Question

Which of the following wavelength (nm) correspond to visible range of humans ?
A. 20 nm
B. 200 nm
C. 400 nm
D. 600 nm
E. 900 nm

• A. A and B Only
• B. C and D Only
• C. D and E Only
• D. B, C and D Only

Hint:

Always memorize the visible spectrum as strictly the 400-700 nm range. Anything lower (like 200 nm) is UV (causes sunburns, invisible), and anything higher (like 900 nm) is IR (heat signatures, invisible).

Answer 1

The Correct Option is B

Step 1: Concept:
This question requires identifying the specific portion of the broad electromagnetic (EM) spectrum that is perceivable by the photoreceptors in the human eye, measured in units of nanometers (nm).

Step 2: Step-by-step Explanation:

• The human visual system is biologically adapted to detect electromagnetic radiation only within a very specific, narrow band known as the visible light spectrum.

• This visible spectrum generally ranges from approximately 400 nanometers (nm) at the violet end to about 700 nanometers (nm) at the red end.

• Let us evaluate the given wavelength options against this standard biological range:
- A. 20 nm: This very short wavelength falls in the extreme Ultraviolet (UV) or soft X-ray region, which is completely invisible to human eyes and is highly ionizing.
- B. 200 nm: This falls in the UV-C region (used for germicidal irradiation), which is also invisible and harmful to humans.
- C. 400 nm: This sits exactly at the lower boundary of the visible spectrum, corresponding to violet or deep blue light.
- D. 600 nm: This wavelength sits comfortably in the middle-upper section of the visible spectrum, corresponding to orange or reddish light.
- E. 900 nm: This long wavelength falls in the near-Infrared (IR) region. While we might feel it as heat, our eyes cannot see it.

• Therefore, only 400 nm and 600 nm fall within the human visible range.

Step 3: Final Answer:
Options C and D are correct, matching choice (B).