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Question 18N.2.HL.TZ0.b.i

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Date November 2018 Marks available [Maximum mark: 2] Reference code 18N.2.HL.TZ0.b.i
Level HL Paper 2 Time zone TZ0
Command term Show that Question number b.i Adapted from N/A
b.i.
[Maximum mark: 2]
18N.2.HL.TZ0.b.i

A low-pressure hydrogen discharge lamp contains a small amount of deuterium gas in addition to the hydrogen gas. The deuterium spectrum contains a red line with a wavelength very close to that of the hydrogen red line. The wavelengths for the principal lines in the visible spectra of deuterium and hydrogen are given in the table.

Light from the discharge lamp is normally incident on a diffraction grating.

The light illuminates a width of 3.5 mm of the grating. The deuterium and hydrogen red lines can just be resolved in the second-order spectrum of the diffraction grating. Show that the grating spacing of the diffraction grating is about 2 × 10–6 m.

[2]

Markscheme

λ 2 Δ λ = 656.20 0.181 × 2 = 1813 «lines» ✔

so spacing is  3.5 × 10 − 3 1813  «= 1.9 × 10−6 m» ✔

 

Allow use of either wavelength or the mean value

Must see at least 2 SF for a bald correct answer

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