All voltage sources have two fundamental parts: a source of electrical energy that has a electromotive force (emf) and an internal resistance r.‎Introduction to · ‎The Origin of Battery Potential · ‎Internal Resistance and. Electromotive force (EMF) is equal to the terminal potential difference when no current flows. EMF and terminal potential difference (V) are both measured in volts, however they are not the same thing. EMF (ϵ) is the amount of energy (E) provided by the battery to each coulomb of charge (Q) passing through. Electromotive force, abbreviated emf is the electrical intensity or "pressure" developed by a .. Schaum's outline of theory and problems of beginning physics II.‎Notation and units of · ‎Formal definitions · ‎In thermodynamics · ‎Generation.


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In electromotive force physics for the negative charges to be moved to the negative terminal, work must electromotive force physics done on the negative charges.


This requires energy, which comes from chemical reactions in the battery. The potential is kept electromotive force physics on the positive terminal and low on the negative terminal to maintain the potential difference between the two terminals.

Electrical sources and internal resistance

An ideal battery is an emf source that maintains a constant terminal voltage, independent of the current between the two terminals. An ideal battery has no internal resistance, and the terminal voltage is equal to the emf of the battery.

In the next section, we will show that a real battery does have internal resistance and the terminal voltage is always less than the emf of the battery. The Origin of Battery Potential The combination of chemicals and electromotive force physics makeup of the terminals in a battery determine its emf.

The lead acid battery used electromotive force physics cars and other vehicles is one of the most common combinations of chemicals.


Figure shows a single cell one of six of this battery. The cathode positive terminal of the cell is connected to a lead oxide plate, whereas the anode negative terminal is connected to a lead plate.

Both plates are immersed in sulfuric acid, the electrolyte for the system. Chemical reactions in a lead-acid cell separate charge, sending negative charge to the anode, which is electromotive force physics to the lead plates.

The lead oxide plates are connected to the positive or cathode terminal electromotive force physics the cell.


Sulfuric acid conducts the charge, as well as participates in the chemical electromotive force physics. Knowing a little about how the chemicals in a lead-acid battery interact helps in understanding the potential created by the battery. Figure shows the result of a single chemical reaction.

Two electrons are placed on the anode, making it electromotive force physics, provided that the cathode supplies two electrons. This leaves the cathode positively charged, because it has lost two electrons. In short, a separation of charge has been driven by a chemical reaction.

Electromotive force | physics |

Note electromotive force physics the reaction does not take place unless there is a complete circuit to allow two electrons to be supplied to the cathode. Under many circumstances, these electrons come from the anode, flow through a resistance, and return to the cathode.

Note also that since the chemical reactions involve substances with resistance, it is not possible to electromotive force physics the emf without an internal resistance.

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