Optical Pyrometer measures very high temperatures by analyzing radiation from hot bodies. Option A (Stefan's law) is wrong — Stefan's law (E=σT⁴) relates total energy to T⁴. It is used by Total Radiation Pyrometers not Optical Pyrometers. Stefan's law involves total radiation of all wavelengths. Option B (Newton's cooling law) is wrong — Newton's cooling law describes rate of heat loss proportional to temperature difference. It applies to convective cooling not to pyrometry. Option C (Wien's radiation law) is CORRECT — Optical Pyrometer works on Wien's radiation law (Wien's distribution law) which describes spectral distribution of radiation from a black body. The optical pyrometer uses the disappearing filament method: a reference filament is compared with the brightness of the target at a specific wavelength. When filament brightness matches target brightness the filament appears to disappear and temperature is read from calibrated scale. Range: 800°C to 2700°C. Option D (Planck's law) is wrong — Planck's law is the complete description of black body radiation. Optical pyrometers use Wien's approximation (valid at shorter wavelengths and higher temperatures) which is simpler for practical measurement.
FAQ
Common questions and clear answers for this topic.
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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