Download Electrostatics Problem Set: Coulomb's Law and Electric Forces and more Assignments Astronomy in PDF only on Docsity! 299 HW01 (Questions 1-6) Due in Lecture on 09/07/05 NAME________________________________________________________ (please print) 1. (Problem 21.7 from the book) Two small plastic spheres are given positive electrical charges. When they are 0.15cm apart, the repulsive force between them has magnitude 0.22N. What is that charge on each sphere if a) the charges are equal? b) if one sphere has four times the charge of the other? (5 points) 1 2. (Problem 21.73) Sodium Chloride (NaCl) is made up of positive ions (Na+) and negative clorine ions (Cl-). (a) If a point charge with the same charge and mass as all of the Na+ ion in 0.100 mol of NaCl is 2.0 cm away from a point charge with the same charge and mass as all the Cl-, what is the magnitude of the attractive force between these two points charges. (b) If the positive charge is released from rest, what is its initial acceleration? (See appendix D for atomic masses or use google to look them up.) (c) Does it seem reasonable that the ions in NaCl could be separated in this way? Why or why not? (In fact, when sodium chloride dissolves in water it breaks up into Na+ and Cl- ions. However, in this situation there are additional electric forces exerted by the water molecules on the ions.) (5 points) 2 5. Two charges of magnitude -4Q and -4Q are placed at diagonally opposite corners, B and D, of a square ABCD, of side length x. A third point charge of unspecified magnitude is placed at A, where it is observed that it experiences a resultant force caused by its electrostatic interaction with the charges at B and D. Calculate, in terms of Q, x, and the Coulomb constant 10 )4( −= πεk , the value of the fourth charge that would have to be placed at C in order to reduce the resultant force on the charge at A to zero. (Note: use the set up below when you draw a diagram; this question is nudging you towards the idea of electric field strength)(3 points) A B C D x 5 6. A mass M hangs vertically from a plastic, non-conducting string as shown in the diagram. The string passes over a frictionless pulley and then horizontally through an insulating tube, as shown. On the other end of the hanging mass is a spring with spring constant k. This spring is initially in equilibrium. A particle with a positive charge 5Q is attached to the end of the string, as shown. The string passes through a hole in a small charged sphere which also carries a positive charge 2Q. This second charge is fixed in the tube and thus cannot move; thus the distance between the two charges in the tube varies as the mass is moved up or down. M Charge = 2Q which is attached to the end of the rope Charge = 5Q which is fixed in the tube but allows the rope to pass through a hole in it. Frictionless pulley Smooth insulating tube ks The mass M is slowly lowered until the system is in static equilibrium with the mass hanging freely. Find an expression for the distance, d, between the two charges in the tube when the system is in static equilibrium. (Ignore the mass of the string and any frictional effects. Treat all charges as point charges.). (5 points) Solve for d and get 2 bonus points on quiz 1. 6
