Electric lab

Resistors in Series and Parallel Name: Tianyang Dong Lab Partner(s): Purpose Investigate some of the characteristics of series and parallel circuits as you measure the potential difference, current, resistance, and calculate the power of the same bulb on both circuits. Discussion There are two basic ways to connect more than one resistance in a circuit, in a series circuit or in a parallel circuit. A series circuit has each resistance connected one after the other so the same charges flows through one resistance, then the next one, and so on. A parallel circuit has separate pathways for the charges so they do not go through on resistance after the other. The use of the term” parallel” means that charges can flow through one of the branches, but not the others. The term does not mean that the branches are necessarily lined up with each other. The series and parallel circuits have separate characteristics that offer certain advantages and disadvantages. Equipment • • • • • 1 6 volt power supply 3 flashlight bulbs (1.5 volt) in sockets on a wooden platform 6 hook up wires Electronic Multimeter Calculator – student supplied How to measure voltage Voltmeters measure voltage change between two points in a circuit and are connected in parallel in order to measure the difference in potential between two points. Be sure you connect the negative terminal of the voltmeter to the negative side of the circuit. Correct Incorrect Note that you do not connect the voltmeter in series with the circuit such that the circuit current runs through it. This can potentially damage your voltmeter because voltmeters are not designed to have high currents running through them, and they will not measure your voltage change connected in this way. How to measure current Ammeters measure current and are connected in series so the measured current passes through them. Correct Incorrect Note that you do not connect the ammeter in parallel (or across) an element for which you’re wanting to measure the current, because then all of the current will pass through the ammeter rather than the circuit element. Think of the ammeter like a wire. If you connect it in series, you have created a short and the current will bypass the circuit element. Part I: Resistors in Series Adding more resistance in a series circuit results in two major effects: (1) decrease in the current available to the circuit, and (2) a reduction of the voltage available for each resistance. Since power is determined from V x I, adding more lamps (more resistance) will result in dimmer lights. Another disadvantage to a series circuit is that if one bulb burns out the circuit is broken and all lights go out. Procedure 1. Connect the power supply, switch, and bulbs in series as shown below. 2. Measure the voltage drop across and the current running through each bulb, as well as the voltage drop across and current running through the entire circuit. Record your measurements in the data table. Series Circuit Data Table Element Volts (V) Amps ( A) Resistance Power (W) Bulb 1 1.5 0.9 1.66 1.35 Bulb 2 1.5 0.9 1.55 1.26 Bulb 3 1.5 0.9 1.55 1.26 Circuit 4.3 1.9 4.77 3.87 3. Calculate and record the resistance and the power of each bulb and for the entire series circuit. Show a sample of your work. R=I/V=1.5/0.9=1.66 P= IV P= 0.9×1.5=1.35 4. Should current 4 agree with any other measurement? Explain. 5. Remove one of the bulbs from the series circuit and record here the effect on the other bulbs. When one of the bulbs is removed, the circuit could not turn on. Part II: Resistors in Parallel Adding more resistance in a parallel circuit results in three major effects: (1) an increase in the current in the circuit, (2) but the same voltage is maintained across each resistance, and (3) lowering the total resistance of the entire circuit. The total resistance is lowered since more pathways are provided for the moving charges, the current. 1. Connect the three bulbs in parallel as shown below. 2. Measure the voltage drop across and the current running through each bulb, as well as the voltage drop across and current running through the entire circuit. Record your measurements in the data table. Parallel Circuit Data Table Element Volts (V) Amps ( A) Resistance Power (W) Bub 1 5.3 160 3.3125 8.48 Bulb 2 5.3 160 3.3125 8.48 Bulb 3 5.3 160 3.3125 8.48 Circuit 5.3 160 3.3125 8.48 3. Calculate and record the resistance and the power of each bulb and for the entire parallel circuit. Show a sample of your work starting with the correct relationship. 4. Remove one of the lamps from the parallel circuit and record the effect on the other bulbs. No effect, all the bulbs will still remain on, because they are connected to the power supply directly. Analysis: 1. How does the voltage drop of each of the three bulbs in the series circuit compare with the voltage of the source? 2. How does the voltage drop of each of the three bulbs in the parallel circuit compare with the voltage of the source? 3. How does the current through one bulb in the series circuit compare with the total current through the three lamps? 4. How does the current through one bulb in the parallel circuit compare with the total current through the three lamps? 5. Account for any differences in brightness observed by the same bulbs in series and parallel circuits. 6. According to the results of this investigation, what happens to the current and voltage available for each resistance as more resistance is added to a series circuit? 7. According to the results of this investigation, what happens to the current and voltage available for each resistance as more resistance is added to a parallel circuit? 8. Write a few statements about this lab stating what if anything improved your understanding of the concepts, what was the most difficult part, what did you like the most and what did you dislike the most. Extra Credit Discussion: Frequently, multi-story homes have hallways with ceiling lights. It is convenient if you can turn a hallway light on or off from a switch located at either the top or bottom of the staircase. Each switch should be able to turn the light on or off, regardless of the previous setting of either switch. In this activity you will see how simple but tricky such a common circuit really is! Equipment: • • • • 2 double throw switches – this means they are on when the switch is in either position. Four or more wires Batteries in the holders Light bulb in fixture Procedure: 1. The best approach comes by carefully thinking about what you want to accomplish and perhaps even sketching out the wiring you test. Change the sketch as you move from attempt to attempt. 2. Draw a simple circuit diagram of your successful circuit. Use the standard symbols: 3. Connect your circuit and demonstrate to the lab instructor that it can turn the bulb on or off from either switch. Instructor initials for extra credit____________

Electric lab

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