Answer
Calibration of the Violet Spectral Line on a Spectroscope
When calibrating a spectroscope, specific colors of visible light correspond to well-known wavelengths:
- Violet: ~380–450 nm
- Blue: ~450–495 nm
- Green: ~495–570 nm
- Yellow: ~570–590 nm
- Red: ~620–750 nm
Since the violet region of the visible spectrum begins around 400 nm, that is the most appropriate calibration point for the violet spectral line.
✔ 400 nm — Correct
This is the beginning of the visible spectrum and matches the lower end of violet light. The violet line should be calibrated here.
✘ 450 nm — Incorrect
This falls within the blue-violet transition zone, not true violet. It’s too far along the spectrum.
✘ 550 nm — Incorrect
This lies in the green part of the spectrum — much higher in wavelength than violet light.
✘ 700 nm — Incorrect
This is deep in the red region of the spectrum — far from the violet end.
Final Answer: 400 nm is the correct point to calibrate the violet spectral line on a spectroscope.