A-LevelPhysicsSuperposition9702/12 · Oct/Nov 2015 · Q291 Mark
White light consists of many wavelengths. The wavelength of red light R is approximately twice the wavelength of violet light V. When white light is incident normally on a diffraction grating, several spectra can be formed. Which diagram shows the possible distributions of light in the first order and the second order spectra?
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
ADiagram A showing two spectra, the first order with violet and red, and the second order also with violet and red. The red end of the first order spectrum appears to align with the violet end of the second order spectrum, with the second order spectrum being wider.
BDiagram B showing two spectra, first and second order. The second order spectrum is entirely separate from and at greater angles than the first order spectrum.
CDiagram C showing two spectra, the first order with violet and red, and the second order also with violet and red. The red end of the first order spectrum appears to align with the violet end of the second order spectrum, with the second order spectrum being wider.
DDiagram D showing two spectra, first and second order. The red end of the first order spectrum starts at a smaller angle than the violet end of the second order spectrum, and they are distinct.
✓ Correct answer
C: Diagram C showing two spectra, the first order with violet and red, and the second order also with violet and red. The red end of the first order spectrum appears to align with the violet end of the second order spectrum, with the second order spectrum being wider.
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