The purpose of this weeks’ hands on activity, was to have a better understanding on how to use the generator_lab.vi to measure the voltage output of a generator. In a thirty second time interval, our task was to correlate the number of shakes of the generator (in this case we used a flashlight), with the voltages (or more precisely the sum of the square of the voltages) that the generator generates. Furthermore, we performed four different experiments and recorded the data from the VI.
the 4 experiments consisted on:
- Shake the tube a different rates,
- Count the number of shakes in the data collecting interval (set to 30 seconds)
- Calculate in Excel the sum of the squares of the generated voltages (SSGV’s) (the voltage is logged after each second)
- Plot the SSGV’s as a function of # of shakes and fit the result to a linear curve
Before being able to compute our lab, we had a thoughtful lesson on Faraday’s law and how those the IV program works in relation to the data gathered by the generator and the voltage it outputs.
Faraday’s law is applicable to a closed circuit made of thin wire and states that:
The induced electromotive force (EMF) in any closed circuit is equal to the time rate of change of the magnetic flux through the circuit.
Or alternatively:
The EMF generated is proportional to the rate of change of the magnetic flux.
The law strictly holds only when the closed circuit is an infinitely thin wire; for example, a spinning homopolar generator has a constant magnetically induced EMF, but its magnetic flux does not rise perpetually higher and higher, as it would in a literal interpretation of the statements above.
So the “flux rule” that the emf in a circuit is equal to the rate of change of the magnetic flux through the circuit applies whether the flux changes because the field changes or because the circuit moves (or both)…. Yet in our explanation of the rule we have used two completely distinct laws for the two cases –
for “circuit moves” and
for “field changes”.
We know of no other place in physics where such a simple and accurate general principle requires for its real understanding an analysis in terms of two different phenomena.— Richard P. Feynman, The Feynman Lectures on Physics
Faraday’s Law states that changing magnetic fluxes through coiled wires generate electricity (currents and voltage). The greater is the change in magnetic flux, the greater are the currents and voltages. In this lab you will be shaking a tube which has a magnet that will travel back and forth through a coil of wires. You will show that the faster you shake the tube, the greater will be the generated voltage.
The image below clearly illustrates our gathered data, that was put in an excel spread sheet. Using that same data, we were able to plot the SSGV’s as a function of # of shakes and fit the result to a linear curve as seen below.
Work Cited
http://en.wikipedia.org/wiki/Faraday%27s_law_of_induction
