Physics & chemistry in everyday life

Answer: (a) Observation and understanding of the Universe

All four terms belong to physics and cosmology, the study of how the Universe is built and how it began. An event horizon and a singularity are parts of a black hole, and the Standard Model describes matter and its forces.

• ✓ (a) The event horizon is a black hole's boundary, inside which nothing can escape, and the singularity is the point at its centre where matter is crushed to infinite density. The Standard Model explains how the building blocks of matter interact. String theory is a physicists' theory of fundamental forces and matter. All four help us understand the Universe.
• ✗ (b) Eclipses are explained by the positions of the Sun, Earth and Moon and need none of these terms.
• ✗ (c) Launching satellites concerns rockets and orbits, not black holes or particle physics.
• ✗ (d) The origin of living organisms belongs to biology and evolution. NCERT ties 'singularity' to the Big Bang, the origin of the Universe.

Remember · Event horizon and singularity are black-hole terms; the Standard Model is particle physics; string theory is theoretical physics. All concern the Universe.

📘 Read it in NCERT: Class 11 Fundamentals of Physical Geography, Ch 2 (practise this chapter)

Question and answer: UPSC's official GS Paper I (2017, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (d) 1, 2 and 3

All three pairs are correct. Each names a chemical that has drawn regulatory or health concern in an everyday product: lead in cosmetics such as lipstick, brominated vegetable oil in soft drinks, and added monosodium glutamate (MSG) in Chinese-style fast food.

• ✓ 1. Lead is a toxic heavy metal that can turn up as a contaminant in cosmetics. Indian rules bar lead compounds as colouring in cosmetics and Indian Standards set a 20 ppm ceiling for lead.
• ✓ 2. Brominated vegetable oil (BVO) is a clouding agent that has been used in soft drinks. WHO's food-additive expert committee (JECFA) allocated it no acceptable daily intake, and FSSAI's manual carries a test to detect BVO in soft drinks.
• ✓ 3. MSG is a flavour enhancer commonly added in Chinese-style cooking. It is controversial enough that FSSAI requires a label on foods with added MSG, saying it is not recommended for infants below 12 months and pregnant women.

Remember · Lead in lipstick, brominated vegetable oil in soft drinks, MSG in Chinese fast food: all three are chemicals of health concern, so all pairs match.

Question and answer: UPSC's official GS Paper I (2017, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (c) 1, 2 and 3

All three statements are advantages of OLED displays. Each OLED pixel makes its own light, so the panel needs no rigid backlight unit as an LCD does, and it can be built thin, on flexible plastic, see-through or rolled up.

• ✓ 1. OLED layers can be deposited on flexible substrates, not only on glass, which is why bendable and foldable phone screens use them. An LCD needs a backlight and a rigid liquid-crystal cell.
• ✓ 2. Because the panel can be made on a flexible base, roll-up and wearable displays, including ones stitched into clothing, are possible. Curved, bendable, foldable and rollable OLED screens already exist.
• ✓ 3. OLEDs can be made transparent, so a see-through display is possible. An LCD depends on a backlight behind the screen, which blocks that.

Remember · OLED pixels emit their own light (no backlight), so screens can be thin, flexible, rollable and transparent. LCDs cannot do this easily.

Question and answer: UPSC's official GS Paper I (2017, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (b) To detect gravitational waves

eLISA was planned as a space-based observatory to detect gravitational waves, the ripples in space-time caused by events such as merging black holes. It works as a laser interferometer in space, so its purpose is gravitational-wave detection.

• ✓ (b) The name gives it away: a Laser Interferometer Space Antenna is a laser-based gravitational-wave detector in space, the space counterpart of ground detectors such as LIGO.
• ✗ (a) Neutrinos are detected by large underground or under-ice detectors, not by a laser interferometer in space.
• ✗ (c) A missile-defence test has nothing to do with this science mission.
• ✗ (d) Solar flares are studied by solar observatories and space-weather missions, not by an interferometer built for gravitational waves.
• • Since then The eLISA concept is now the European Space Agency's LISA mission, described as the first space-based observatory for gravitational waves, with launch planned for 2035.

Remember · eLISA/LISA = laser interferometer in space to detect gravitational waves. Ground-based cousin: LIGO, which India is joining.

📘 Read it in NCERT: Class 11 Knowledge Traditions and Practices of India, Part I, Ch 5 (practise this chapter)

Question and answer: UPSC's official GS Paper I (2017, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error