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An Optical Pyrometer measures very high temperatures by analysing the radiation emitted by a hot body. Option A (Stefan's law) is incorrect — Stefan's law relates total energy radiation to T⁴. While Stefan's law is related to radiation, the Optical Pyrometer does not use total radiation. It specifically analyses the spectral (wavelength-specific) component of radiation. Total Radiation Pyrometers are based on Stefan's law, not Optical Pyrometers. Option B (Newton's law of cooling) is incorrect — Newton's law of cooling states that the rate of heat loss is proportional to the temperature difference between the body and surroundings. It applies to convective cooling at modest temperature differences, not to high-temperature pyrometry. Option C (Wien's radiation law) is CORRECT — Optical Pyrometers work on Wien's radiation law (also called Wien's distribution law). This law describes the spectral distribution of radiation from a black body. This method is called optical pyrometry or disappearing filament method. Option D (Planck's law) is incorrect — while Planck's law is the complete description of black body radiation, optical pyrometers specifically use Wien's approximation (valid at shorter wavelengths and higher temperatures) for practical measurement.
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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.
