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KEY Circuits Worksheet Multiple Choice ____ 1. The following three appliances are connected in series to a 120 V house circuit: a toaster, 1200 W; a coffee pot, 750 W; and a microwave, 6.0 102 W. If all were operated at the same time, what total current would they draw? a. 3 A c. 10 A b. 5 A d. 21 A ____ 2. Three resistors connected in series carry currents labeled I1, I2, and I3, respectively. Which of the following expresses the total current, It, in the system made up of the three resistors in series? a. It = I1 + I2 + I3 c. It = I1 = I2 = I3 b. It = (1I1 + 1/I2 + 1/I3) d. It = (1I1 + 1/I2 + 1/I3)–1 ____ 3. Three resistors connected in parallel have voltages labeled V1, V2, and V3. Which of the following expresses the total voltage across the three resistors? a. Vt = V1 + V2 + V3 c. Vt = V1 = V2 = V3 b. Vt = (1/V1 + 1/V2 + 1/V3) d. Vt = (1/V1 + 1/V2 + 1/V3)–1 ____ 4. Three resistors with values of R1, R2, and R3 are connected in series. Which of the following expresses the total resistance, Rt, of the three resistors? a. Rt = R1 + R2 + R3 c. Rt = R1 = R2 = R3 b. Rt = (1/R1 + 1/R2 + 1/R3) d. Rt =(1/R1 + 1/R2 + 1/R3)–1 ____ 5. Three resistors with values of 3.0 , 6.0 , and 12 are connected in series. What is the equivalent resistance of this combination? a. 0.58 c. 7.0 b. 1.7 d. 21 ____ 6. Three resistors with values of 4.0 , 6.0 , and 10.0 are connected in parallel. What is their equivalent resistance? a. 20.0 c. 6.0 b. 7.3 d. 1.9 ____ 7. Two resistors with values of 6.0 and 12 are connected in parallel. This combination is connected in series with a 4.0 resistor. What is the overall resistance of this combination? a. 0.50 c. 8.0 b. 2.0 d. 22 ____ 8. Three resistors with values of 18 , 26 , 9 , respectively, are connected in series. What is their equivalent resistance? a. 9.2 c. 60 b. 53 d. 13 ____ 9. Three resistors with values of 15 , 41 , 58 , respectively, are connected in parallel. What is the overall resistance of this combination? a. 9.2 c. 60 b. 53 d. 13 ____ 10. Two resistors with values of 6.0 and 12 are connected in parallel. This combination is connected in series with a 2.0 resistor and a 24 V battery. What is the current in the 2.0 resistor? a. 2.0 A c. 6.0 A b. 4.0 A d. 12 A Short Answer 11. What is the equivalent resistance for the resistors in the figure above? First, combine the 6 Ω and the 10 Ω resistors, which are in series This combined resistance is in parallel with the 4 Ω resistor Finally, the combined resistance of the three resistors combined so far is in series with the last 2 Ω resistor 12. What is the equivalent resistance for the resistors in the figure above? The top three resistances are in series, which means their total resistance is 9 Ω. This combined resistance is in parallel with a 3 Ω resistor. 2 13. What is the equivalent resistance for the resistors in the figure above? The top two resistors are in series. This combined resistance is in parallel with the 4 Ω resistor Finally, the combined resistance of the three resistors combined so far is in series with the last 5 Ω resistor 14. What is the total voltage drop across the entire above circuit? Since the voltage source provides 40 V, the total voltage drop across the circuit must equal 40 V 15. What is the total current in the circuit above? Ohm’s Law should be used to find the total current through the circuit, since the total voltage and total resistance is known. 16. Indicate the bulbs which will have a current in the schematic diagram above? 3 17. How much current is in one of the 10 resistors in the diagram shown above? The first step in this problem is to find the total resistance. The three resistances on the right of the diagram are all in parallel This combined resistance is in series with the 2 Ω resistor. The total resistance is therefore 6 Ω. Using Ohm’s Law, the total current is All of this current must flow through the 2 Ω resistor. Therefore, the voltage drop across this resistor is If the voltage drop across the 2 Ω resistor is 4 V, then the rest of the 12 V must drop across the three resistors in parallel. This voltage drop of 8 V allows for the calculation of the current through one of the 10 Ω resistors. 4 18. What would the current through the 2 ohm resistor in the figure above if 120V was applied across this resistance? The current that passes through the 2 Ω resistor is the same as the total current flow, since all of the current must flow through the 2 Ω resistor. The first step is to determine the combined resistance of the entire circuit. Fortunately, this circuit has already been analyzed in problem 11. Since the total resistance and total voltage is known, the total current can be found using Ohm’s Law 19. In the schematic diagram above, will there be a current? Yes. The circuit has a voltage source, resistance, and is unbroken. Therefore, current will flow. 5