What can radiate electromagnetic energy?

Question

BlackTom AI · Accepted Answer

In addressing the question of what can radiate electromagnetic energy, I will evaluate each statement for accuracy and underlying physics.
Option 1: 'All objects can radiate electromagnetic energy.' This is too broad. While many objects do emit some EM radiation, the amount and spectrum depend on temperature. Objects at absolute zero do not emit thermal radiation, so the blanket claim that all objects radiate is incorrect.
Option 2: 'All objects above zero Kelvin can radiate electromagnetic energy.' This aligns with the concept of thermal radiation: any object with a nonzero temperature emits EM radiation across a spectrum determined by its temperature (described by Planck's law). Even at very low temperatures, there is some emission, so the statement is accurate in thermodynamic terms.
Option 3: 'All objects above zero Celsius can radiate electromagnetic energy.' Zero Celsius corresponds to 273.15 K. While many objects above this temperature radiate, this statement excludes objects that are between 0 C and 273.15 K or just above 0 C; more importantly, the fundamental threshold for radiation is Kelvin temperature, not Celsius, so tying it to Celsius creates an unnecessary limitation.
Option 4: 'All objects above zero Fahrenheit can radiate electromagnetic energy.' Zero Fahrenheit is about -17.78 C, which is a temperature well below the typical range where we consider practical thermal emission onset. Like the Celsius variant, this ties radiation to an arbitrary Fahrenheit threshold and is not the correct physics linkage for thermal radiation, which is governed by Kelvin temperature.
Overall, the most accurate description among the choices is the one that uses the absolute temperature scale (Kelvin) to indicate the presence of thermal radiation, since emission occurs for any T > 0 K and increases with temperature. The other options introduce incorrect thresholds or broad generalizations that fail to capture the temperature-dependent nature of electromagnetic radiation from objects.

GEOM30009_2025_SM1 6.3 - Assessment Task 3: In-class online quiz

What can radiate electromagnetic energy?

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