• Astrophysics • Electricity • Electromagnetism • Energy • Fields • Force • Mechanics • Momentum • Nuclear Physics • Quantities & Units  • States of Matter • Waves • Key Experiments Ohm's Law was discovered by a German physicist Simon Ohm in 1827. He did experiments on simple electrical circuits with wire of different lengths. Ohm's Law is one of the most important principles of electrical circuits. It says that the voltage across two points in an electric circuit is directly related to the current passing between those two points. This relation is proportional to resistance. The formula for Ohm's Law is V = IR. Here, V is the voltage across a conductor, I is the current passing through the conductor, and R is the electrical resistance of the conductor. The resistance in Ohm's Law is always constant and can be calculated by taking a series of voltage and current measurements over a range of values before plotting the data on a straight-line graph and finding its gradient. Before we continue explaining Ohm's Law, let's review some basic concepts around electric circuits. Remember, understanding Ohm's Law is fundamental to understanding how electricity works!

## Ohm's Law: Electric circuits

Electric circuits are made up of electrical components connected by wires, allowing electric current to flow through them. Electric current is made up of moving electrons that move around the wire due to an applied voltage. In order for components to allow the flow of electric charge, they must be made of electrically conductive materials, such as metals which are good conductors of electricity.

When studying electric circuits, we differentiate between Ohmic conductors and non-Ohmic conductors. Ohmic conductors follow Ohm's law, meaning the voltage vs current graph has a linear relationship. Copper, which is highly conductive, is an example of an Ohmic conductor. Non-Ohmic conductors, on the other hand, do not follow Ohm's law and have a non-linear relationship between voltage and current. Understanding the difference between these types of conductors is essential to understanding electric circuits and how they work.

Non-Ohmic conductors do not follow Ohm's law and have a non-linear relationship between current. Examples of non-Ohmic conductors include bulb filaments and some semiconductors like transistors or di.

On the other hand, insulators are materials that do not conduct electricity well. They can be used to slow or stop the flow of electric charge and have various applications in the real world. For, the plastic covering of electrical wires acts as an insulator and prevents electric shocks.

### Ohm's Law: Voltage

Voltage, also known as potential difference, is the difference in electric potential between two points in a conductor. It is measured in volts (V), which is the standard unit for potential difference.

In an electric circuit, voltage is generated by a cell or battery. A cell or battery has a positive terminal with a higher potential and a negative terminal with a lower potential. This difference in potential creates an electric field that drives the flow of electric charge through the circuit.

Understanding voltage and how it is generated is crucial in designing and analyzing electric circuits, as it determines the direction and magnitude of electric current flowing through the circuit.

### Ohm's Law: Current

Current is the rate of flow of electric charge. The device that we use to measure current in an electric circuit is called an ammeter. The standard unit for electrical current is the Ampere (A).

### Ohm's Law: Resistance

Resistance is a measure of how much a conductor resists the flow of electric current. It is measured in Ohms (Ω), which is the standard unit for resistance. The resistance of a conductor increases with length and decreases with thickness, and it also depends on the material it is made from.

For example, copper wire is a better conductor of electricity than aluminium wire because it has a lower resistance. However, if the aluminium wire is four times as long as the copper wire, it will have a higher resistance.

To increase the resistance of an electric circuit, we can add a component called a resistor. A resistor is a fixed component that obeys Ohm's law and has a specific, fixed resistance value. Different resistors are used for different purposes in electrical circuits, such as regulating current or voltage.

## The derivation of Ohm’s law

It is true that there is no exact derivation for the formula of Ohm’s law. As mentioned earlier, the law was stated in 1827 by Georg Simon Ohm, but it is an empirical law, which means that it was originally based on observations rather than derived from first principles. Ohm discovered the law by observing the behaviour of Ohmic conductors whilst applying a current to them. Based on the data obtained, Ohm stated that there was a linear relationship between the current and the intensity, but he did not derive the law theoretically.

However, since then, physicists have attempted to derive the law from first principles. For example, Khan Academy provides a derivation of Ohm's law using the expression for drift velocity, electric current (in terms of drift velocity), and connection between electric field and potential. Similarly, Winner Science provides a derivation of Ohm's law using the concept of mobility of the electron. Lastly, Physics Stack Exchangeprovides a derivation of Ohm's law using linear response theory.

## The formula for Ohm’s law revisited

Yes, that's correct. Ohm's law states that the voltage across a conductor is directly proportional to the current passing through it, which can be expressed as V = IR. This means that if we increase the current passing through a conductor by a certain factor, the voltage will increase by the same factor and vice versa.

We can rearrange the formula to solve for different variables. For example, if we know the current and voltage, we can calculate the resistance using the formula R = V/I. Similarly, if we know the voltage and resistance, we can calculate the current using the formula I = V/R.

To summarize, if we know any two of the variables in Ohm's law (voltage, current, and resistance), we can calculate the third. This allows us to analyze and design electric circuits, and to understand the behavior of electrical components such as resistors, capacitors, and inductors.

This triangle is called the Ohm’s law triangle. To remind ourselves of how to calculate each of V, I, and R, we set up the triangle, with V in the top segment and I and R in the bottom segments. To calculate the value of either of the variables at the bottom of the triangle, we simply divide the value of V by the value of the other remaining variable in the bottom part of the triangle. V is simply calculated by multiplying the values of the two variables in the bottom segment of the triangle, namely I and R.

If you struggle to rearrange equations, you may prefer to calculate V, I, and R using the Ohm’s law triangle. Just remember to draw a triangle and separate it into three

A 9 V battery produces a current of 3 A in a wire. What is the resistance of the wire?

To solve this problem, we use Ohm’s law. Using our knowledge of rearranging equations or the Ohm’s law triangle, we find that the formula to compute the resistance is: To find either of the two variables in the bottom level of the Ohm’s law triangle, we divide the voltage by the other variable in the bottom level. In this case, we divide V by I to find R. Therefore, the resistance of the wire in this example is:

Determine the voltage of an electric circuit with a current of 0.5 A and a resistance of 20 Ω.

In this case, we need to use the first form of Ohm’s law. We find the formula of Ohm’s law for the voltage using the Ohm’s law triangle:

Now, we can introduce the data for the electric circuit provided in the question by substituting 0.5 A for the current and 20 Ω for the resistance:

Given the following electric circuit, calculate the current passing through it once the switch is closed.

As we can see in the figure above, the electric circuit has a potential difference of 30 V across its terminals, and the resistor has a resistance of 10 Ω. We have to rearrange the original form of the Ohm’s law formula. If we take a look at the Ohm’s law triangle, we can rearrange the formula to calculate the current:

Using the values of the variables provided in the figure, we can calculate the current as follows:

Ohm’s Law - Key takeaways Ohm’s law states that the voltage or potential difference V across two points in an electric circuit is proportional to the current passing through it, and the constant of proportionality is the resistance. The general expression for Ohm’s law is V = IR. An electric circuit is a set of electrical components connected with wires through which an electric charge flows. It consists of elements made of conductive materials that allow the electric charges to move along them. Materials that do not conduct electricity well are called insulators. Voltage is the difference in electric potential between two points. The standard unit of voltage is the volt (V).Current is the rate of flow of electric charge. The standard unit of current is the ampere (A).Resistance is the property of a conductor that resists the flow of electric charge. The standard unit for resistance is the Ohm (Ω).Ohm’s law can be used to calculate voltage, resistance, and the current of electric conductors, provided the other two variables are known. One way to remember the Ohm’s law formula is the Ohm’s law triangle.

## Ohm's Law

What is Ohm’s Law?

Ohm’s law is a law stated by Georg Simon Ohm that relates the voltage across a conductor to the current passing through it and its electrical resistance. It states that the voltage across two points in an electric circuit is directly proportional to the current passing through it, and the constant of proportionality is the resistance.The equation for Ohm’s Law is: V = I RHere, V is the voltage between two points in a conductor, I is the current passing through the conductor, and R is the resistance of the conductor.

What are the three formulas in Ohm’s law?

The first formula for Ohm’s law is: V = I RDepending on what we want to calculate, we can rearrange this formula. If, for example, we want to compute the resistance, we have:   R = V/IFor the current, we get:  I = V/R

What does Ohm’s Law state?

Ohm’s law states that the voltage or potential difference across two points in an electric circuit is directly proportional to the current passing through it, and the constant of proportionality is the resistance.The formula for Ohm’s law is:   V = I R Here, V is the voltage, I is the current, and R is the resistance.

What is the equation for Ohm’s Law?

The equation for Ohm’s Law is:   V = I RHere, V is the voltage between two points in a conductor, I is the current passing through the conductor, and R is the resistance of the conductor.

How do you find the resistance in Ohm’s law?

You need to apply the Ohm’s law formula:  R = V/IHere, V is the Voltage across two points in a conductor, R is the resistance of the conductor, and I is the current. 14-day free trial. Cancel anytime.    Join 10,000+ learners worldwide. The first 14 days are on us 96% of learners report x2 faster learning Free hands-on onboarding & support Cancel Anytime