RRB NTPC Science and Technology Basics 2 — Questions and Answers

Question 1: Which of the following is an example of a chemical change?

Melting of ice
Dissolving sugar in water
Burning of wood (Correct answer)
Cutting of paper

Correct answer: Burning of wood

Burning of wood is a chemical change (combustion) because new substances (CO₂, water vapor, ash) are formed and the change is irreversible.

Physical change vs. Chemical change: Physical changes alter the form/state but not the chemical composition (reversible): Melting ice (H₂O solid → liquid), dissolving sugar (sugar molecules still intact), cutting paper (still cellulose). Chemical changes form new substances with different properties (generally irreversible): Burning wood (cellulose + O₂ → CO₂ + H₂O + ash), rusting iron (Fe + O₂ → Fe₂O₃), cooking food, souring of milk. Signs of a chemical change: color change, gas production, heat/light released or absorbed, precipitate formation, change in smell. Burning wood releases CO₂ and water vapor, leaving ash (carbon residue) — completely different from the original wood.

Question 2: The unit of electrical resistance is:

Ampere
Volt
Ohm (Correct answer)
Watt

Correct answer: Ohm

The SI unit of electrical resistance is the Ohm (symbol: Ω), named after German physicist Georg Simon Ohm who formulated Ohm's Law.

Electrical units: Resistance — Ohm (Ω), after Georg Ohm; Current — Ampere (A), after André-Marie Ampère; Voltage/Potential difference — Volt (V), after Alessandro Volta; Power — Watt (W), after James Watt; Energy — Joule (J) or kilowatt-hour (kWh); Capacitance — Farad (F); Inductance — Henry (H); Frequency — Hertz (Hz). Ohm's Law: V = IR (Voltage = Current × Resistance). Power = V × I = I²R = V²/R. In household circuits: a 100W bulb connected to 220V has resistance = V²/P = 220²/100 = 484 Ω.

Question 3: Which planet has the most moons in our solar system?

Jupiter
Saturn (Correct answer)
Uranus
Neptune

Correct answer: Saturn

Saturn has the most confirmed moons in our solar system, with 146 confirmed moons as of 2023, surpassing Jupiter's 95 moons.

Moon counts as of 2023-2024: Saturn — 146 moons (now the most); Jupiter — 95 moons (previously held the record); Uranus — 28 moons; Neptune — 16 moons; Mars — 2 moons (Phobos and Deimos); Earth — 1 moon; Venus and Mercury — no moons. Saturn's largest moon is Titan (larger than Mercury), which has a thick nitrogen atmosphere and methane lakes. Jupiter's largest moons (Galilean moons) are Io, Europa, Ganymede, and Callisto — discovered by Galileo in 1610. Ganymede is the largest moon in the solar system, larger than Mercury. Note: Moon counts change frequently as new small moons are discovered.

Question 4: The process by which plants make food using sunlight is called:

Respiration
Transpiration
Photosynthesis (Correct answer)
Osmosis

Correct answer: Photosynthesis

Photosynthesis is the process by which green plants, algae, and some bacteria use sunlight, water, and CO₂ to produce glucose and oxygen.

Photosynthesis: 6CO₂ + 6H₂O + Light energy → C₆H₁₂O₆ (glucose) + 6O₂. This process occurs in chloroplasts, specifically using chlorophyll (the green pigment) to capture light energy. Two stages: Light reactions (in thylakoids) — capture light energy, split water, produce ATP and NADPH, release O₂; Dark reactions/Calvin Cycle (in stroma) — use ATP and NADPH to fix CO₂ into glucose. Photosynthesis is the foundation of most food chains on Earth. Related processes: Respiration (reverse of photosynthesis — breaks down glucose to release energy); Transpiration (loss of water vapor through stomata); Osmosis (movement of water through semi-permeable membrane).

Question 5: Which type of mirror is used in the headlights of vehicles?

Plane mirror
Convex mirror
Concave mirror (Correct answer)
Both plane and convex mirror

Correct answer: Concave mirror

Concave (converging) mirrors are used in vehicle headlights. The light source is placed at the focal point, and the reflected beam comes out as a parallel, focused beam of light.

Concave mirrors are used in vehicle headlights because when a light source is placed at the focal point of a concave mirror, the reflected rays emerge as a strong, parallel beam of light. Mirror uses: Concave mirror — vehicle headlights, searchlights, telescopes (reflecting), solar cookers, ENT examination, shaving mirrors (magnification). Convex mirror — rear-view mirrors in vehicles (gives wider field of view, though images appear smaller). Plane mirror — regular mirrors, periscopes. Key property: Convex mirrors always form virtual, erect, diminished images. Concave mirrors can form both real and virtual images depending on object position.

Question 6: What is the SI unit of frequency?

Newton
Joule
Hertz (Correct answer)
Pascal

Correct answer: Hertz

The SI unit of frequency is the Hertz (Hz), named after physicist Heinrich Hertz. 1 Hz = 1 cycle per second.

Frequency is the number of cycles per unit time. SI unit = Hertz (Hz) = 1 cycle per second, named after German physicist Heinrich Rudolf Hertz (who proved the existence of electromagnetic waves in 1887). Common frequency values: Human hearing range: 20 Hz to 20,000 Hz; Ultrasound: > 20,000 Hz (used in medical imaging, sonar); Infrasound: < 20 Hz; FM Radio: 87.5–108 MHz; Mobile 4G: ~700 MHz–2.7 GHz; 5G: up to 100 GHz. Relationship with time period: f = 1/T (frequency = 1/time period). Other SI units: Newton (force), Joule (energy), Pascal (pressure), Watt (power), Ampere (current), Kelvin (temperature).

RRB NTPC Science and Technology Basics 2

Which of the following is an example of a chemical change?