# 20 4 voltage current and resistance relationship

### Ohm's law - Wikipedia

Ohm's law states that the current through a conductor between two points is directly Ohm's law is an empirical relation which accurately describes the Francis Ronalds delineated “intensity” (voltage) and “quantity” (current) for the dry pile Ohm did his work on resistance in the years and , and published his. Ohm's law defines a linear relationship between the voltage and the current in Ohm's law formula; Ohm's law for AC circuit; Ohm's law calculator. Ohm's law formula. The resistor's current I in amps (A) is equal to the resistor's voltage V in volts of an AC circuit, that has voltage supply of V∟70° and load of kΩ∟ 20°. A graph of voltage against current is a straight line. The gradient is Ohm's Law can be rewritten in three ways for calculating current, resistance, and voltage. . such as T0 = K = 20°C at which the electrical resistivity ρ (T0) is known.

### Electrical/Electronic - Series Circuits

However the electrons collide with and scatter off of the atoms, which randomizes their motion, thus converting the kinetic energy added to the electron by the field to heat thermal energy.

Using statistical distributions, it can be shown that the average drift velocity of the electrons, and thus the current, is proportional to the electric field, and thus the voltage, over a wide range of voltages. The development of quantum mechanics in the s modified this picture somewhat, but in modern theories the average drift velocity of electrons can still be shown to be proportional to the electric field, thus deriving Ohm's law.

In Arnold Sommerfeld applied the quantum Fermi-Dirac distribution of electron energies to the Drude model, resulting in the free electron model. A year later, Felix Bloch showed that electrons move in waves Bloch waves through a solid crystal lattice, so scattering off the lattice atoms as postulated in the Drude model is not a major process; the electrons scatter off impurity atoms and defects in the material.

The final successor, the modern quantum band theory of solids, showed that the electrons in a solid cannot take on any energy as assumed in the Drude model but are restricted to energy bands, with gaps between them of energies that electrons are forbidden to have.

The size of the band gap is a characteristic of a particular substance which has a great deal to do with its electrical resistivity, explaining why some substances are electrical conductorssome semiconductorsand some insulators.

## Relationship and Difference Between Voltage, Current and Resistance

While the old term for electrical conductance, the mho the inverse of the resistance unit ohmis still used, a new name, the siemenswas adopted inhonoring Ernst Werner von Siemens. The siemens is preferred in formal papers.

In the s, it was discovered that the current through a practical resistor actually has statistical fluctuations, which depend on temperature, even when voltage and resistance are exactly constant; this fluctuation, now known as Johnson—Nyquist noiseis due to the discrete nature of charge.

Ohm's work long preceded Maxwell's equations and any understanding of frequency-dependent effects in AC circuits. Modern developments in electromagnetic theory and circuit theory do not contradict Ohm's law when they are evaluated within the appropriate limits.

Scope Ohm's law is an empirical lawa generalization from many experiments that have shown that current is approximately proportional to electric field for most materials. It is less fundamental than Maxwell's equations and is not always obeyed. These all are operated using the basic power source that is, the movement of electrons. Current is the flow of electrons Resistance is defined as, it is the tendency of a material to restrict the flow of current.

So, when we discuss about these values, the behavior of electrons in a closed loop circuit allows charge to move from one place to another.

He described a unit of resistance which is defined by voltage and current.

The difference between voltage and current and resistance is discussed below. In this equation, voltage is equal to the current and that is multiplied by resistance.

Basic Circuit Diagram of V, I and R In the above circuit, when the voltage and resistance values are given, then we can calculate the amount of current. The differences between V, I and R are discussed below. The voltage is defined as, it is the potential difference in charge between the two points on a circuit, it is also called electromotive force. One point has more charge than another.

The unit volt is termed after invented by Italian physicist Alessandro Volta. The term volt is represented by the letter V in schematics. The measuring instrument of voltage is the voltmeter. Voltage is the source and the current is its result, it can occur without current.

The voltage gets distributed over different electronic components which are connected in series in the circuit, and in parallel circuit voltage is same across all components which are connected in parallel.

It's not some kind of absolute number. It's a difference between essentially how bad do electrons want to get from here to here. So if we measure the voltage between those two points, it would be the exact same thing as if we measured the voltage between these two points.

### Relationship and Difference Between Voltage, Current and Resistance

As we know, no wires really have no resistivity. All wires have a little bit, but when we draw these schematics, we assume that the wires are perfect conductors and all the resistance takes place in the resistor. So that's the first thing I want you to realize, and it makes things very-- so, for example, everywhere along this wire, this part of the wire, the voltage is constant.

Everywhere along this wire, the voltage is constant. Let me erase some of this, because I don't want this to get too messy.

## Ag Power Web Enhanced Course Materials

That's a big important realization when you later become an electrical engineer and have much harder problems to solve. Let me erase all of this. Let me erase all of that. Let me redraw that, because we can't have that gap there, because if there was that gap, current wouldn't flow.

That's actually-- well, I'll draw later how you can draw a switch, but a switch is essentially a gap. It looks like a gap in the circuit that you can open or close, right? Because if you open it, no current will flow. If you close it, current will flow. OK, so you now know that the voltage between devices is constant. The other thing I want to convince you is that the current through this entire circuit is constant, and that applies to any circuit in series. Now, what do I mean by series?

Series just means that everything in the circuit is after one another, right? If we take the convention and we say current flows in this direction, it'll hit this resistor, then the next resistor, then the next resistor. At no point does the circuit branch off and have to choose whether I want to go down path A or path B.

**Basic Electricity - Resistance and Ohm's law**

So this circuit is completely in series, and there's a couple ways I can convince you that the current-- let's call the current here I1. Let's call this current here I2. Let's call this current here I3. I could draw another one here, I3. So there's a couple of ways I can convince you that I1 equals I2, I3. One is I could just say if you experimentally tried it out using an ammeter, which measures current, you would see that they are identical. But the other way to think about it, and this time I'm going to actually talk about the electrons, so let's talk about things going in this direction, is-- so these electrons, through this wire, they can go as fast as they want to go, right?

The speed of light or close to the speed of light since they have very, very, very low mass. And we'll go into relativity one day. But once they get to this resistor, they start bumping into things, and they slow down. This resistor is a bit of a bottleneck, right?

So as fast as they're traveling here, they have to slow down here. And if they slow down here, they have to slow down here, because if they kept going superfast here and then they slowed down here, then they would start building up here, and that just doesn't make sense, because we know that they're evenly spread out, et cetera.

And similarly, they might exit this resistor at a certain speed and then slow down even further as they bump into resistors here, but if they're going even slower at this point, then there would be a bottleneck here, so essentially, they would have to go at that rate throughout the whole thing. And another way to think about it is the resistance is kind of a probabilistic thing.

I know when you think on a macro level, you say, oh, it has this resistance. It just slows it down.