Video Transcript
The diagram shows an electric
circuit containing a cell and a bulb. The current in the circuit is two
amperes. How much charge flows past point 𝑃
in the circuit in one second? The current in the circuit is two
amperes. How much charge flows past point 𝑃
in the circuit in one second?
The diagram shows the cell, the
bulb, and also the wires connecting these two components. The point 𝑃 is over here, and the
arrow shows us the direction of the current. And we are told that the value of
this current is two amperes. Recall that the unit symbol for the
ampere is the uppercase letter A. Now, the question asks us to
determine how much charge flows past point 𝑃 in the circuit in one second if the
current in the circuit is two amperes. To do this, we’ll need to recall
how current is related to charge and time. One ampere, the unit for current,
is defined as one coulomb of charge moving past a point in one second.
In our question, we’re also
interested in a time of one second. But instead of a current of a
single ampere, we have a current of two amperes. Luckily, the conversion is
easy. If one ampere is one coulomb per
second, then two amperes is two coulombs per second. And this is our answer. Two amperes is two coulombs of
charge passing a point every one second. So the answer is two coulombs.
We should pay careful attention to
the two statements we’ve written down. On the left, we defined one ampere
with a time of one second and two amperes also with a time of one second. This is because current is always
defined by how much charge moves past a point in exactly one second. So as the current changes, the
amount of charge changes, but not the amount of time it takes that charge to
move.
