Week 5

Read: This week I will be lecturing on electronic circuits. In particular, we will explore Ohm's law and Kirchoff's rules, and learn how to build and analyze elementary electronic circuits.
Quiz: Monday.


  1. High-voltage power lines deliver electrical current to your neighborhood. The aluminum wire used for these lines has a cross sectional area of about 5 square centimeters. What is the resistance of ten kilometers of this wire? Hint: you will need to look up the resistivity of aluminum. Answer: since the resistivity of Aluminum is 2.65e-8 Ohm-meters, we get a total resistance of 0.53 ohms
  2. A car battery has a rating of 220 ampere hours. This rating is one indication of the total charge that the battery can provide to a circuit before failing. What is the total charge (in coulombs) that this battery can provide? What is the maximum current that the battery can provide for 38 minutes. Answer: 220 amperes * 1 hour = 792,000 Coulombs. (You need to convert hours to seconds). Dividing this charge by 38 minutes we get a maximum current of 347 Amperes (this is huge).
  3. The current in a series circuit is 15.0 amperes. When an additional 8.00 ohm resistor is inserted in series, the current drops to 12.0 amperes. What is the resistance of the original circuit? Answer: since we are using the same battery, the voltage drop across the circuit is the same in both cases. So we know 15.0 amperes * R = 12.0 amperes * (R + 8). Solving for R, we get 32 ohms.
  4. Eight different values of resistance can be obtained by connecting together three resistors (1, 2 and 3 ohms) in all possible ways. What are they? All in series: 6 ohms; 3 in series with 1&2 in parallel: 11/3; 2 in series with 1&3 in parallel: 11/4; 1 in series with 2&3 in parallel: 11/5; 1 in parallel with 2&3 in series: 5/6; 2 in parallel with 1&3 in series: 4/3; 3 in parallel with 1&2 in series: 3/2; all three in parallel: 6/11
  5. Electromotive force and ohms law (ASGv3Ex25.1)

DC Circuits laboratory

Physics 2