Video Transcript
Photovoltaic cells are often
used to power satellites. Which of the following are
reasons why photovoltaic cells are chosen as the power source for
satellites?
Now, before we read these
answer options, there are, even more than the four listed here. We’ll show those on the next
screen. But for reasons of space,
before we show them, let’s consider these four choices here.
The first possible reason says
that photovoltaic cells do not require a solid or liquid fuel that needs to be
resupplied in order to keep generating energy. Option B says that photovoltaic
cells require very little maintenance. Option C says that photovoltaic
cells provide direct current, which is what most electrical systems need to
work. And then option D says that
photovoltaic cells provide alternating current, which is what most electrical
systems need to work. Before we get on to options E
and F, Let’s evaluate these four.
So our situation is that
photovoltaic cells are being used as a power source on satellites. And the question is, which of
these reasons, if any, help explain why that is? To see which of these reasons
are legitimate, we can recall some of the advantages of photovoltaic cells. When we have such a cell, it’s
true that the only energy the cell requires is energy from the sunlight it
receives. There’s no need for any other
power supply or fuel source. This would come in very handy
in space on a satellite where power is hard to come by. All the photovoltaic cell needs
in order to keep generating electrical energy is sunlight or, specifically,
radiant energy. The source could be something
other than the Sun.
As we consider option A then,
we see that this option does describe a reason why such cells are used as a
power source for satellites. It’s true that they don’t
require any other power source in order to work. So we’ll highlight option A as
one of our answer choices.
On to option B, this says that
photovoltaic cells require very little maintenance. This also is true. Once a cell is set up and
working properly, not much is needed to keep it going. This, too, is an advantage in
space where repairs are not easy to make. So we’ll also choose option B
as a reason why photovoltaic cells are used as a power supply for
satellites.
Option C says that photovoltaic
cells provide direct current, which is what most electrical systems need to
work.
Now if we look ahead to option
D, we see that this says the same thing, except it claims that photovoltaic
cells produce alternating current. We can tell instantly that
options C and D can’t both be correct, since they claim opposite things about
the current generated by photovoltaic cells. If we were to connect a wire to
our photovoltaic cell and monitor the direction of the current, we would see
that as this cell works, as it converts radiant energy into electrical energy,
the current it produces is always running in the same direction. In other words, it’s generating
DC or direct current. It’s this type of current that
most electrical systems require in order to work. So we choose option C, which
describes the current produced by these cells this way. And we cross off option D. These cells produce direct
current but not alternating current.
Now we’re not done yet because
as we mentioned there are other possible answer options, options E and F, which
aren’t yet on the screen. Before we get to them, let’s
record these three answer options which we have identified as correct. Summarizing these choices, we
can say that option A indicates that no fuel is needed other than the
sunlight. Option B says that these cells
require very little maintenance. And option C says that they
output direct current, which is useful for most electrical systems.
Okay, now let’s clear some
space so we can write in options E and F and evaluate those. And here they are. Option E says photovoltaic
cells have always been very cheap to manufacture. And option F says that there
are no clouds in space to block the sunlight that the photovoltaic cells
need.
Looking at choice E, we can’t
say that this is an accurate statement. Even at their current state of
development, if someone wanted to put photovoltaic cells on their roof to
completely cover their energy needs, doing that would cost over 10,000
dollars. And this option is saying that
these cells have always been very cheap to manufacture. But surely in the very early
days of this technology, the costs were fairly high. So we won’t choose option E as
one of the reasons these cells are used as a power source for satellites.
This brings us to our last
option, option F, which says that there are no clouds in space to block the
sunlight that the photovoltaic cells need. And this indeed is an
outstanding reason why these cells are used as a power source for
satellites. The main disadvantages of
photovoltaic cells often come down to the fact that the sunlight on them isn’t
steady or reliable. But this is true only for cells
that are on the surface of the Earth, cells that sometimes face the Sun and
sometimes face away from it. And also the cells may have
clouds coming in between them and the Sun. But in space, outside of our
atmosphere, there are no clouds to interfere. This means that photovoltaic
cells are able to be more reliable power sources in satellites.
Altogether, we choose these
four answers. Photovoltaic cells need no
other fuel than sunlight to operate. They require little
maintenance. They generate direct current,
which many electrical systems require. And in space, there are no
obstructions between these cells and the Sun, no clouds or other atmospheric
conditions.