### Video Transcript

Which of the following is equal to
one nanowatt when multiplied by one watt? A) 10 to the power of nine, B) 10
to the power of negative eight, C) 10 to the power of negative nine, D) 10 to the
power of six, E) 10 to the power of negative six.

Okay, so this question is worded in
a bit of a confusing way. Essentially, what it’s asking us is
which one of these options — so let’s say one of these options will be filled out in
this blank here — is equal to one nanowatt, which we can write as one lower case n
capital W, when multiplied by one watt. In other words, we have to stick
one of the options A to E in this blank here, and when we multiply that option by
one watt, we get one nanowatt.

So, let’s start by recalling that
the watt is a unit of power, and nano is a prefix. Specifically, it’s one of the SI
prefixes used to represent either a large multiple or a small fraction of the unit
that we’re using, in this case the watt. More specifically, we can recall
that one nanowatt, abbreviated nW, is equal to 10 to the power of negative nine
watts.

And therefore, looking at the
options A to E that we’ve been given, we can see that if we stick 10 to the power of
negative nine into our blank here, then what we’d get is 10 to the power of negative
nine multiplied by one watt is equal to one nanowatt. Which we’ve already seen is
equivalent to 10 to the power of negative nine watts. And 10 to the power of negative
nine multiplied by one is indeed equivalent to 10 to the power of negative nine. Therefore, we’ve got the exact same
thing on the left-hand side and on the right-hand side. In other words then, the answer
that we’re looking for is option C. 10 to the power of negative nine
multiplied by one watt is equivalent to one nanowatt.