Question

4) Which of the statements about an arbitrarily shaped conductor in electrostatic equilibrium is true? Choose d if more than one is true. a) the electric field strength at some point just outside the conductor is s/e0 where s is the local surface charge density at that point b) the electric field E at the surface is directed tangent (parallel) to the conductor’s surface c) the electric field E is continuous as you move from the inside of the conductor to the outside; this means that E varies smoothly with no abrupt change in E d) more than one of the above is true

6) Consider a solid conducting sphere of radius R and charge Q in electrostatic equilibrium. Take the potential at infinity to be zero. A true statement is a) the potential difference between a point at infinity and a point within the sphere is kQ/R b) the potential difference between any two points on the surface of the sphere is kQ/R c) the electric potential outside the sphere falls off as 1/r2 d) exactly two of the above is true e) none of the above is true

8) Consider two spherical conductors of radii R1 and R2 separated by a distance much greater than their radii. A conducting wire connects the spheres and electrostatic equilibrium is achieved. Each sphere then has uniform charge distribution and charge Q1 and Q2 respectively. Choose one of the following as true: a) Q1/ Q2 = R1 / R2 b) E1 / E 2 = (R2 / R1) 2 at the surface of the spheres c) Q1/ Q2 = R2 / R1 d) More than one of a-c is true (answer if 2 or 3 of a-c are true) e) None of the above is true (answer if none of a-c is true)

15) Consider a parallel plate capacitor with capacitance C. If the area of each plate is doubled, and the distance between the plates is doubled, the capacitance is now a) C/4 b) C/2 c) C d) 2C e) none of the above is true

20) A cylindrical capacitor of length L has central conductor of radius R1 and outer shell of radius R2 so the gap between them is R2-R1. Assume the space between the two surfaces is air. In the limit R2-R1<< R1, which of the choices below is the best approximate formula for the capacitance. a) zero b) e02pR1L / (R2-R1) c) e0pR1 2 / (R2-R1) d) none of the above is true

21) A parallel plate capacitor with some charge on it and isolated (not electrically connected to anything) stores energy Ui. If the distance between its plates is now doubled (for example by some external force pulling or pushing the plates apart), the new stored energy is: a) 2 Ui b) 4 Ui c) Ui/2 d) Ui/4 e) none of the above is true

Answer 1