# Question Video: Using the Readings from a Voltmeter and an Ammeter to Calculate the Current through a Resistor Science

The diagram shows a circuit consisting of a cell, a resistor, a voltmeter, and an ammeter. The reading on the voltmeter is 3 volts and the reading on the ammeter is 0.1 amperes. What is the resistance of the resistor?

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### 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.