Video Transcript
The diagram shows a circuit
consisting of a cell, a resistor, a voltmeter, and an ammeter. The reading on the voltmeter is
three volts and the reading on the ammeter is 0.1 amperes. What is the resistance of the
resistor?
In this question, we see a diagram
of an electric circuit that has a cell providing a potential difference. We see that there is a resistor
connected in series with the cell, so the cell produces a potential difference
across the resistor. The potential difference across the
resistor produces a current in the resistor. There is actually a current in the
entire circuit, which is equal to the current in the resistor. We also see that an ammeter is
connected in series with the resistor and a voltmeter is connected in parallel with
the resistor. The ammeter is correctly connected
to measure the current in the circuit, and it reads 0.1 A, which stands for 0.1
amperes. The voltmeter is correctly
connected to measure the potential difference across the resistor, and it reads
three V, which stands for three volts.
Using the readings on the ammeter
and voltmeter, the resistance of the resistor can be determined. The resistance of the resistor can
be determined by applying Ohm’s law. Ohm’s law states that for two
points in a circuit, the potential difference across the points equals the current
between the points multiplied by the resistance of the object between the
points. Written as an equation, 𝑉 stands
for the potential difference across the resistor, 𝐼 stands for the current in the
resistor, and 𝑅 stands for the resistance of the resistor. To find the resistance, we must
make 𝑅 the subject of the equation. We can do this by dividing both
sides of the equation by current. This gives us the equation
resistance is equal to the potential difference divided by the current.
Let’s take a look at the units in
this equation before we begin putting in the given values and finding the
resistance. On the right-hand side, we have the
unit of volts divided by the unit amperes. On the left-hand side, we have the
unit of ohms, the unit of resistance. Now that we have this equation and
know the units for it, let’s substitute into the equation the values given by the
ammeter and voltmeter. The resistance of the resistor is
equal to three volts divided by 0.1 amperes. This gives us a value of 30 ohms
for the resistance of this resistor. This then is our answer to the
question.
