Test: Voltage, Current and Resistance
Goals and Review

1. Calculate the force between a charge of +5.0 nanocoulombs and -12 microcoulombs, separated by a distance of 15 millimeters? Is the force attractive or repulsive? An attraction force of 2.4 Newtons

2.  In this picture, put a plus sign next to the positive charges, and minus sign next to the negative charges.
They are all positive, except the top-most charge is negative.

3. What is the total energy that can be delivered by a 1.2-volt rechargable battery with a capacity of 9000 coulombs of charge before needing a recharge? 10,800 Joules

4. You find a very patriotic resistor with the following stripes: red-white-blue. What is its value and tolerance?
              29,000,000 Ω, or 29 MΩ. Since it doesn't have a fourth stripe, it's only guaranteed to have an actual resitance within 20% of this specified value

5. A resistor is connected to a 9V battery, and the resulting current is 250 mA. What is the resistor's resistance? 36 ohms

6. What color stripes should a 5.6 kΩ resistor have? It's tolerance is 10%. Green-Blue-Red-Silver

7. If you connect the resistor from the previous problem to the 1.2-volt battery, how much current will flow?
               0.00021 A, which you can also write as 0.21 mA, or 210 µA.

8. You have three 100Ω resistors. What are all the possible resistances you could make by combining those resistors? Draw each arrangement. Which arrangement, if connected to a battery, would draw the least current from the battery?

300 ohms (all three resistors in series)
33 ohms (all three resistors in parallel)
150 ohms (1 resistor in series with a parallel combination of the other two)
67 ohms (1 resistor in parallel with a series combination of the other two)

The all-in-series combination will draw the least current from the battery, because it has the highest total resistance.

9. Two resistors are in series, 220 ohms and 1 kilohm, hooked up to a 9-volt battery.
(a) What current will flow through the 220-ohm resistor? 7.4 mA
(b) What current will flow through the 1-kilohm resistor? 7.4 mA
(c) What will be the voltage drop across the 220-ohm resistor be? 1.6 V
(d) What will be the voltage drop across the 1-kilohm resistor be? 7.4 V

10. What is a relay? An electrically-operated switch.

11. What's another name for a variable resistor? Potentiometer

12. Draw a circuit that contains a 9-volt battery in series with a 200-ohm resistor. This is connected to three other resistors wired in parallel. The three parallel resistors are 300, 400 and 500 ohms. (a) What is the total current flowing out of the battery? (b) What is the current through each of the 4 resistors? (c) Which resistor is using the most power, and how much power is it using? (d) If you removed one of the parallel resistors from the circuit, what would happen to the current coming from the battery? Watch the solution video.

13. The label on the table saw in our classroom says "120 VAC 60 Hz 13 A". (a) What does all that mean? (b) What power ("wattage") does it use when running? The saw runs on standard U.S. wall outlet electricity, 120 volts, alternating current, oscillating 60 times per second. The maximum current the saw draws is 13 amperes. The power used by the saw is, at most, 1560 W, or rounded, 1.6 kW.

14. You connect a 9-volt battery to a capacitor, and determine that 27 nanocoulombs of charge are stored on the capacitor as a result. (a) What is the capacitance? 3 nF (b) If that capacitor is instead connected to two 9-volt batteries wired in series, what charge will be stored? The voltage will be twice, i.e. 18 V, and because charge is proportional to the voltage, the cap will store twice the charge. 54 ncoul. (c) If five such capacitors are wired in parallel, will the combination be able to store more charge, less charge, or just the same amount of charge as the single capacitor? More; capacitance just adds for caps in parallel, so the capacitance will be 15 nF. Connected to the single 9V battery, the parallel combination of 5 caps will store 135 ncoul.