Why do thin french fries cook faster than thick fries?

Surface area to volume ratio.

- When the fry is exposed to hot oil during the frying process, its outer later begins to cook and form a crust.

- Thin fries contain proportionally more surface area in contact with this hot oil than thick fries because they have larger surface to volume ratio of fries, they heat and cook to the ideal crispness very quickly compared to thicker ones.