Simple equipment for teaching internal photoelectric effect

In this paper, an educational tool is proposed to show the internal photoelectric effect in a simple and clear way for Undergraduate Physics courses or High Schools. Experimental evidence of the photoelectric effect is particularly important in the didactic experience. This effect is fundamental to introduce students to the world of quantum mechanics, and to the concept of quantized energy. However, it often requires uneconomical and not easy to use equipment. For this reason, here we describe the realization of a simple and low-cost system based on the LED to LED structure; LEDs can in fact act as light sources, but also as photodetectors, being sensitive to wavelengths equal to or shorter than the predominant wavelength they emit. Through the lightning of LEDs of different colors, we thus show that the verification of the photoelectric effect becomes easy.