Question

The maximum spectral radiant exitance from Earth features occurs at a wavelength of:

• A. \(\text{about } \) 0.7mu m
• B. \(\text{about } \) 1.7 mu m
• C. \(\text{about } \) 9.7 mu m
• D. \(\text{about } \) 19.7 mu m

Hint:

The Earth's thermal radiation peaks in the infrared region (9-10 µm), which is why thermal imaging and remote sensing rely on this wavelength range.

Answer 1

The Correct Option is C

Step 1: Understanding the concept of spectral radiant exitance. The Earth's surface emits thermal radiation primarily in the infrared region due to its temperature, which follows Planck’s Law and Wien’s Displacement Law. 

Step 2: Applying Wien's Displacement Law. Wien’s Law states: \[ \lambda_{\max}  = \frac{2898} {T} \] For Earth's average surface temperature (~288 K): \[ \lambda_{\max}  = \frac{2898} {288}  \approx 10 \ \mu m. \] 

Step 3: Selecting the correct option. The peak emission for Earth’s features occurs near 9.7 to 10 µm, which is in the thermal infrared range.