He pulled out the 2023 Paper 2. Question 12: A nucleus of uranium-238 decays by alpha emission. The alpha particle has kinetic energy 4.2 MeV. Calculate the speed of the recoil nucleus. He’d done it correctly—conservation of momentum—but then forgotten to convert MeV to joules. A common trap. The examiner’s report even had a sad face emoji in the margin of one candidate’s script: “Many lost the final mark here.” Daniel had made the same mistake. Twice, across different years.
He flipped to 2021 Paper 1, multiple choice. Question 17: A particle moves in a circle with constant angular speed. Which graph shows the variation of its acceleration with time? The obvious answer—a sine wave—was wrong. Centripetal acceleration for uniform circular motion is constant in magnitude, only direction changes. The graph should be a straight line. He’d chosen the sine wave in his first attempt. The mark scheme said: B (straight line). Common distractor: C (sinusoidal). He drew a star next to it. past papers a level physics
Walking out, Priya grabbed his arm. “Question 4? The one with the diffraction grating and the two wavelengths? Did you use nλ = d sinθ or the small angle approximation?” He pulled out the 2023 Paper 2
He began to notice patterns. The same magnetic flux linkage graph appeared in 2019, 2021, and 2024—only the numbers changed. The same six-mark essay on the photoelectric effect and why it proved light was particle-like: state threshold frequency, mention one-to-one photon-electron interaction, explain why wave theory fails (no time lag, dependence on frequency not intensity). He wrote a model answer, memorized it, then realized the 2023 paper asked the opposite: Explain how electron diffraction proves wave-particle duality. Two sides of the same coin. Calculate the speed of the recoil nucleus