Video Transcript
The diagram below shows a design of
a generator. The generator consists of a coil of
wire wrapped around an iron core. Next to the coil is a bar magnet
attached to the end of a rod. When the rod spins, the bar magnet
spins, creating a changing magnetic field in the coil and iron core. How could the frequency of the
output potential difference be increased? (A) By removing the iron core. (B) By using a stronger magnet. (C) By spinning the magnet
faster. (D) By removing turns from the
coil. (E) By adding more turns to the
coil.
We’re being asked here about a
generator. Let’s begin by briefly recalling
that a generator like this uses electromagnetic induction to produce a current in a
conducting coil. As the magnetic field within the
coil changes, a changing potential difference is induced across the coil, producing
an alternating current. This is typically done by rotating
a coil in an unchanging magnetic field. But it can also be done in a
different way by rotating the magnet of the generator while keeping the coil
stationary. This is the case in this
question.
Here, we want to know how the
frequency of the output potential difference could be increased. The output potential difference is
proportional to the rate of change of the magnetic field experienced by the
coil. This means that the frequency of
the output potential difference depends on the frequency at which the magnetic field
that the coil is in changes. So in order to answer this
question, we have to recognize what would increase this frequency.
Let’s now consider the effect of
each suggested change given by the answer choices. Option (A) says to remove the iron
core. The purpose of the iron core is to
help maximize the generator’s efficiency and peak output potential difference by
shaping and strengthening the magnetic field. Removing the iron core would get
rid of these benefits while not affecting the frequency of the output potential
difference. Therefore, we can eliminate option
(A).
Next, option (B) says to use a
stronger magnet. Now this would increase the peak
potential difference across the coil, but it would not affect the frequency. So this answer choice is incorrect
as well.
Moving on, (C) says to spin the
magnet faster. Remember that the frequency at
which the magnet rotates corresponds to the frequency of the output potential
difference. So if we spin the magnet at an
increased frequency, we would in turn be increasing the frequency of the output
potential difference. Since this method would achieve
what we want here, then it looks like option (C) is the best choice. But let’s check out the remaining
options just to be sure.
Options (D) and (E) talk about
changing the number of turns in the coil. This would affect the peak
potential difference but not its frequency. So these answer options are both
incorrect.
Therefore, we know that the correct
answer is choice (C). The frequency of the generator’s
output potential difference could be increased by spinning the magnet faster.
