When heat is radiated from a hot source, the amount of heat received by a nearby body depends on its emissivity.判断题
A
True
B
False

Question

When heat is radiated from a hot source, the amount of heat received by a nearby body depends on its emissivity.

BlackTom AI · Accepted Answer

Absorbed radiative heat is determined by the body’s absorptivity at the wavelengths of the incoming radiation, not by its emissivity. Key concepts: absorptivity α is the fraction of incident radiation a surface absorbs; emissivity ε is the efficiency with which a surface emits its own thermal radiation; Kirchhoff’s law states that at a given wavelength and direction, ε = α for a material in thermodynamic equilibrium, but absorption of incoming radiation is described directly by α. Geometry (view factor), distance, incident flux and spectral match also matter.

Step-by-step reasoning:
1. If a surface receives incident radiative flux G (W/m²), the absorbed flux per unit area is q_abs = α · G. For area A the total absorbed power is Q_abs = α · G · A.
2. Emission from that surface is Q_emit = ε · σ · T^4 · A (for a gray surface at temperature T), where σ is the Stefan–Boltzmann constant.
3. The amount received from an external hot source therefore depends on G (set by the source, distance, view factor and spectrum) and on α of the receiver at the source’s wavelengths. Emissivity ε governs how much the receiver emits, not how much it absorbs, unless you invoke Kirchhoff’s law to equate ε and α at the same wavelength for equilibrium conditions.
4. Example: If a hot lamp produces G = 1000 W/m² at the object’s surface and the object’s absorptivity at those wavelengths is α = 0.2, then q_abs = 0.2 × 1000 = 200 W/m². If the object’s emissivity (at its own thermal wavelengths) is 0.8, that does not change the 200 W/m² incoming absorption.

Why “True” is incorrect: stating the received heat “depends on its emissivity” confuses emission and absorption. While ε and α can be equal under certain conditions/spectral matches, the direct factor in absorbed power is absorptivity (and geometry), so the statement as given is false.

Conclusion: The correct answer is False, which matches the provided answer.

When heat is radiated from a hot source, the amount of heat received by a nearby body depends on its emissivity.判断题

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