Chemical Interactions - General Physics - Solved Past Paper, Exams of Physics

Download Chemical Interactions - General Physics - Solved Past Paper and more Exams Physics in PDF only on Docsity! 1. (25 pts) a) Does the choice of charge signs have any bearing on physical or chemical interactions? In other words, if the proton had been called “negative” and the electron “positive,” would life be any different? What we call the charges is immaterial to how they interact. It doesn’t matter whether we call a proton “+” or “-”, or even “vanilla” with the electron called “strawberry.” They way they act in nature will remain exactly the same. (In fact, some sub-nuclear interactions are called “flavors.”) b) Explain why any net charge on a conductor in electrostatic equilibrium must reside on the surface of the conductor. This effect is based on two things: (a) charge can move in a conductor and (b) charges of like sign repel. If you inject a net charge (all of the same sign) into a conductor, the pieces will repel. Since it is in a conductor, the pieces of charge can (and do) move away from eachother, stopped only when reaching the surface of the conductor. Thus the net charge must be at the surface. c) Explain why the electric field immediately outside a conductor must be perpendicular to the conduc- tor surface, again assuming electrostatic equilibrium conditions. The key here is that we are discussing electrostatic conditions. If the electric field were not perpen- dicular to the surface of the conductor, a force parallel to the surface of the condutor would be exerted on charges at the surface, which would then start to move along the surface. Since charges do not move (once quickly reaching equilibrium) under electrostatic conditions, this cannot be the case. Thus the only orientation of a non-zero electric field at the surface of the conductor is perpendicular to the surface. d) If more electric field lines are leaving a Gaussian Surface than entering, what can you conclude about the charge enclosed by the surface? The (net) charge enclosed by the surface is positive. e) (5 pts) Two equal point charges are separated by some distance d. At what point(s) would a third test charge experience no net force? At the exact center between the charges the electric field would be zero. However, the electric field is also zero very far away from the charges.