Solution errata are in dropdowns so you don’t have to see it.

I’ve provided very rough cutoffs for 2024 and 2025. Don’t take them too seriously; they’re just there for reference and I don’t actually know the real cutoffs as scores are not released.

2025

• cutoff

I have not checked this year very thoroughly as they do not return your working and I do not intend on going through this again. There was also an error in P9 and a few typos around but they have been fixed in the latest version.

Note: P1 is probably inspired by the 2018 All-Russian Olympiad and P4B is copied from the 2019 All-Russian Olympiad. P6B seems loosely inspired by APhO 2017 T1.

• P1: Part (a) is phrased quite badly; just don’t do it. Assign the one mark to P7(c) or something.

• P7A: Ignore the light ray reflecting off the top of the lens.

  In reality lenses are usually thick enough that this isn’t an issue as the maxima would probably be blurred by imperfections, but because the question specifically states that it is a “thin lens” interference, they are pretty much shooting themselves in the foot.

• P7B: Part (c) is pointless and has loads of issues. Skip part (c) and do part (d) directly. In part (d), you have to assume that $\delta \lambda/\lambda \ll \lambda r /d^2$, and find $I(\theta,t)$ in the limit of $\theta \ll 1$.

• P7B

2024

• cutoff

i was too lazy to check P2 and P9’s answer because P2’s answer was too big and i don’t feel like doing P9.

Note: multiple questions have minor deviations between the answer key and the question. It seems like the question/answer may have been modified last minute.

Note: P8 is copied from the 2016 All-Russian Olympiad.

• P1: The radius of the ring is $r$, which you may use this in your answer. Also, replace all mentions of “velocity” with “speed”. For part b, you are supposed to eliminate $\theta$.
• P2: To be clear, they are asking for the speed of the rod as a function of time. This question should be worth a lot more than 5 points but whatever, mark balance is wack.
• P3: $v$ should be bolded ($\mathbf v$) since it is a vector.
• P5: For (a), you are supposed to write $x(t)=x_0 \cos(\omega t-\phi)$, and find the parameters of that equation. For (f), assume that $v \ll c$ at first, and the low velocity limit is an even stronger limit where $kv \ll |\Delta|$.