Hi, This is my virgin post. This forum has been a great source of information for the past one year. I am a high school teacher from Singapore. In the study of electrostatics (more specifically induction), we often encounter the scenario below: Two insulated metal spheres touching each other. A negatively charged rod is brought near to the left hand side of the system of spheres. A common question will be to label the distribution of induced charges, which in this case the solution will be: the positive charges (attracted) will be on the left hand side of the system, while the negative charges (repelled) will be on the right hand side. Explanation: electrons are repelled to the right hand side of the system. We can assume that the "loose valence electrons" on the left sphere can cross over to the right sphere (am i right to assume this?:shy:). My main question: Let's say if i modify the question by saying that a positively charged rod is brought near to the left hand side of the system of spheres. Is it right to say that the repelled positive charges move from the left sphere to the right sphere, instead of always saying that the mobile charge carriers are electrons (in this case moving from right to left under the influence of attraction)? My current understanding is no. Atoms in a metal solid are tightly held together. We can extend this strong rigid of particles to charged atoms (aka positive charges) as well. Hence, for metallic conductors, the only mobile charge carriers are electrons. I would like to seek the opinons of fellow forummers here. Comments and feedback are much appreciated.