# Unit of resistance and current relationship

### Ohm’s Law - How Voltage, Current, and Resistance Relate | Ohm's Law | Electronics Textbook So to display the units or multiples of units for either Resistance, Current or unit which is mainly used in a.c. circuits to represent the Phasor Relationship. The first, and perhaps most important, relationship between current, voltage, and standard units of measurement for electrical current, voltage, and resistance. The ohm (symbol: Ω) is the SI derived unit of electrical resistance, named after German . Since so-called "absolute" units of charge and current are expressed as of the relations between potential, current, and resistance show that resistance.

So let's say I have this vertical pipe of water, it's closed at the bottom right now, and it's all full of water. There's water above here as well. So the water in the pipe, so let's say the water right over here, it's gonna have some potential energy.

### Introduction to circuits and Ohm's law (video) | Khan Academy

And this potential energy, as we will see, it is analogous to voltage. Voltage is electric potential, electric potential. Now it isn't straight up potential energy, it's actually potential energy per unit charge. So let me write that. Potential energy per unit, unit charge. You could think of it as joules, which is potential energy, or units of energy per coulomb. That is our unit charge. And the units for voltage in general is volts.

Now, let's think about what would happen if we now open the bottom of this pipe. So we open this up. Well, the water's immediately gonna drop straight down. That potential energy is gonna be converted to kinetic energy. And you could look at a certain part of the pipe right over here, right over here. And you could say, well, how much water is flowing per unit time? And that amount of water that is flowing through the pipe at that point in a specific amount of time, that is analogous to current.

Ohms Law Simplified

Current is the amount of charge, so we could say charge per unit time. Q for charge, and t for time. And intuitively you could say, how much, how much charge flowing, flowing past a point in a circuit, a point in circuit in a, let's say, unit of time, we could think of it as a second. And so you could also think about it as coulombs per second, charge per unit time. And the idea of resistance is something could just keep that charge from flowing at an arbitrarily high rate. And if we want to go back to our water metaphor, what we could do is, we could introduce something that would impede the water, and that could be a narrowing of the pipe.

And that narrowing of the pipe would be analogous to resistance. So in this situation, once again, I have my vertical water pipe, I have opened it up, and you still would have that potential energy, which is analogous to voltage, and it would be converted to kinetic energy, and you would have a flow of water through that pipe, but now at every point in this pipe, the amount of water that's flowing past at a given moment of time is gonna be lower, because you have literally this bottleneck right over here. So this narrowing is analogous to resistance. How much charge flow impeded, impeded. And the unit here is the ohm, is the ohm, which is denoted with the Greek letter omega.

## GCSE Science/Current, voltage resistance and Ohm's law

In Werner Siemens — published a suggestion for a reproducible resistance standard in Poggendorffs Annalen der Physik und Chemie. However, this unit was not coherent with other units. One proposal was to devise a unit based on a mercury column that would be coherent — in effect, adjusting the length to make the resistance one ohm. Not all users of units had the resources to carry out metrology experiments to the required precision, so working standards notionally based on the physical definition were required.

InLatimer Clark — and Sir Charles Bright — presented a paper at the British Association for the Advancement of Science meeting  suggesting that standards for electrical units be established and suggesting names for these units derived from eminent philosophers, 'Ohma', 'Farad' and 'Volt'. The error was significant for preparation of working standards. Although called "legal", this standard was not adopted by any national legislation.

The "international" ohm was recommended by unanimous resolution at the International Electrical Congress in Chicago. The International Ohm is represented by the resistance offered to an unvarying electric current in a mercury column of constant cross-sectional area Inthis definition was adopted by scientific representatives from several countries at the International Conference on Electric Units and Standards in London. But there may be an equally large water pressure below the pipe, which tries to push water back up through the pipe.

If these pressures are equal, no water flows. In the image at right, the water pressure below the pipe is zero. The resistance and conductance of a wire, resistor, or other element is mostly determined by two properties: In the same way, a long, thin copper wire has higher resistance lower conductance than a short, thick copper wire.

Materials are important as well. A pipe filled with hair restricts the flow of water more than a clean pipe of the same shape and size.

## Ohm’s Law - How Voltage, Current, and Resistance Relate

Similarly, electrons can flow freely and easily through a copper wire, but cannot flow as easily through a steel wire of the same shape and size, and they essentially cannot flow at all through an insulator like rubberregardless of its shape.

The difference between copper, steel, and rubber is related to their microscopic structure and electron configurationand is quantified by a property called resistivity. In addition to geometry and material, there are various other factors that influence resistance and conductance, such as temperature; see below. Conductors and resistors[ edit ] A 6. An ohmmeter could be used to verify this value. Substances in which electricity can flow are called conductors. A piece of conducting material of a particular resistance meant for use in a circuit is called a resistor.

Conductors are made of high- conductivity materials such as metals, in particular copper and aluminium. Resistors, on the other hand, are made of a wide variety of materials depending on factors such as the desired resistance, amount of energy that it needs to dissipate, precision, and costs.