Electronic Trainer Combined Series and Parallel Circuits In this lab you will work with a circuit combining series and parallel elements. You will use six resistors to create a circuit with two parallel resistor pairs connected with two series resistors. You will then apply a DC voltage to the circuit and measure the current through and voltage across each resistor. These measurements will be used to verify Kirchoff s loop and junction rules. R 1 R 4 Ground 5.0V R 2 R 3 R 5 R 6 Purpose: The purpose of this lab is to investigate the relationship between current and voltage in a combined series-parallel circuit. Equipment: Digital multimeter Electronic Trainer Resistors Cautions: This equipment is delicate. Everything should go together with the lightest of touches. Do not force anything! Familiarization with the Electronic Trainer and initial circuit setup: 1. Look at the white breadboard on the Electronic Trainer. Notice the blue horizontal row labeled - at the top. This will be used as a common ground connection, or ground bus, for this lab. Also notice the red horizontal row labeled +, below the blue horizontal row. The red-labeled row will be used as a common source of positive potential (voltage), or power bus, throughout this lab. Any wire connected to any socket along one of these horizontal rows is at the same voltage with any other socket on the same row. 2. To the left where it says REGULATED POWER SUPPLY is a four socket strip labeled GND. Run a wire from the GND to a socket on the ground bus (horizontal blue line). This supplies a ground for the ground bus. 3. Above the fuse is four socket strip labeled +5. Run a wire from one of these four sockets to a socket in the positive bus (horizontal red line). This supplies a constant voltage for the power bus. TOPS Electronic Trainer Combined Series and Parallel Circuits.doc Page 1
4. Below the power bus there are two banks of breadboard sockets, rows labeled a through j, and columns labeled 1 through 63. For any numbered column, the five sockets a through e are connected to each other, and the five sockets f through j are connected to each other as well. The a-e sockets are NOT connected to the f-j group. 5. Run a wire from socket 6a to the power bus (the horizontal red line at the top). This supplies power to sockets 6a through 6e 6. Connect a 2200 ohm resistor (color code red, red, red) from 6e to 6h. This is resistor R 1. 7. Run a wire from socket 6j to socket 20b. 8. Connect another 2200 ohm resistor (3 red stripes again) from 20e to 30e. This is resistor R 2. 9. Connect a third 2200 ohm resistor from 20a to 30a. This will be called R 3. 10. Connect 20d to 35f with a jumper wire. 11. Connect 30c to 55h with a jumper wire. 12. Connect 40h to 45h with a jumper wire. 13. Connect one more 2200 ohm resistor from 35j to 40j. This will be called R 4. 14. Connect 55i to the ground bus at the top of the breadboard. 15. Connect a 1000 ohm resistor (color code brown, black, red) from 45j to 55j. This will be called R 5. 16. Connect another 1000 ohm resistor from 45f to 55f. This will be called R 6. Measuring voltages: 1. Plug the red meter lead into the V terminal on the lower right face of the multimeter. Double-check to make sure that the red lead is in the V socket! 2. Plug the black meter lead into the COM terminal. 3. Set the dial at 20 in the V section (upper right hand corner). 4. Turn the Trainer power supply on (red toggle switch, lower left hand corner). The circuit is now live, but the voltage is low so there is no danger of shock. You should be careful not to short out the circuit, however, as this could damage the trainer. Follow the next instructions carefully: Measuring Voltage across R 1: 5. Touch the red meter lead to R 1 at 6e and the black multimeter lead to R 1 at 6h. Measuring Voltage across R 2 : 6. Touch the red meter lead to R 2 at 20e and the black multimeter lead to R 2 at 30e. Measuring Voltage across R 3 : 7. Touch the red meter lead to R 3 at 20a and the black multimeter lead to R 3 at 30a. Measuring Voltage across R 4 : 8. Touch the red meter lead to R 4 at 35j and the black multimeter lead to R 4 at 40j. Measuring Voltage across R 5 : 9. Touch the red meter lead to R 5 at 45j and the black multimeter lead to R 5 at 55j. TOPS Electronic Trainer Combined Series and Parallel Circuits.doc Page 2
Measuring combined voltage across R4 and R5: 10. Touch the red meter lead to R 4 at 35j and the black multimeter lead to R 5 at 55j. Measuring Voltage across R 6 : 11. Touch the red meter lead to R 6 at 45f and the black multimeter lead to R 6 at 55f. Measuring combined voltage across R4 and R6: 12. Touch the red meter lead to R 4 at 35j and the black multimeter lead to R 6 at 55f. 13. Return the dial on the multimeter to 0 (Off). You have now found all the voltages across all the resistors, and are ready to go on to the current measurements. Caution when using the current measurement terminals on the multimeter ( A or µama ). DO NOT apply the meter leads across any voltage source without a series resistance! Applying live voltages to the current terminals of the multimeter will destroy fuses inside. You must ONLY make current measurements by making the multimeter (ammeter) a series part of the circuit. For this part of the lab you will disconnect one end of each resistor, in turn, and connect the multimeter red lead to the free end of the resistor and the black lead of the multimeter to a medium length of spare wire that replaces the end of the resistor in the breadboard socket. Measuring currents through the resistors: In order to measure current through a component, the ammeter must be placed in series with that component. 1. Check to see that the black lead of the multimeter is still connected to the COM terminal. 2. Move the red multimeter lead connection to the µama terminal. 3. Set the multimeter dial to 2m/2A. Measuring Current through R 1 : 4. Remove one end of R1 from 6h (do not let it drop into any other socket, and do not disconnect 6e). 5. Place one end of a spare jumper wire in 6h. 6. Measure the current through R 1 by connecting the red meter lead to the free end of R1 and the black meter lead to the free end of the wire inserted in 6h. 7. Remove the spare jumper wire from 6h and replace the free end of R1 into 6h. To find the current through R 2 : 8. Remove one end of R2 from 30e, 9. Insert the spare wire in 30e, 10. Measure the current as before, red meter lead to the free end of R2, black lead to the wire replacement in 30e. 11. Remove the spare wire from 30e and replace the free end of R2 into 30e. TOPS Electronic Trainer Combined Series and Parallel Circuits.doc Page 3
To find the current through R 3 : 12. Remove one end of R3 from 30a, 13. Insert the spare wire in 30a, 14. Measure the current as before, red meter lead to the free end of R3, black lead to the wire replacement in 30a. 15. Remove the spare wire from 30a 16. Replace the free end of R3 into 30a. To find the current through R 4 : 17. Remove one end of R4 from 40j 18. Insert the spare wire in 40j, 19. Measure the current as before, red meter lead to the free end of R4, black lead to the wire replacement in 40j. 20. Remove the spare wire from 40j 21. Replace the free end of R4 into 40j. To find the current through R 5 : 22. Remove one end of R5 from 55j 23. Insert the spare wire in 55j, 24. Measure the current as before, red meter lead to the free end of R5, black lead to the wire replacement in 55j. 25. 26. Remove the spare wire from 55j 27. Replace the free end of R5 into 55j. To find the current through R 6 : 28. Remove one end of R6 from 55f, 29. Insert the spare wire in 55f, 30. Measure the current as before, red meter lead to the free end of R6, black lead to the wire replacement in 55f. 31. Remove the spare wire from 55f 32. Replace the free end of R6 into 55f. Cleanup: 1. Return the multimeter dial to 0 (Off), 2. Return the red multimeter lead to its original terminal. 3. Turn the Trainer power supply switch to Off (red toggle switch, lower left hand corner). 4. Remove all components and make sure that everything is as you found it. 5. Transfer all your voltage and current measurements to the table below. 6. Compute the power consumed by each resistor by multiplying the voltage and current values for that resistor; filling in the Power column as you go. TOPS Electronic Trainer Combined Series and Parallel Circuits.doc Page 4
Resistor Voltage Current Power R 1 R 2 R 3 R 4 R 5 R 6 Data analysis: Does your data support Kirchoff s Loop Rule? All voltages around closed loops should add up to zero. For example, the supply voltage minus the voltage drop in R 1 minus the voltage drop in R 2 should equal zero. The same should hold for all loops. Show at least three calculations below that demonstrate Kirchoff s loop rule using the data collected in this experiment: Does your data support Kirchoff s Junction Rule? The sum of the currents entering a junction should equal the sum of the currents leaving a junction. For example, the current leaving resistor R 4 should equal the sum of the currents entering R 5, and R 6. The same should hold for all junctions. Show at least three calculations below that demonstrate Kirchoff s junction rule using the data collected in this experiment: TOPS Electronic Trainer Combined Series and Parallel Circuits.doc Page 5
Does your data support the conservation of energy? The power produced by the battery should equal the power consumed by the resistors. Show that this is so using the data you collected. Hint: All of the current from the battery goes through R 1! If this circuit runs for 10 minutes, how much energy is consumed? TOPS Electronic Trainer Combined Series and Parallel Circuits.doc Page 6