Using Ohm's Law
Using Ohm's Law
We are now ready to see how Ohm's Law is used to analyze circuits.
Consider a circuit with a cell and an ohmic resistor, R. If the resistor has a resistance of \(\text{5}\) \(\text{Ω}\) and voltage across the resistor is \(\text{5}\) \(\text{V}\), then we can use Ohm's Law to calculate the current flowing through the resistor. Our first task is to draw the circuit diagram. When solving any problem with electric circuits it is very important to make a diagram of the circuit before doing any calculations. The circuit diagram for this problem looks like the following:
The equation for Ohm's Law is: \[R = \frac{V}{I}\]
which can be rearranged to: \[I = \frac{V}{R}\]
The current flowing through the resistor is:
\begin{align*} I &= \frac{V}{R} \\ &= \frac{\text{5}\text{ V}}{\text{5}\Omega} \\ &= \text{1}\text{ A} \end{align*}
Example: Ohm's Law
Question
Study the circuit diagram below:
The resistance of the resistor is \(\text{10}\) \(\text{Ω}\) and the current going through the resistor is \(\text{4}\) \(\text{A}\). What is the potential difference (voltage) across the resistor?
Step 1: Determine how to approach the problem
We are given the resistance of the resistor and the current passing through it and are asked to calculate the voltage across it. We can apply Ohm's Law to this problem using: \[R = \frac{V}{I}.\]
Step 2: Solve the problem
Rearrange the equation above and substitute the known values for \(R\) and \(I\) to solve for \(V\). \begin{align*} R &= \frac{V}{I} \\ R \times I&= \frac{V}{I} \times I\\ V &= I \times R \\ &= \text{10} \times \text{4} \\ &= \text{40}\text{ V} \end{align*}
Step 3: Write the final answer
The voltage across the resistor is \(\text{40}\) \(\text{V}\).
This lesson is part of:
Electric Circuits