A physicist is asked to design an infrared system to detect human beings (at a normal temperature of 310 K) in darkness. What would the wavelength of peak sensitivity of the equipment need to be?
A) 9.35 $\mu$m
B) 0.935 $\mu$m
C) 0.00094 $\mu$m
D) 90 $\mu$m

Question

Quizplus · Accepted Answer

The peak wavelength ($\lambda_{max}$) at which a black body radiates can be found using Wien's displacement law, $\lambda_{max} = \frac{b}{T}$, where $b$ is Wien's displacement constant ($2.898 \times 10^{-3} m \cdot K$), and $T$ is the temperature in Kelvin. For a human body at 310 K, $\lambda_{max} = \frac{2.898 \times 10^{-3}}{310} \approx 9.35 \times 10^{-6} m$ or 9.35 $\mu m$, which falls within the infrared range, making choice A correct.

A Physicist Is Asked to Design an Infrared System to Detect