2026 · Paper 2 · Physics
Question 3
The printed question, the official key, and each model’s JSON answer plus the reasoning it wrote.
Q03
Official B

Model answers
Claude Fable 5.1
Anthropic
B
Claude Fable 5.1 reasoning
n(λ) = αλ + β/λ². Minimize: dn/dλ = α − 2β/λ³ = 0 → λ³ = 2β/α = 2(0.096)/3 = 0.064 → λ = 0.4 μm. n = 3(0.4) + 0.096/0.16 = 1.2 + 0.6 = 1.8. D_m = (n−1)A = 0.8 × 6° = 4.8°.
GPT 6 Astra
OpenAI
B
GPT 6 Astra reasoning
**Calculating dimensions and JSON** I need to solve this straightforward problem. I have n = 3λ + .096/λ² to minimize. It leads me to λ³ = .192/3, which gives me λ = .064 or .4 micron. After that, I find n1 as 1.2 + .6 = 1.8. Also, I have D = .8 * 6, resulting in 4.8 B. My next goal is to finalize the JSON for this, ensuring it meets the user's expectations, which seem to be somewhat ambiguous. Let’s get that JSON ready!
GPT 5.5
OpenAI
B
GPT 5.5 reasoning
No written reasoning was returned for this item.
Claude Sonnet 5
Anthropic
B
Claude Sonnet 5 reasoning
Minimizing n(λ) by setting the derivative to zero gives λ³=2β/α, and plugging in α=3 and β=0.096 yields λ=0.4 μm, so n at this wavelength equals 1.8. Now I'm computing the prism deviation using D=(n-1)*A.