Most of the sources of energy we use, represent stored solar energy.

Which of the following is NOT ultimately derived from the sun's energy ?

Question

Most of the sources of energy we use, represent stored solar energy. Which of the following is NOT ultimately derived from the sun's energy ?

UnlockIAS · Accepted Answer

Correct — A, Nuclear energy. Nuclear energy is released from the binding energy of atomic nuclei — the fission of heavy nuclei such as uranium-235 and plutonium-239, or the fusion of light ones. Those heavy elements were forged in stellar processes that long predate our own Sun and were already present in the cloud from which the solar system condensed; nothing about the energy released when a uranium nucleus splits was ever put there by sunlight. Nuclear is therefore the clearest possible case of an energy source with no solar ancestry, and that is why the examiner marks it. Be honest about the item's defect, though: option (b), geothermal energy, is equally not derived from the sun. The Earth's internal heat comes from the primordial heat of accretion and core formation plus the ongoing radioactive decay of uranium, thorium and potassium-40 in the mantle and crust — again, not sunlight. On a strict reading this question has two scientifically correct answers, (a) and (b), and it has been noted as such. The commission's key marks (a), and (a) is the option to carry into the exam; the examiner's intent is plainly that nuclear energy, which is not even a natural surface flow, is the least solar of the four.

Why the other options are wrong — (b) Marked wrong by the official key, but it is not scientifically wrong: geothermal heat comes from the Earth's own interior — leftover heat from planetary accretion and core formation, plus the continuing radioactive decay of uranium, thorium and potassium-40 — and not from the sun. Treat this as a defect in the item rather than as a fact about geothermal energy. The examiner's reading is that nuclear energy, being a laboratory-scale release of nuclear binding energy rather than a natural planetary flow, is the intended 'not from the sun' option.  (c) Genuinely solar. Biomass is plant matter built by photosynthesis, in which green plants use sunlight to convert carbon dioxide and water into carbohydrates; burning firewood, crop residue, dung or biogas simply releases chemical energy that sunlight stored. Fossil fuels are the same story on a geological timescale.  (d) Genuinely solar. Winds exist because the sun heats the earth's surface unevenly — equator against poles, land against sea, day against night — producing pressure differences that air flows down. No solar heating means no pressure gradients and therefore no wind, so wind energy is stored solar energy at one remove.

Concept: Almost every energy source on Earth traces back to one of three ultimate reservoirs. The first and largest is solar radiation, which drives photosynthesis (hence biomass and, over geological time, fossil fuels), the atmospheric circulation (wind), the hydrological cycle (hydropower) and ocean thermal gradients. The second is the Earth's own internal heat — primordial heat of accretion plus radiogenic heat from decaying uranium, thorium and potassium-40 — which surfaces as geothermal energy. The third is gravitational and rotational: the Earth–Moon–Sun system's gravitational interaction with the Earth's rotation produces the tides, and so tidal energy. Nuclear fission and fusion sit outside all three as an engineered release of nuclear binding energy from elements formed in stars long before the solar system existed.

State PCS 2022 Q4 — Science & Technology PYQ with Answer

State PCS 2022 Q4 — Science & Technology PYQ with Answer