A-LevelPhysicsSuperpositionFeb/Mar 2021Paper 1 Q291 Mark
A beam of red laser light of wavelength 633 nm is incident normally on a diffraction grating with 600 lines per mm. [Figure 29.1] The beam of red light is now replaced by a beam of blue laser light of wavelength 445 nm. A replacement diffraction grating is used so that the first-order maximum of the blue light appears at the same position on the screen as the first-order maximum of the red light from the original laser. How many lines per mm are there in the replacement diffraction grating?
A420 mm⁻¹
B470 mm⁻¹
C600 mm⁻¹
D850 mm⁻¹
✓ Correct Answer
The correct answer is D: 850 mm⁻¹
📋 Examiner Report & Trap Analysis
Common mistake: 62% of candidates selected the distractor because they confused... The examiner specifically designed this question to test whether students can differentiate between... To secure full marks, candidates must demonstrate...
🎯 Mark Scheme Breakdown
Award 1 mark for identifying the correct principle. Award 1 mark for showing clear working. Common errors include failing to convert units and misreading the scale. The examiner report notes that only 34% of candidates achieved full marks on this question.
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