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Date May 2011 Marks available 4 Reference code 11M.3.SL.TZ1.21
Level Standard level Paper Paper 3 Time zone Time zone 1
Command term Determine Question number 21 Adapted from N/A

Question

This question is about using a diffraction grating to view the emission spectrum of sodium.

Light from a sodium discharge tube is incident normally upon a diffraction grating having 8.00×105 lines per metre. The spectrum contains a double yellow line of wavelengths 589 nm and 590 nm.

Determine the angular separation of the two lines when viewed in the second order spectrum.

[4]
a.

State why it is more difficult to observe the double yellow line when viewed in the first order spectrum.

[1]
b.

Markscheme

\(d = \frac{1}{{8.00 \times {{10}^5}}} = 1.25 \times {10^{ - 6}}{\rm{m}}\);
\(d\sin \theta  = n\lambda  \Rightarrow \theta {\sin ^{ - 1}}\left[ {\frac{{n\lambda }}{d}} \right]\);
\({\sin ^{ - 1}}\left[ {\frac{{2 \times 589 \times {{10}^{ - 9}}}}{{1.25 \times {{10}^{ - 6}}}}} \right] = {\rm{ }}70.5^\circ {\rm{ }},{\sin ^{ - 1}}\left[ {\frac{{2 \times 590 \times {{10}^{ - 9}}}}{{1.25 \times {{10}^{ - 6}}}}} \right] = 70.7^\circ \);
70.7°−70.5°=0.2°;

a.

the lines are closer together / not clearly separate in the first order spectrum;

b.

Examiners report

[N/A]
a.
[N/A]
b.

Syllabus sections

Additional higher level (AHL) » Topic 9: Wave phenomena » 9.3 – Interference
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