The first experiment, which we'll talk about in great detail in another lecture was called a photoelectric experiment or simply the Photo Electric effect. And this experiment was conducted by Einstein. And what Einstein showed was that light, an electromagnetic phenomenon, had both particle like properties as well as wavelike properties. In other words, light has the following property called wave particle duality. And what this property shows or tells us is that whenever it's convenient, light can act as a wave. And whenever it's convenient, light will act as a particle.