This document provides details and solutions to three theoretical and two experimental problems from the XV International Physics Olympiad held in 1984. Theoretical Problem 1 involves calculating refractive indices based on a diagram of a plane-parallel transparent plate with a varying refractive index. Part b) explains total reflection in a warm air layer, and part c) computes the air temperature close to the ground based on given refractive indices. Theoretical Problem 2 models the oscillation period of water in rectangular containers based on experimental data, deriving a formula and comparing it to measurements. Theoretical Problem 3 involves constructing an electronic frequency filter from given components to meet voltage ratio and phase specifications. Possible configurations are provided. Experimental Problem 1