Hannah's+Resistive+Circuits+Lab

=Resistive Circuits Lab= February 8, 2010


 * Participants**: Hannah Mollmark
 * Purpose**: The purpose of this lab is to construct, observe, and understand electric circuits. Using resistors helps to understand their function as well. Comparing voltage and current allows for the understanding of resistance and its correlation to voltage and current.


 * Brief Description of Experiment**: In this experiment, we created circuits in order to understand voltage, current, and resistance. In addition to creating these in class, we also used a simulation online. We used wires, batteries, light bulbs, resistors, alligator clips, and multimeters. For part 1, we had a basic circuit with one resistor. For part 2, we created a circuit with a light bulb. Part 3's circuit had three resistors in series; whereas, part 4's circuit had three resistors in parallel. Part 5 combined these ideas and had four resistors in series and parallel formation. (Pictures of the simulations are shown in the data section below.)

The graph and chart shown below are that of __Activity 1: Measuring the resistance of a resistor__. In this part of the lab, we created a simple circuit with one resistor. The results, which are graphed, display that as the resistor voltage increases so does the current and vice versa. The resistance is equal to the voltage divided by the current, so the higher the voltage, the greater the resistance. In contrast, the higher the current (or lower the voltage), the lesser the resistance. The resistance calculated from the different trials (using the resistance = voltage / current equation) are shown in the last column of the chart. The resistance calculated from the slope of the line fit to the data on the graph is 8.21 ohms; this was found by using the equation slope = 1 / resistance. By comparing these resistances, one can see that the resistances from the trials are very close to the resistance calculated from the best fit line from the graph. The graph and chart shown below are that of __Activity 2: A non-Ohmic device__. In this part of the lab, we put together a simple circuit with a light bulb. As with the results from activity 1, the graph shows that as the resistor voltage increases so does the current and vice versa. The fourth column shows the resistances that were calculated by using Ohm's Law equation (I = V/R) and the resistance calculated from the graph (using the equation slope = 1 / resistance) is shown below the chart. Unlike activity 1, the trial resistances are varying and do not match the resistance calculated from the best fit line from the graph. This is because the resistance is voltage dependent so it's not a constant for any voltage. The line doesn't fit the data points as well as for activity 1, so the proportion between current and voltage isn't linear.
 * Data**:



The picture shown below is that of __Activity 3: Three series resistors__. In this part of the lab, we tested the current and resistor voltages with two different target battery voltages in a series circuit. When the battery voltage was higher so was the current and the resistors' voltages. The target voltage was doubled resulting in the current and resistor voltage values to be doubled as well. The current flowing through the circuit remained the at the same speed. In contrast, the voltage across the three resistors in the circuit are different, but if you add up the resistor voltages you will get a number very close to the battery voltage. The resistances of the resistors that were calculated by using the Ohm's Law equation (I = V/R) were very close to the resistances that were manually put into the simulation. We made the resistances 10ohms, 6.7ohms, and 46ohms. The calculated resistances were 0.101ohms, 0.065ohms, and 0.462ohms. (Note: Resistor 1: green, copper, brown, back, brown; Resistor 2: yellow, purple, redish brown, gold; Resistor 3: dark blue, light blue, black, yellow-gold)

The picture below is that of __Activity 4: Three parallel resistors__. In this part of the lab, we tested the battery current and resistors' currents with two target voltages in a parallel circuit. When the battery voltage was higher so was the battery current and resistor currents. In contrast to the series circuit in activity 3 where the current was constant and the resistor voltages added up to the battery voltage, in a parallel circuit, the voltage should be constant and the resistor currents should add up to the battery current. The resistances calcuted using Ohm's Law equation (I = V/R) were 0.112ohms, 0.473ohms, 0.076ohms are very close to the given battery resistances of 10ohms, 46ohms, and 6.7ohms. The reason for the difference in currents in the different resistors is due to the direction of electrons in the circuit. Unlike the series circuit where the electrons have no choice as to what direction they travel, in a parallel circuit they have three choices as to which "branch" of the circuit they travel down and therefore which resistor they flow through. (Note: Resistor 1: green, copper, brown, back, brown; Resistor 2: yellow, purple, redish brown, gold; Resistor 3: dark blue, light blue, black, yellow-gold)

The picture below is that of __Activity 5: Parallel and series__. In this part of the lab, we created a circuit with resistors in parallel and series and took note of the voltage and current of all four resistors. Unlike the previous activities, we did not compare two different battery voltages so that cannot be compared. The observable pattern is that resistors 1 and 4 are very close in voltage and current values because they are in series (the voltages are still the same because they aren't next to each other so they are more like individual resistors), and resistors 2 and 3 are very close in voltage values because they are in parallel. The current values of 2 and 3 are different because parallel resistors have varying currents (as explained above). The resistance for resistor 1 is 0.102 ohms, resistor 2 is 0.500 ohms, resistor 3 is 0.066 ohms, and resistor 4 is 0.104 ohms. (Note: Resistor 1: brown, black, brown; Resistor 2: yellow, violet, brown; Resistor 3: blue, gray, black; Resistor 4: brown, black, brown)

current = voltage / resitance I = V / R If the equation is rearranged, the resistance can be found by dividing the voltage, in volts, by the current, in amps. resistance = voltage / current R = V / I slope = 1 / resistance m = 1 / R || I believe that the experiment produced a valid and reproducible result especially with the use of the simulations in order to create more exact results. My experimental results differ from accepted or expected results because of the normal human error of reading the measurements and rounding numbers in calculations. One thing we noticed in conducting the experiment was when we were measuring the voltage, the reading on the multimeter kept dropping and we weren't sure what measurement to take; this could very likely have caused an error in our results. Using the simulations as a comparison to the real circuits results made up for these errors.
 * Sample Calculations:**
 * //Current calculation// || The current in amps is calculated by dividing the voltage, in volts, by the resistance, in ohms.
 * the slope of the line on the current vs voltage graph is equal to 1/resistance
 * Results**: From this lab I learned a lot about creating circuits and about the different parts and behaviors. Ohm's Law explains the relationship between current, voltage, and resistance in that current is equal to the voltage divided by the resistance (I = V/R). I also learned that in a series circuit, the current is constant through resistors and the voltage is different; whereas, in a parallel circuit, the voltage is constant through the resistors and the current is different. In setting up these different circuits hands on in real life I was able to fully understand how the connections are made and how electrical circuits work. In doing the simulation online, I was able to further my understanding by seeing the expected values and results for the experiment.
 * Conclusion**: Current is the motion of electrons through a circuit moving from wire to battery to resistor (and other parts of the circuit). Voltage is the electric potential energy per unit charge. Current, which is measured in amps, and voltage, measured in volts, are related in their behavior in circuits. The current in a series circuit is the same throughout the circuit, but the voltage is different. The voltage of each part of the circuit will be less than the battery voltage but added together, it will equal the battery voltage. In a parallel circuit, the current will be different to each part, but the voltage is equal to all parts of the circuit. Resistance is the measure of how much an object opposes the steady movement of electrons through a circuit. Resistance relates current and voltage in respect to Ohm's Law which states that the current across two points is directly proportional to the voltage across those two points as well as inversely proportional to the resistance between those points. The differences that I found between the simulated circuits and the real circuits included more exact measurements of the voltage and current.