2026 · Paper 2 · Physics

Question 3

The printed question, the official key, and each model’s JSON answer plus the reasoning it wrote.

PhysicsPaper 2Single correct

Q03

Official B

JEE Advanced 2026 Paper 2 Physics question 3

Model answers

Claude Fable 5.1

Anthropic

Correct3 / 3

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

Correct3 / 3

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

Correct3 / 3

B

GPT 5.5 reasoning

No written reasoning was returned for this item.

Claude Sonnet 5

Anthropic

Correct3 / 3

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.