Video Transcript
David sets up three circuits. He measures how much charge flows
through each circuit in the same amount of time. His results are shown in the
following table. Which circuit has the greatest
current?
We need to determine which of
circuits one, two, and three has the greatest current based on the information in
this table. To practice calculating the current
in a circuit, we will calculate the current in each circuit from the charge and time
in the table and then compare those results. Recall that we can calculate
current from the equation 𝐼 equals 𝑄 divided by 𝑡, where 𝐼 is the current
measured in amperes, 𝑄 is the charge measured in coulombs, and 𝑡 is the time
measured in seconds. All we need to do now is substitute
the values from each circuit into this equation.
In circuit number one, the charge
is 20 coulombs and the time is five seconds. So using 𝐼 equals 𝑄 divided by
𝑡, we have 20 divided by five, which is four. And since our units for charge are
coulombs and our units for time are seconds, the units for this current are coulombs
per second, or amperes. So the current in circuit one is
four amperes. In circuit number two, the charge
is 25 coulombs and the time is five seconds. Since the units for charge and time
are again coulombs and seconds, the current will again have units of amperes, and
its numerical value will be 25 divided by five. 25 divided by five is just
five. So the current in the second
circuit is five amperes.
Finally, in the third circuit, the
charge is 12 coulombs and the time is again five seconds. The units for charge and time are
again coulombs and seconds, so the units for the current will again be amperes. And the numerical value will this
time be 12 divided by five. Since 12 divided by five is 2.4,
the current in the third circuit is 2.4 amperes. Now that we have calculated the
current in each circuit, we can see immediately that the greatest current is five
amperes in circuit two. So the circuit with the greatest
current is circuit two.
