What is the lower fixed point (freezing point of water) on the Kelvin scale?
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The Kelvin scale is the absolute temperature scale used in scientific calculations. Option A (0 K) is incorrect — 0 K represents absolute zero, the lowest theoretically possible temperature where all molecular motion ceases. This equals -273.15°C. Absolute zero is NOT the freezing point of water on the Kelvin scale; it is a fundamental minimum temperature. Option B (100 K) is incorrect — 100 K equals -173.15°C, which is an extremely cold temperature (below the boiling point of nitrogen at -196°C but not as cold as liquid helium). It has no special significance as the freezing point of water. Option C (273.15 K) is CORRECT — the freezing point of pure water on the Kelvin scale is 273.15 K (often approximated as 273 K in competitive exams). This corresponds to 0°C and 32°F. The Kelvin scale starts at absolute zero (0 K = -273.15°C) and its degree increments are the same size as Celsius degrees. The scale was developed by William Thomson (Lord Kelvin) in 1848. Option D (373.15 K) is incorrect — 373.15 K is the boiling point of water (100°C), not the freezing point. Freezing = 273.15 K; Boiling = 373.15 K. For exams: Water freezing = 0°C = 32°F = 273 K = 0°R.
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Heat is a form of energy that transfers between objects or systems due to a temperature difference, moving from a hotter body to a cooler one until thermal equilibrium is reached.
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