### Video Transcript

A student sets up the circuit shown
in the diagram. She uses an ammeter to measure the
current through the circuit and gets a value of 2.5 amperes. She then uses a voltmeter to
measure the potential difference across the resistor and gets a value of 10
volts. What is the value of the resistance
of the resistor?

In this question, we are given a
circuit consisting of a cell and a resistor. 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.

The ammeter is used to measure the
current in the circuit, and it gives a value of 2.5 A, which stands for 2.5
amperes. The voltmeter is used to measure
the potential difference across the resistor, and it gives a value of 10 V, which
stands for 10 volts. Using the readings on the ammeter
and voltmeter, the resistance of the resistor can be determined using Ohm’s law.

Recall that Ohm’s law states 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. Ohm’s law can be written as an
equation, where 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 the current. This gives us the equation
resistance 𝑅 is equal to the potential difference divided by the current.

Before putting in the given values,
it’s always a good idea to take a look at the units we are working with. In this equation, we have the unit
of volts divided by the unit of amperes on the right-hand side, and that is equal to
the unit of ohms on the left-hand side. Now, let’s go ahead and put in the
given values and solve this equation. The resistance of the resistor is
equal to 10 volts divided by 2.5 amperes, which is equal to four ohms.

So our final answer is the
resistance of the resistor 𝑅 equals four ohms.