A rectified current generator uses multiple current loops offset at different angles
from their common axis of rotation. The generator can use either four loops or five loops. The output from the generator and from each loop individually using four loops is
shown in black, and the equivalent output using five loops is shown in red. What is an advantage of using the five-loop arrangement over the four-loop
arrangement? (A) The current is less variable. (B) The mean current is greater.
In this question, we are told that a rectified current generator uses multiple
current loops offset at different angles from their common axis of rotation. And they can use either four loops or five loops. We are given a time-and-current graph that shows us the output from the generator and
from each loop for both the four-loop and five-loop arrangement. It has the output for the four-loop arrangement in black and the five-loop
arrangement in red. We are asked to look at this graph and figure out what the advantage to using a
five-loop arrangement would be over the four-loop arrangement. Let’s remind ourselves what a rectified current generator is and then take a look at
this graph and see what we can figure out.
A generator is a device that transfers mechanical energy into electrical energy. It does this by applying a mechanical force and rotating a coil of wire that is held
inside a uniform magnetic field. As the coil rotates in the magnetic field, a current is induced in the coil.
Now, this question is asking us about a generator using four loops or five loops in
its coil and how that would change the current generated. Since an electric current is induced in a loop rotating in a magnetic field, if we
had more loops in a coil, we would expect that there would be more current
generated. Let’s look at the graph given and see if we can see that there.
Let’s take a look at the line representing the four-loop arrangement, the black solid
line. We can find the mean current of the four-loop arrangement by adding together the
amplitude of the current at each time and dividing that sum by the total time we
consider. This is shown as the dotted straight black line. Similarly, we can look at the lines representing the five-loop arrangement, the
dotted red lines, and see its mean as the straight dotted red line.
Notice that the mean current for the four-loop arrangement has a lower value of
current than the five-loop arrangement. This means that the five-loop arrangement has a mean current that is greater than the
four-loop arrangement. So option (B), the mean current is greater, is the correct answer.