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Electric Current

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Batteries
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Batteries

Credit: Anton Fomkin
Source: http://www.flickr.com/photos/antonfomkin/3046849320/

Creating electrical energy via stored chemical energy, batteries are able to power the millions of devices that surround us every day.

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• A battery is a group of chemical cells where each cell consists of two metal plates, or electrodes, that are immersed in a conducting fluid. Due to a chemical reaction between the plates and the fluid, one of the plates becomes more positively charged than the other. Usually considered as ideal batteries, ideal batteries are a source of an electromotive force (emf) that is able to maintain a constant potential difference between the two terminals.
• All real batteries have an internal resistance, meaning the potential difference between the terminals is not the same as the electromotive force of the battery. In a real battery, there exists an internal resistance of the battery given by r. By creating a circuit diagram of a battery, it is easy to see that the voltage across the terminal in a real battery is given as:

$V_a-V_b=\varepsilon - Ir$

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Using the information provided above, answer the following questions.

1. A 9 Ω resistor is connected across a battery of emf 5 V and internal resistance of 1 Ω. What is the current?
2. If the emf of the battery is doubled, what would the current be in the previous problem?
3. Is the terminal voltage greater or less than the emf of the battery?