotubes, consider the following statements:

1.They can be used as carriers of drugs and antigens in the human body.
2.They can be made into artificial blood capillaries for an injured part of human body.
3.They can be used in biochemical sensors.
4.Carbon nanotubes are biodegradable.

Which of the statements given above are correct?

Answer & explanation

Answer: (c) 1, 3 and 4 only

Carbon nanotubes are tiny hollow tubes of rolled-up carbon sheets that are used in medicine to carry drugs and in biochemical sensors, and living systems can break them down with enzymes. Making artificial blood capillaries from them is not an established use, so statement 2 is the one that fails.

✓ 1. Carbon nanotubes are used as carriers, for example to deliver drugs and other payloads in the body, and are studied for bioimaging as well.
✗ 2. The established medical uses are bioimaging, drug delivery and biosensing. Building artificial blood capillaries for an injured body part is not one of them.
✓ 3. Biosensing is one of the main biomedical uses of functionalised carbon nanotubes.
✓ 4. Enzymes such as peroxidases can degrade carbon nanotubes, so they can be cleared from the body after delivering their payload; research is now focused on this route.

Remember · Carbon nanotubes: drug carriers and biosensors, and enzyme-degradable; not used as artificial blood capillaries.