Video Transcript
Which of the following is the unit
of electric charge? (A) The newton, (B) the ampere, (C)
the coulomb, (D) the watt, (E) the joule.
It’s good to remember that units
are an important part of science because they tell us the exact type of quantity
we’re working with. They can even help give us clues
about how to answer a question, so long as we can recall which units measure which
types of things.
This question is asking for the
unit of electric charge. When we talk about electric charge,
we might remember that certain particles in an atom, such as protons and electrons,
have charge. So, say we want to measure the
charge of one proton. Which unit do we need to use in
order to do so?
Option (A) says the newton, and we
can recall that newtons help us describe force. For instance, we might say that a
book exerts a force of 20 newtons downward while resting on a table. So, the newton helps us measure
force, but not electric charge. Let’s eliminate this answer
choice.
Next, (B) says the ampere. When we think of amperes, we might
think of electricity, because the ampere measures electric current. Electric current is related to
electric charge, but they are not the same thing. Electric current is actually the
rate of flow of charge past a certain point in an electric circuit. So, we cannot measure electric
charge using the ampere. Therefore, answer choice (B) is
wrong as well.
Moving on, option (C) says the
coulomb, which is exactly the unit we’re looking for. A proton has a very small charge of
1.6 times 10 to the power of negative 19 coulombs. So, answer choice (C) seems to be
the best option. Just to be sure though, let’s have
a look at the remaining two choices.
Option (D) says the watt, which
might make us think of light bulbs, because they are often marketed by their power
rating. And the watt is the unit of
power. Therefore, we know that the watt
isn’t the unit of electric charge. The last choice (E) says the joule,
a unit that measures work and energy. So, again, this is not the unit we
are looking for.
We’ve seen that the correct answer
is (C), and we’ve ruled out all other answer options. The coulomb is the unit of electric
charge.
