Electromagnetic spectrum facts — wavelengths and the visible window Pick the correct combined statement about gamma-ray wavelengths, radio-wave wavelengths, and the visible band extent used in remote sensing.
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AThe wavelength of gamma rays is about 10^-10 m
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BThe wavelength of radio waves can be about 10^6 m
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CThe visible band occupies a small portion of the spectrum, roughly 0.4 μm to 0.7 μm
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DAll of these
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ENone of these
Answer
Correct Answer: All of these
Explanation
Introduction / Context:Remote sensing spans a wide portion of the electromagnetic spectrum (EMR). Understanding approximate wavelength scales helps relate sensor bands (visible, NIR, SWIR, TIR, microwave) to physical interactions including absorption, scattering, and emission.
Given Data / Assumptions:
- Order-of-magnitude wavelength values are acceptable.
- “Visible” refers to human-vision band ~0.4–0.7 μm.
- Long-wavelength radio can reach kilometre scales.
Concept / Approach:Gamma rays sit at the extreme short-wavelength end (on the order of 10^-12 to 10^-10 m). Radio waves span millimetres to kilometres; very long waves approach 10^6 m. The visible band is a narrow window between ultraviolet and near-infrared, about 0.4–0.7 μm.
Step-by-Step Reasoning:
1) Gamma: representative wavelength ~10^-10 m — extremely short.2) Radio: very long waves can be ~10^6 m (≈1000 km) in extreme cases.3) Visible: standard remote sensing window is ~0.4–0.7 μm.Verification / Alternative check:Textbook EMR charts show the visible as a tiny slice, framed by UV below 0.4 μm and NIR above 0.7 μm; radio spans many orders of magnitude.
Why Other Options Are Wrong:
- Each single statement is correct; selecting only one omits the others.
- None of these: incorrect because all given statements hold.
Common Pitfalls:Confusing micrometres (μm) with millimetres (mm); mixing “typical value” with “only value” — spectrum bands cover ranges.
Final Answer:All of these