Conductors and insulators Look at Figures (a)-(d). Each shows a complete electric circuit. Then why is it that the bulb glows only in circuits (b) and (d)? It is because not all materials allow electric current to pass through them.A material that allows electric current to pass through it is called a conductor of electricity like the key and the safety pin [Figs. (b) … [Read more...] about What is an Insulator and a Conductor