Question Video: Using Ohm’s Law to Find the Resistance of a Resistor | Nagwa Question Video: Using Ohm’s Law to Find the Resistance of a Resistor | Nagwa

# Question Video: Using Ohm’s Law to Find the Resistance of a Resistor Physics • Third Year of Secondary School

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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 A. She then uses a voltmeter to measure the potential difference across the resistor and gets a value of 10 V. What is the value of the resistance of the resistor?

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### 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.

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