Final answer:
Young performed his double-slit experiment to demonstrate the wave behavior of light. By passing light through two closely spaced slits, he created two coherent light sources that interfered constructively or destructively, resulting in a pattern of bright and dark fringes on a screen.
Step-by-step explanation:
Young did his famous double-slit experiment to demonstrate the wave behavior of light. He passed light from a single source (the Sun) through a pair of closely spaced slits to create two coherent light sources. These two slits provided two coherent light sources that interfere constructively or destructively. The interference created a pattern of bright and dark fringes on a screen, showing the wave-like nature of light.