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MCQ practice · SSC Physics Board questions · Chapter 8: Reflection of Light

Mymensingh Board 2021

Which of the following is the wavelength of visible light?

Think it through first, then pick an option.

  1. a 300 ηm − 700 ηm
  2. b 400 ηm − 700 ηm
  3. c 300 µm − 700 µm
  4. d 400 µm − 700 µm
Answer and explanation

Correct answer: b 400 ηm − 700 ηm

Here ηm stands for nanometre (nm); 400 to 700 nm is the visible range.

Why the other options are wrong

  • a 300 ηm − 700 ηm: This is not the answer: 300 nm lies in the ultraviolet, not the visible range. The visible range is 400 nm to 700 nm.
  • c 300 µm − 700 µm: This is not the answer: 1 µm = 1000 nm, so 300 to 700 µm is a far longer wavelength, past infrared and toward the microwave.
  • d 400 µm − 700 µm: This is not the answer: 1 µm = 1000 nm, so 400 to 700 µm is a thousand times the visible range; the eye does not see it.

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