Question
General Physics II
Problem 1 The earth (a conductor) has a net electric charge. The resulting electric field near the surface has an average value of about 150 N/C directed toward the center of the earth (a) What is the corresponding surface charge density? (b) What is the total surface charge of the earth? Problem 2 In a hydrogen atom, the electron and proton are bound at a distance of about 0.53 Å. (a) Estimate the potential energy of the system in eV, taking the zero of the potential energy at infinite separation of the electron from proton in the orbit is half the magnitude of the potential energy obtained in (a)? 1.06 A separation (b) What is the minimum work required to free the electron, given that its kinetic energy (c) What are the answers to (a) and (b) above if the zero of potential energy is taken at Problem 3 Two charges 3 × 10-8 C and 2 × 10-8 C are located 15 cm apart. At what point(s) on the line joining the two charges is the electric potential zero? Take the potential at infinity to be zero Problem 4 Figures (a) and (b) show the field lines of a positive and a negative point charge respectively (a) Give the sign of the potential difference p-Vo; VB - VA. Explain (b) Give the sign of the potential energy difference of a small negative charge betweern (c) Give the sign of the work done by the field in moving a small positive charge from Q (d) Give the sign of the work done by the external agency in moving a small negative (e) Does the kinetic energy of a small negative charge increase or decrease in going from the points Q and P; A and B. Explain to P. Explain charge from B to A. Explain B to A? Explain
Explanation / Answer
A) Electric field E = kq/r^2
- 150 = 9e9*q/6.371e6^2
q = - 150*6.371e6^2 /9e9
= - 676494 C
Charge density = q/(4piR^2)
= -676494/(4*pi *6371000^2)
= - 1.326*10^-9 C/m^2
B) charge = - 676494 C
