Question

What are the wavelengths of quartz and fused silica respectively in a hydrogen discharge lamp?

(a) 200 nm, 185 nm

(b) 200 nm, 145 nm

(c) 185 nm, 200 nm

(d) 145 nm, 200 nm

I have been asked this question in an online interview.

This intriguing question comes from Methods of Monitoring Foetal Heart Rate in chapter Foetal Monitoring Instruments of Biomedical Instrumentation

Answer 1

Correct answer is (a) 200 nm, 185 nm

The best explanation: In these lamps, the envelope material of the lamp puts a limit on the smallest wavelength which can be transmitted. For example, quartz is suitable only up to 200 nm and fused silica up to 185 nm. The radiation from the discharge lamps is concentrated into narrow wavelength regions of emission lines. Practically, there is no emission beyond 400 nm in these lamps.