Announcements

22 posted

• 8/24/2026, 5:09:42 PM

  LATEST
  OPhO 2026 is over. Thank you to everyone who competed! Grading of the long answer and simulation problems is underway. Results will be posted here and emailed to you as soon as they are final.

• 8/23/2026, 9:01:40 PM

  Problem 15 (Aberration): The graph is intensity as a function of distance away from optical axis on the focal plane--in case it's not clear the focal plane is defined parallel to the flat surface of the lens.

• 8/23/2026, 6:15:46 AM

  Problem 23 (Spinny Spin Spin): You may take a positive value for $B_1$.

• 8/23/2026, 3:04:45 AM

  Problem 22 (Einstein Ring): We forgot to include the image in the problem statement (but it was always in the PDF). It is now included.

• 8/23/2026, 3:01:33 AM

  Open #9: In the problem statement, the term 'normal' refers to the normal of the length side of the slab. Please understand that the beam is trapped. The separation between centers is measured perpendicular to the beam's direction of propagation.

• 8/23/2026, 2:38:26 AM

  Open #6: Do not assume what is not given in the diagram. There are no direct resistor connections between nodes A and B, nor between the nodes C and D.

• 8/22/2026, 10:39:50 AM

  For individuals: Team rosters can now be created or joined at any time during the contest, including right now. If you or a teammate weren't on a team yet, create one or accept a pending invite from the onboarding page. ONCE you've submitted an answer under a team, you're locked to that team for the rest of the contest. No switching after that, so make sure you're on the right team before your first submission.

• 8/22/2026, 2:25:54 AM

  Problem 16 (Bee Greed): Error bound increased and better image given.

• 8/21/2026, 10:55:09 PM

  Problem 10 (Countless Collisions): 1. The only collisions that may be neglected are collisions between the small balls and the dispenser; treat the balls as (unphysically) freely passing through the dispenser. 2. The $-$ in $-v_0$ is a negative sign, not a hyphen.

• 8/21/2026, 10:47:22 PM

  Problem 14 (Pursuit of Happiness?): $d$ is measured in the lab frame.

• 8/21/2026, 9:52:02 PM

  Problem 16 (Bee Greed): Problem statement has been modified and all attempts have been refunded.

• 8/21/2026, 12:58:37 PM

  Problem 23 (Spinny Spin Spin): You can run the simulation as many times as you wish.

• 8/21/2026, 9:43:28 AM

  Problem 19 (Whiplash): Problem statement has been reworded to be clearer.

• 8/21/2026, 8:53:06 AM

  Problem 3 (Kugel Fountain): the problem statement has been reworded to be clearer. In particular, note that the flat side of the puck is resting on the base of the fountain, not the curved side.

• 8/21/2026, 7:52:14 AM

  Problem 23 (Spinny Spin Spin): 1. There is no uncertainty in the selected time. 2. "The environment" is shorthand for thermal noise--$B_0$, $B_1$ and $b$ are not noise and so are not part of the environment and the spins still interact with them afterwards.

• 8/21/2026, 7:22:03 AM

  Problem 23 (Spinny Spin Spin): You may treat the problem as if there were two sensors, one for the total magnetic moment around the x-axis which reads out to $M_x$ and one for the total magnetic moment around the y-axis which reads out to $M_y$. (In a real setup this can be done with one sensor, but that is besides the point) And just to clarify, $M_x$ and $M_y$ are components of the total magnetic moment of the system, which is obtained by a vector sum over all of the magnetic moments of the particles and then divided through by ${\mu }_B$. (Just realised that this would've been very easy to confuse with magnetisation, apologies!)

• 8/21/2026, 4:45:32 AM

  Problem 8 (Fabric of Reality): improved wording. Problem should be much easier to understand now.

• 8/21/2026, 4:45:18 AM

  Open#6 — Accessibility Information for Colour-Blind Participants The following colour assignments apply to the resistors shown in the circuit diagrams: Circuit 1 - Resistors oriented at 60° to the horizontal: green - Resistors oriented at −60° to the horizontal: blue - Resistors oriented at 0° to the horizontal: yellow Circuit 2 - Resistors oriented at 30° to the horizontal: red - Resistors oriented at 90° to the horizontal: grey - Resistors oriented at −30° to the horizontal: magenta

• 8/21/2026, 12:03:30 AM

  Reminder: as part of our anti-cheating measures, you will need to submit a solution to every problem. The short-answer solutions will not be graded, and will only be looked at when investigating competition dishonesty.

• 8/20/2026, 3:09:11 PM

  See the OPhO 2026 Rules

• 7/15/2026, 8:00:12 PM

  TEAM RULES - Up to 3 people per team, including the leader. A pending invite holds a seat until it's accepted or revoked. - Invites aren't emailed. Tell your teammate yourself; they join by signing in with the exact address you invited, then accepting. - Only the leader can invite teammates, revoke invites, or rename the team. - You can hold invites from several teams but can only join one. Accepting one withdraws the rest. - Nobody can join, leave, or switch teams while a round is live. - If the leader leaves, leadership passes to the longest-standing teammate. If they're the only member, the team is deleted.

• 6/24/2026, 12:27:53 AM

  OPhO 2026!!