Physics 202, Homework #5 Due: 10/24/2013 at 10:50 AM 1. The figure gives the drift speed vd of conduction electrons in a copper wire versus position x along the wire. The wire consists of three sections that differ in radius. Rank the three sections, according to the following quantities, greatest to least: (a) radius, (b) the magnitude of the electric field, and (c) conductivity. Explain your answer. (6 points) 2. Three wires of the same diameter are connected in turn between two points maintained at a constant potential difference. Their resistivities and lengths are r and L (wire A), 1.2r and 1.2L (wire B), and 0.9r and L (wire C). a. How does the rate at which energy is transferred to thermal energy vary with the resistance of the wire? In other words, does the dU/dt increase with increasing resistance or does it decrease with increasing resistance? Remember, the potential across each wire is the same. Explain. (2 points) b. Using your answer from part (a), rank the wires according to the rate at which energy is transferred to thermal energy within them, greatest to least. (1 point)
3. In the figure below, R1 = R and R2 = R/2, and the ideal batteries have emfs E1= 5E , and E2 = E3 = E. Assume that the direction of the currents i1, i2, and i are indicated by the blue arrows. Unless stated otherwise, put all answers in terms of R and E. a. What is the potential difference across R1? Hint: you do not need to do any math to figure this out. (1 point) b. What is the current through R1? (1 point) c. What is the potential difference across R2? (1 point) d. What is the current through resistor R2? (1 point) e. Use the Kirchoff’s current law to find an equation that relates the currents i, i1, and i3. (1 point) f. Apply Kirchoff’s laws to this circuit and obtain three independent equations. Put all equations in terms R, E, i1, i2, and i. (3 points). Assume that the direction of the current is indicated by the blue arrows. g. Does the current i2 go upward or downward…