Thermal radiation takes place only at a certain temperature for every body.

Question

BlackTom AI · Accepted Answer

All objects with a temperature above absolute zero emit thermal (electromagnetic) radiation. Relevant concepts: Planck’s law describes the spectral distribution of thermal radiation at any temperature T, and the Stefan–Boltzmann law gives the total radiative power per unit area: j = ε σ T^4, where σ ≈ 5.670×10^−8 W·m^−2·K^−4 and ε (emissivity) is between 0 and 1 for real materials.

Step-by-step reasoning:
1. According to Planck’s law, a body at temperature T emits photons over a continuous range of wavelengths; the peak wavelength shifts with temperature (Wien’s displacement law), but emission is nonzero for any T > 0 K.
2. The Stefan–Boltzmann law (j = ε σ T^4) shows total radiative flux depends on T^4. For a perfect blackbody (ε = 1) at room temperature (T = 300 K), j = σ T^4 = 5.67×10^−8 × (300)^4.
3. Calculation: (300)^4 = 8.1×10^9, so j = 5.67×10^−8 × 8.1×10^9 = 5.67×8.1×10^(9−8) ≈ 45.927×10^1 ≈ 459 W/m^2. This is a clearly nonzero emission at ordinary temperature, confirming radiation is not restricted to a single “certain temperature.”
4. Only at absolute zero (T = 0 K) does the ideal blackbody emission go to zero. Real bodies have emissivity ε < 1, so their emitted power is εσT^4, still nonzero for T > 0 K unless ε = 0 (an ideal, non-emitting perfect reflector, which is not common in reality).

Why the correct answer is correct: The statement claims thermal radiation occurs “only at a certain temperature” for every body; this contradicts Planck’s and Stefan–Boltzmann laws and experimental evidence showing emission at all T > 0 K. Therefore the statement is false.

Why the other option is incorrect: “True” would imply radiation occurs only at one specific temperature (or only at some threshold), which is inconsistent with the continuous T dependence in j = εσT^4 and with observed emission at everyday temperatures.

Conclusion: The correct response is False, matching the provided answer.

Thermal radiation takes place only at a certain temperature for every body.判断题

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