A human body with a typical temperature of 300K emits its maximum electromagnetic energy at 10 micrometers, which is in the infrared range and far from the visible wave spectrum. Why can we see each other?

Question

BlackTom AI · Accepted Answer

The question centers on why we can see each other despite human emission peaking in the infrared.
Option 1: 'Because human bodies reflect visible light and we are seeing each other because of the reflected visible light' correctly identifies the key mechanism. Even though a body’s thermal emission is mostly in the infrared, the visible spectrum light from ambient sources (sunlight, lamps, etc.) is reflected off surfaces, including our skin, and that reflected visible light is what our eyes detect. This reflects an interplay between emission and reflection and matches everyday experience of seeing people in lit environments.
Option 2: 'Because we all have superpower and can see in the infrared light' is incorrect. Humans do not rely on infrared vision for everyday sight; we use visible light to form images. This option introduces a fantastical concept not applicable to physics or biology.
Option 3: 'Even though human bodies mostly emit in the infrared range, we can see each other because we also emit a small amount in the visible range according to Planck’s law' contains a grain of truth in that thermal radiation spans a spectrum, including some visible components at extremely high temperatures, but at typical human body temperatures (around 300 K) the emitted visible power is negligible. The dominant reason we see others is reflection of external visible light, not self-emission. Relying on self-emission in the visible range would imply a noticeable brightness and color that we do not rely on in everyday scenes, making this explanation misleading.
Option 4: 'No answer text provided.' is not a usable explanation; it provides no reasoning and should not be selected as a valid answer.
In summary, the most accurate explanation highlights the role of reflected visible light from external sources in enabling us to see others, while recognizing that thermal emission into the infrared does not primarily drive visible perception in typical lighting conditions.

CLMT5001 Dynamics PRACTICE QUIZ: Week 2 Lecture 1

A human body with a typical temperature of 300K emits its maximum electromagnetic energy at 10 micrometers, which is in the infrared range and far from the visible wave spectrum. Why can we see each other?

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