Problem 1. A 9.0 V battery is connected across a 1.25 k resistor. (a) How many electrons flow into (and out of) the resistor each second? (b) What is the power dissipated by the resistor? Problem 2. Copper has a mobile electron density of 8.46 x 1028 electrons per cubic meter and a resistivity of 1.68 x 10-8 0m. You have a copper wire that is 1.00 m long and has a circular cross-section with a radius of 1.00 mm. (a) What is the resistance of the wire? (b) If the wire carries a current of 15.0 mA, what is the corresponding drift velocity va of mobile electrons in the wire? Problem 3. Use the rules for combining series and parallel resistors to find the total equivalent resistance between points A and B in each of the two circuits shown below. (In other words, what resistance would you measure if you connected an ohmmeter to points A and B?) 88 0 A 85 S A 112 0 150 0 75 02 2 45 02 B 125 02 50 02 (a) B (b) 55 02 Problem 4. You connect an adjustable DC voltage source across two series resistors with resistances Ri = 150 0 and R2 = 250 0. Each resistor is rated for a maximum power dissipation of 0.25 W, meaning that the resistor may burn out if you exceed this value. Beginning at Vo = 0 V, you gradually increase the value of the DC voltage source until the total power dissipated by one of the resistors reaches 0.25 W. Which resistor reaches 0.25 W first, and what is the value of the source voltage Vo when this occurs? Problem 5. For the circuit shown below, find (a) the total power dissipated in the circuit and (b) the power dissipated in the 75 0 resistor. 25 0 1.5 V > 75 0 45 0 55 0