He stopped sleeping. The problems consumed him. On day ten, he reached Problem 999: "A plane electromagnetic wave in vacuum has an electric field given by E = E₀ cos(kz - ωt) x̂. Find the magnetic field." He solved it in his head before the animation confirmed it. He grinned.
He was hooked. Problem 87 on Biot–Savart law made a current loop twist in 3D. Problem 304 on Faraday's Law let him slide a magnet through a coil and watch the galvanometer needle swing. The PDF was a silent tutor, a patient magician. By Problem 500, he could feel divergence as water flowing from a source. By Problem 750, curl was no longer an abstraction but the twist of a tiny paddle wheel in a vector field.
One night, buried in the library's sub-basement, he found a forgotten server. On it was a single file: 1000_Solved_Problems_Electromagnetism_FINAL.pdf .
Then he clicked .