course Phy 232
I am submitting these mainly because you have not yet recieved my test and I have not been able to contact the professor that proctored it. If by the time my school opens back up from break (Nov. 28)I have not heard back from him I am going to get someone else to proctor it again and I will take the test a second time. thank you for your patience
Good work on these experiments. See my note(s).
Let me know if there's anything you would like me to clarify, and include the specifics of what you do and do not understand.
Do keep me posted about the test.
I am submitting these mainly because you have not yet recieved my test and I have not been able to contact the professor that proctored it. If by the time my school opens back up from break (Nov. 28)I have not heard back from him I am going to get someone else to proctor it again and I will take the test a second time. thank you for your patience
Experiment 16: Current Flow and Energy
Clamp the ends of the leads coming from the generator to a piece of wood or plastic and turn the crank at about 2 complete turns per second. Then clamp the ends together and turn the crank again at the same
• In which case was the crank easier to turn? In which case did you do more work per second (remember that work is the product of force and distance)?
The crank was easier to turn when it was connected to the wood or plastic as opposed to when the ends were connected together. More work was required when the leads were connected together.
• If which case do you think more electrical current flowed through the wires attached to the generator?
More current flowed when the leads were attached together because more work was being done.
• How would you characterize the relationship between the current flowing and the difficulty of crank in the generator?
A direct relationship
• Does current flow more easily through the wires when they are attached to the wood or when they are clamped together?
Current flows more easily when the wires were clamped together.
• Would you say that the circuit resists the flow of electricity more with the wood between the clamps or when the clamps are directly attached to one another?
When the wood was between the clamps there was more resistance to flow
• In which case is there more electrical resistance, the case when the generator is easy to crank or when it is more difficult crank?
More electrical resistance when it is easy to crank.
Go around testing different objects in your house to see which ones have high resistance and which ones have low resistance to the flow of electrical current. Try to find at least three different materials that have low resistance and it least three to have high resistance.
High Resistance: Counter, computer desk, remote control
Low Resistance: Metal music stand, metal spoon, car keys
• Count the number of times you crank the generator in 10 seconds while the bulb glows, and record this data. Note also the numbers marked on the bulb, and record them.
24 revolutions – 148714V0.2A
• Repeat for the other bulbs in your kit. Some bulbs may require faster cranking than others. Some may crank at the same rate or easier. Find a way to mark the bulbs and record which is which.
18 revolutions - 6.3V0.15A 17 revolutions – 6.3V0.25A
Connect the leads of the generator so that current will flow through the first bulb but not the second. Describe how you made the connection.
Connected both leads to one holder, but not to the other.
• Crank the generator to make the bulb burn, and note how much force is required to crank the generator and how fast it has to be cranked.
20 revolutions in 10 seconds, moderately hard to crank.
Now connect the leads of the generator so that the current will flow first through the first bulb then through the wire lead connecting the two bulbs and finally through the second bulb and back to the generator. You will have a lead from the generator to the first bulb, another from the first bulb to the second and a third lead from the second bulb back to the generator.
• Crank the generator as before and note whether it requires more or less force to crank the generator, and whether the generator needs to be cranked faster or slower in order for the first bulb to burn as brightly as before.
Required faster cranking with less force.
• Do both bulbs burn with the same brightness? If not describe in terms of the previous observation of force and cranking rate the difference between the bulb that burns brighter and the bulb that burns more dimly.
The bulbs do not burn with equal brightness, the bulb burning brighter has less resistance.
• Crank the generator so that neither bulb burns too brightly and observe whether the generator requires more or less force to crank, compared to when the leads were attached to a single bulb. Note also whether the generator has to be cranked at the same rate, at a faster rate or at a slower rate in order for the first bulb to burn is brightly as before.
More force required and a faster crank rate to get the bulb to burn as brightly as before.
Answer the following questions:
• Which required more force to crank, the parallel or the series combination?
The Parallel circuit required more force to crank.
• Which required greater cranking speed to achieve the same bulb brightness, the parallel or the series combination?
The Series circuit required more speed to achieve the bulb brightness.
• Did both bulbs have the same relative brightness when they were connected in parallel as when they were connected in series?
Compared to each other the bulbs burned at the same brightness, however the bulbs were dimmer in the series circuit
• In which case do you think work was being done at the greater rate?
More work was being done for the Parallel circuit because it required more force, but in terms of rate they were probably close because the cranking was faster for the Series circuit.
It turns out that the amount of force necessary to turn the crank is an indication of the amount of electrical current flowing in the circuit, while the rate at which the crank is turned, in revolutions/second, is an indication of the amount of electrical 'push', or voltage, in the circuit.
More specifically:
• It is pretty much the case for this generator that the force F necessary to turn the crank is directly proportional to the current I flowing in the circuit: F = k1 * I, where k1 is a proportionality constant.
• It is also pretty much the case that the rate `omega at which the crank is turn is directly proportional to the voltage V pushing the current through the circuit: V = k2 * omega, where k2 is a proportionality constant.
In light of this information:
• Which circuit would you therefore say required the greater voltage, the series circuit or the parallel circuit?
The Series circuit required more voltage.
• Which circuit would you say required the greater current, the series circuit or the parallel circuit?
The Parallel circuit required more current.
Recall that power is the rate at which work is done: power = force * distance / `dt.
• As determined from the force necessary to crank the generator and from the rates at which the generator was cranked, which circuit seemed to require the greater power?
The series circuit was easier to crank, based on this it would seem to require more power because the cranking must be faster over time.
Faster cranking in one case, more force in the other. It would take either measurements of force and cranking rate, or an observation like the one you make below, to determine which requires more power.
• As determined from the brightness of the bulbs, which circuit seemed to require the greater power?
The parallel circuit burned dimmer and based on this would seem to require more power to achieve the same brightness.
Good.
_________________________________________________________________________
Experiment 17: Capacitors and Current, Voltage, Energy
The hand-cranked generator is connected to a large-capacity capacitor and the difficulty of cranking changes as time passes. This cranking difficulty vs. elapsed time is noted. The general nature of the current flow vs. time (i.e., increasing or decreasing) is inferred. The capacitor is connected in series and in parallel with a light bulb and the behavior of current vs. elapsed time inferred in each case; the effect of the light bulb is noted. The charged capacitor is allowed to discharge through the generator, then after recharging it is allowed to discharge through the light bulb; the nature of the capacitor is speculated upon.
Now connect the leads of the generator to the large capacitor, as shown on the video clip.
• Crank the handle of the generator at a constant rate of approximately two revolutions per second and keep cranking. After about a minute release the handle and see what happens.
• What happened to the amount of force necessary to crank the handle? What do you think was therefore happening to the amount of current flowing in the circuit?
The handle became easier to crank, so the amount of current was decreasing in the circuit.
• What happened after the handle was released and how could you possibly explain this?
The handle continued to turn after it was released, so some current was still being pushed through the circuit from the capacitor and caused the crank to continued to rotate.
• What evidence do you have that the capacitor in some way stored at least part of the energy you produced when you turned the crank?
The continued rotation of the crank is evidence that the energy produced was stored and then released.
This circuit is a series circuit consisting of the generator, the bulb and the capacitor.
• Crank the handle of the generator at a rate that causes the bulb to burn, but neither very brightly or very dimly. Continue cranking the handle at the same rate regardless of what happens. After about a minute, release the crank and see what happens.
• As you continue cranking, what do you notice about the force you have to exert, and what do you notice about the bulb?
As I continued to crank, it became easier to turn the generator and the bulb continued to decrease in brightness.
• After you stop cranking, what happens to the generator and what happens to the bulb?
After cranking stopped, the generator continued to turn and the bulb no longer burned.
• What happens to the voltage produced by the generator as you continue cranking?
The voltage, which I kept constant by turning the crank at the same rate, seemed to be maintained because there was still “push” when I stopped cranking.
• Does the voltage increase, decrease, or remain the same? How can you tell?
The voltage remained the same because the crank turned at roughly the same rate, which is proportional to the voltage.
• What happens to the current passing through the circuit as you continue cranking?
The current decreased as I continued cranking.
• Does the current increase, decrease, or remain the same? How could you tell if you weren't looking at the light? How can you tell by looking at the light?
The current decreases during the process. When not looking at the light I would know this because the crank became progressively easier to turn; if I were looking at the light I would know this because it gradually became dimmer.
• Sketch an approximate graph showing how the current through a capacitor behaves at a constant voltage.
An approximate graph of this would have a negative slope from high near time = 0 to low near time = 60 sec, because it begins at a higher current (harder to crank initially), and the current decreases over time because it becomes easier to crank while continuing to crank at roughly the same rate.
You have directly experienced the fact that the brightness of the light bulb depends on the voltage across the bulb (i.e., the faster you crank the generator when it is connected to a single bulb the brighter the bulb burns).
• What therefore do you conclude happens to the voltage across the bulb as you continue cranking the capacitor-and-bulb circuit?
The voltage is stored or maintained through the circuit because the generator continues to turn after it is released at close to the same rate initially that was being turned by hand.
• Based on the force required to crank the generator, what happens to the current through the light bulb? Is this consistent with your answer to the preceding question?
The current decreases which is consistent with the previous answer because if the voltage were in some way stored then the current would not be pushed through and the bulb would burn dimmer.
The total voltage across the capacitor and bulb remains constant as long as the generator is cranked a constant rate.
• Based on what you think happens to the voltage across the bulb as you continue cranking, what do you think happens to the voltage across the capacitor?
The voltage through the bulb was decreasing so the voltage across the capacitor must have been increasing since the crank was turned at a constant rate.