Current, Voltage and Power | A Level Notes
electric charge, electric current, potential Difference, Microscopic picture of current in a wire, Conductors, Conductance, Conductivity An introduction to Electricity and Strength of Materials with Peter Eyland . For metal wires, the relationship between current and potential difference is I = GV, or V = RI . Summarising. a source of voltage or potential difference (V) like a battery, power supply, solar cell, Resistance increases (and current decreases) as resistors are added in. Electronics Tutorial about the Relationship between Voltage Current and Resistance in an The Potential difference between two points is measured in Volts with the circuit Batteries or power supplies are mostly used to produce a steady D.C. (direct current) voltage . A basic summary of the three units is given below.
Resistors in Circuits
In the first classical model of electrical conduction, the Drude modelwas proposed by Paul Drudewhich finally gave a scientific explanation for Ohm's law. In this model, a solid conductor consists of a stationary lattice of atoms ionswith conduction electrons moving randomly in it.
A voltage across a conductor causes an electric fieldwhich accelerates the electrons in the direction of the electric field, causing a drift of electrons which is the electric current.
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. 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. Any given material will break down under a strong-enough electric field, and some materials of interest in electrical engineering are "non-ohmic" under weak fields.
In the early 20th century, it was thought that Ohm's law would fail at the atomic scalebut experiments have not borne out this expectation. As ofresearchers have demonstrated that Ohm's law works for silicon wires as small as four atoms wide and one atom high. Drude model The dependence of the current density on the applied electric field is essentially quantum mechanical in nature; see Classical and quantum conductivity.
Electronics/Voltage, Current, and Power - Wikibooks, open books for an open world
The current in the loop is the result of these two choices. Much more on this in the SPT: Electricity and energy topic. The relationship between the push of the battery and the size of electric current is summarised by: According to this relationship, if the resistance does not change, then increasing the voltage results in an increase in current. There is a 0.
Ohm's law - Wikipedia
Double the battery voltage gives double the current. The answer to this question takes us back to the detailed explanation, introduced in episode 01, of how electric circuits work. When a second battery is added to a circuit, increasing the voltage, the effect is to strengthen the electric field around the circuit, between the positive and negative terminals of the battery.
There is a greater force or push on each and every charge in the circuit due to the stronger field in the wire as the positive terminal becomes more positively charged with respect to the negative terminal. This stronger field produces a greater acceleration of charged particles between interactions with the ions in the filament of the bulb, and so more energy is shifted from charge to ion during each interaction.
So, at one and the same time, increasing the voltage results in a bigger push on each charge and more power being switched by the current. Set up a situation where current in the resistance such as a bulb is one ampere and the voltage across the bulb is also one ampere. As a result one joule of energy is being shifted per second.
This is electrical working; see SPT: Set up a situation where the current in the resistance is smaller and the energy being shifted will also be reduced.
Accumulating energy in a store So, for a fixed voltage, the energy accumulates steadily in the thermal store of the surroundings. The energy shifting from the chemical store also depletes that store by the same amount each second. Change the flow of charge, and you change the energy shifting: The voltage across the bulb or any other resistor determines how much energy is shifted to the surroundings as each coulomb of charge passes through.
The voltage is the energy shifted per unit charge.mr i explains: Current-Potential Difference Graphs and Resistance
The voltage across the battery sets the amount of energy which is shifted from the battery per coulomb of charge that has passed. You can rewrite the definition above for a duration of one second: As the brightness of bulbs depends on the power, rather than the accumulated energy, this may make better connections with what is seen and easily felt to be important.
The brightness is the result of two electrical factors: If these current and voltage figures are taken together, we can see that in the bulb there's continuous activity: Energy is shifted or transferred by the circuit: What you have calculated here is the energy shifted every second by the electrical working pathway — that is the power input. All of this ends up heating or lighting. The power input is equal to the power output: You can write this as: This idea can be applied to electrical devices, mechanical machines and even to people.