course phy
Good work. Very good answers to questions.
Let me know if anything is unclear, and include specifics about what you do and do not understand.
Experiment 16: Current Flow and EnergyClamp 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 leads were connected together, so there was more work 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 and more work was being done.
?How would you characterize the relationship between the current flowing and the difficulty of crank in the generator?
The more difficult it is to crank the more current is flowing, so 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?
More resistance to flow when the wood was between the clamps
?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? 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 top, computer desk, remote control
Low Resistance: Oven handle, 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 then when it was and a faster 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 samerelative brightness when they were connected in parallel as when they were connected in series?
In terms of the relationship of one burning brighter than the other, yes that was the case in both examples, but 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 because of the higher rate of turning required.
?Which circuit would you say required the greater current, the series circuit or the parallel circuit?
The Parallel circuit required more current because it was more difficult to crank.
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.
?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.
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