GCSE Science/Current, voltage resistance and Ohm's law - Wikibooks, open books for an open world
Electronics Tutorial about the Relationship between Voltage Current and The Potential difference between two points is measured in Volts with the . The standard unit of measurement given for conductance is the Siemen, symbol (S). Current Electricity - Lesson 1 - Electric Potential Difference Because electric potential difference is expressed in units of volts, it is sometimes referred to as the .. of the mathematical relationship between work, potential energy, charge and . Charge, Current & Potential Difference in circuits. Conventional current flows around a circuit from the positive (+) side of the cell to the negative (-). Potential difference is the work done per unit charge. Resistance (W) – is the ratio of potential difference across a component to the current flowing through it, it is.
Electrons are flowing past you. One Ampere is a flow of one coulomb going past every second. The ampere is defined in terms of the force produced between two wires each carrying identical currents: Voltage[ edit ] Having looked at charge and current, we now need to look at what voltage means.
As you know, electrons repel each other. If you hold one electron near another electron, you have to push against it to hold it in place. If you try to bring it even closer, you have to do work force times distance to get it to that new position.
The voltage between one point and another is simply how much work per coulomb is required to move any small test charge from point A to point B. In most electronic components, it doesn't matter much which path the test charge takes in-between point A and point B. Voltage is related to the energy of the charges.
Let's go back to the peas in the petri dish. They can be pushed slowly or they can be pushed quickly. The faster they go, the more energy they have. It's a similar situation for the electrons, except the push isn't provided by a finger! It's provided by the battery. The battery gives the charges energy. This energy is given up to the various components in the circuit, e. The energy per unit charge is called the voltage or the potential difference.
Definition of the volt[ edit ] One volt means one joule of energy per coulomb of charge. More accurately it has 2 definitions: Electromotive Force is the amount of energy converted from non-electrical to electrical form when driving 1 coulomb of charge around a completed and closed circuit. Potential Difference is the amount of energy converted from electrical to non-electrical form when driving 1 coulomb of charge around a completed and closed circuit.
The potential difference between 2 points in a conductor is defined as 1 volt, if 1 Joule of energy is converted from electrical form to non-electrical form, when 1 coulomb of charge per second 1 amp flows through it. This will only occur between 2 points in a conductor, that has a resistance, defined as 1 ohm. It's just how difficult it is for the charges to flow through an electrical component or from one point to another in an electrical circuit.
Imagine a group of walkers travelling down a road.
They approach a fork in the road. To the left is a flat straight road leading to a nearby town. To the right is a huge mountain, over which a steep and winding road traverses.
This road also leads to the nearby town.
Naturally all the walkers chose the left route. Let's now suppose that there are millions of walkers. They are jam packed on the road, and they are all in a hurry to get to the town as quickly as possible.
Now when they come to the fork in the road which way should they go? Most will still go to the left, but a few might chose to go to the right, the road is more difficult but there is no traffic jam, so they might get there quicker.
It's a similar thing with moving charges. Like charges repel, so they would rather not pack in very closely together. Some routes, like wires have very low resistance, while other routes like bulbs have much higher resistance. More charges will go down a low resistance route than a high resistance one. Ohm's Law[ edit ] This law relates resistance, current, and voltage.
It's very easy to remember because it's obvious when you think about it. Let's think of a wire carrying current from a battery, to a bulb then back to the battery. The voltage of the battery provides the energy of the flowing electrons. Let's assume we want to increase the rate of flow of charge. Remember that current is the rate of flow of charge so we want to increase the current.
In the previous part of Lesson 1, the concept of electric potential was applied to a simple battery-powered electric circuit. In that discussionit was explained that work must be done on a positive test charge to move it through the cells from the negative terminal to the positive terminal.
This work would increase the potential energy of the charge and thus increase its electric potential. As the positive test charge moves through the external circuit from the positive terminal to the negative terminal, it decreases its electric potential energy and thus is at low potential by the time it returns to the negative terminal.
If a 12 volt battery is used in the circuit, then every coulomb of charge is gaining 12 joules of potential energy as it moves through the battery. And similarly, every coulomb of charge loses 12 joules of electric potential energy as it passes through the external circuit. The loss of this electric potential energy in the external circuit results in a gain in light energy, thermal energy and other forms of non-electrical energy.
With a clear understanding of electric potential difference, the role of an electrochemical cell or collection of cells i.
BBC - GCSE Bitesize: Current and potential difference
The cells simply supply the energy to do work upon the charge to move it from the negative terminal to the positive terminal. By providing energy to the charge, the cell is capable of maintaining an electric potential difference across the two ends of the external circuit.
Once the charge has reached the high potential terminal, it will naturally flow through the wires to the low potential terminal. The movement of charge through an electric circuit is analogous to the movement of water at a water park or the movement of roller coaster cars at an amusement park.
In each analogy, work must be done on the water or the roller coaster cars to move it from a location of low gravitational potential to a location of high gravitational potential.
Once the water or the roller coaster cars reach high gravitational potential, they naturally move downward back to the low potential location. For a water ride or a roller coaster ride, the task of lifting the water or coaster cars to high potential requires energy. The energy is supplied by a motor-driven water pump or a motor-driven chain.
In a battery-powered electric circuit, the cells serve the role of the charge pump to supply energy to the charge to lift it from the low potential position through the cell to the high potential position.
It is often convenient to speak of an electric circuit such as the simple circuit discussed here as having two parts - an internal circuit and an external circuit. The internal circuit is the part of the circuit where energy is being supplied to the charge. For the simple battery-powered circuit that we have been referring to, the portion of the circuit containing the electrochemical cells is the internal circuit.
GCSE Science/Current, voltage resistance and Ohm's law
The external circuit is the part of the circuit where charge is moving outside the cells through the wires on its path from the high potential terminal to the low potential terminal. The movement of charge through the internal circuit requires energy since it is an uphill movement in a direction that is against the electric field.
The movement of charge through the external circuit is natural since it is a movement in the direction of the electric field.
When at the positive terminal of an electrochemical cell, a positive test charge is at a high electric pressure in the same manner that water at a water park is at a high water pressure after being pumped to the top of a water slide. Being under high electric pressure, a positive test charge spontaneously and naturally moves through the external circuit to the low pressure, low potential location. As a positive test charge moves through the external circuit, it encounters a variety of types of circuit elements.
- Electric Potential Difference
- Charge, Current & Potential Difference
Each circuit element serves as an energy-transforming device. Light bulbs, motors, and heating elements such as in toasters and hair dryers are examples of energy-transforming devices.
In each of these devices, the electrical potential energy of the charge is transformed into other useful and non-useful forms. For instance, in a light bulb, the electric potential energy of the charge is transformed into light energy a useful form and thermal energy a non-useful form.
Current and potential difference
The moving charge is doing work upon the light bulb to produce two different forms of energy. By doing so, the moving charge is losing its electric potential energy. Upon leaving the circuit element, the charge is less energized. The location just prior to entering the light bulb or any circuit element is a high electric potential location; and the location just after leaving the light bulb or any circuit element is a low electric potential location.