Which law governs total emitted radiation from a blackbody in thermography?
A) Fourier’s Law
B) Newton’s Law
C) Stefan–Boltzmann Law
D) Ohm’s Law
Answer: C) Stefan–Boltzmann Law
This question is asking about the fundamental physical law that explains how much energy a perfect emitter (called a blackbody) radiates, which is extremely important in thermography because infrared cameras measure radiation, not temperature directly. When a body emits thermal radiation, the amount of energy it gives off depends strongly on its temperature, and this relationship is not linear but very steep. That is exactly what the Stefan–Boltzmann Law describes.
According to the Stefan–Boltzmann Law, the total radiant energy emitted per unit surface area of a blackbody is proportional to the fourth power of its absolute temperature. In simple terms, if the temperature of an object increases slightly, the radiation it emits increases very rapidly. For example, if the temperature doubles (in Kelvin), the emitted radiation increases by 16 times (because 2⁴ = 16). This is why hot objects glow intensely in infrared images and why thermography is very sensitive to temperature differences.
In thermography, this law is critical because infrared cameras detect emitted radiation and then convert that radiation into a temperature reading. The camera assumes a relationship based on this law (along with emissivity corrections) to calculate accurate temperatures. If this law did not exist or was not understood, thermographic measurement would not be possible in a scientific or reliable way.
Now, looking at the other options helps reinforce why they are incorrect. Fourier’s Law is related to heat conduction, meaning how heat flows through a material due to temperature gradients, not how it is emitted as radiation. Newton’s Law (often referring to Newton’s Law of Cooling) describes how an object loses heat to its surroundings, mainly through convection, not radiation emission in this context. Ohm’s Law is completely unrelated, as it deals with electrical circuits and the relationship between voltage, current, and resistance.
So, the correct concept behind this question is the Stefan–Boltzmann Law because it directly governs the total emitted radiation from a blackbody, forming the theoretical backbone of infrared thermography.
