Lab 9 (Ohm\'s Law) - Richard Youngworth lab. PDF

Preview

Summary

Richard Youngworth lab....

Description

Individual Report: Ohm’s Law Analysis of Results: The results were expected in that our resistor values, when they were placed in series, matched so that the overall equivalent resistance was the addition of the two values, and when they were placed in parallel it was the inverted sum of each inverted resistance. The error was small for the resistance value for the second resistor, the resistors in series, and the resistors in parallel, as it was 2.1%, 3.4%, and 3.8% respectively. However, the error was large for the measurement of the first resistors resistance, as it was 28.6%. This experiment was valid because we accomplished the experimental objective of verifying Ohm’s Law and using it to verify equivalent resistance of series and parallel circuits. The major trends in the data were that for parallel circuits the equivalent resistance decreased, and for circuits in series the equivalent resistance increased. Also, for the series with light bulbs, adding more light bulbs into the series required more volts to reach the same brightness, and that discontinuing a part of the circuit resulted in anything connected to it in series (as long as it didn’t have any part in parallel) to no longer receive potential. The practical implications of these results are that it has become easier to understand/see how Ohm’s law works, and how circuits, in addition to their parts, function. Actually observing the phenomena of Ohm’s law and functioning circuits in real life and not just in equations or simulations helps me to understand the way it affects objects in the world around me. Improvement: The major sources of error in this experiment came from random error from the instruments. Although, this error would be extremely difficult to negate and the core message of the lab was not hindered because of this error. It is not reasonable to purchase new equipment, since our results were very close to their actual value, and the error did not take away from the take-home message of the lab. Especially since we are not using “ideal” equipment, such as ideal wires that offer no resistance and so on. There was one huge error, though, in our first resistor measurement, and we are unsure of the cause of it. The DMM measured the resistor to have a resistance of 2170 ohms; however, this value must have been incorrect because our experiment we did calculated it to be about 1500 ohms. Also, assuming the 1500 ohm measurement was correct, it led all of our equivalent resistance measurements for parallel or series circuits to be very accurate. Our data would support that the resistance was actually about 1500 ohms, but for some unknown reason this did not agree with the DMM measurement, even though the DMM measurement was correct for the other resistors tested. Individual Questions: To answer the first question: the error for each resistor and circuit is discussed above, and as previously stated in the above section, systematic error is implied from the error obtained. The second question, like the first, has already been discussed in the improvement section in regards to source of error. For the third question, as the voltage increased to the light bulb, the current ended up increasing in a non-linear fashion. The resistance decreased as the voltage increased such that more power was dissipated and more heat was given off as the bulb got brighter. The

resistance therefore decreased with increasing temperature. The bulb does not follow Ohm’s law because the current and voltage are not linearly related. For the fourth question, the bulbs had varying brightness even when the voltage was the same because current was not consistent even if voltage was. The brightness would change or go out when other bulbs were altered because if more bulbs are introduced it will affect the current. When A burned out, the circuit was no longer closed so the circuit did not have current flowing through it so A and all the bulbs after it were out. When and B were in series, the voltage remained constant, but the total resistance increased so the current decreased and the bulbs became less bright (compared to A by itself) since less power could be dissipated. When A was in series with B+C which were in parallel, B and C were not as bright as A because their resistance was higher. When either C or B burnt out, the same thing happened because they were equivalent and were in parallel with one-another such that when one went out, the other became brighter and was just as bright as A, but both were dimmer than A originally since they are not equivalent so when A and B were in series (it is the same setup)....