Compare the resistances and electromotive forces for the voltage sources connected in the same and opposite polarity, and in series and in parallel. When more than one voltage source is used, they can be connected either in series or in parallel, similar to resistors in a circuit.
When voltage sources are in series facing the same direction, their internal resistances add and their electromotive force, or emf, add algebraically. These types of voltage sources are common in flashlights, toys, and other appliances. Usually, the cells are in series in order to produce a larger total emf.
Flashlight and Bulb : A series connection of two voltage sources in the same direction. This schematic represents a flashlight with two cells voltage sources and a single bulb load resistance in series.
A battery is a multiple connection of voltaic cells. The disadvantage of series connections of cells in this manner, though, is that their internal resistances add. This can sometimes be problematic. For example, if you placed two 6v batteries in your car instead of the typical 12v single battery, you would be adding both the emfs and the internal resistances of each battery.
You would therefore end up with the same 12v emf, though the internal resistance would then be doubled, causing issues for you when you want to start your engine. But, if the cells oppose one another—such as when one is put into an appliance backwards—the total emf is less, since it is the algebraic sum of the individual emfs.
When it is reversed, it produces an emf that opposes the other, and results in a difference between the two voltage sources. Battery Charger : This represents two voltage sources connected in series with their emfs in opposition.
Current flows in the direction of the greater emf and is limited by the sum of the internal resistances. Note that each emf is represented by script E in the figure. A battery charger connected to a battery is an example of such a connection. The charger must have a larger emf than the battery to reverse current through it. When two voltage sources with identical emfs are connected in parallel and also connected to a load resistance, the total emf is the same as the individual emfs.
But the total internal resistance is reduced, since the internal resistances are in parallel. Thus, the parallel connection can produce a larger current. Two Identical EMFs : Two voltage sources with identical emfs each labeled by script E connected in parallel produce the same emf but have a smaller total internal resistance than the individual sources. Parallel combinations are often used to deliver more current. The output, or terminal voltage of a voltage source such as a battery, depends on its electromotive force and its internal resistance.
Express the relationship between the electromotive force and terminal voltage in a form of equation. When you forget to turn off your car lights, they slowly dim as the battery runs down. Their gradual dimming implies that battery output voltage decreases as the battery is depleted. The reason for the decrease in output voltage for depleted or overloaded batteries is that all voltage sources have two fundamental parts—a source of electrical energy and an internal resistance. All voltage sources create a potential difference and can supply current if connected to a resistance.
On a small scale, the potential difference creates an electric field that exerts force on charges, causing current. We call this potential difference the electromotive force abbreviated emf. Emf is not a force at all; it is a special type of potential difference of a source when no current is flowing.
Units of emf are volts. Electromotive force is directly related to the source of potential difference, such as the particular combination of chemicals in a battery.
However, emf differs from the voltage output of the device when current flows. The voltage across the terminals of a battery, for example, is less than the emf when the battery supplies current, and it declines further as the battery is depleted or loaded down.
The voltage output of a device is measured across its terminals and is called its terminal voltage V. Terminal voltage is given by the equation:. Schematic Representation of a Voltage Source : Any voltage source in this case, a carbon-zinc dry cell has an emf related to its source of potential difference, and an internal resistance r related to its construction. Note that the script E stands for emf.
Also shown are the output terminals across which the terminal voltage V is measured. I is positive if current flows away from the positive terminal. The larger the current, the smaller the terminal voltage. Likewise, it is true that the larger the internal resistance, the smaller the terminal voltage. Privacy Policy. Skip to main content. Circuits and Direct Currents. Thanks for the tutorial Salty but about 3. It's the law, if one doesn't like that law then petition the government to change it If deer cross at an unsafe part of road, move the deer crossing sign, not the road.
That is economics. Moving it right or left is political. Forrest Mims - Getting Started in Electronics. I dont trust Forrest Mims. This myth got propagated to an article in Nuts and Volts magazine. It is really easy to test. He may be good in other things, but he sure got that wrong. What I said about Forrest Mims is only partially true. I use clear LEDs, and in that case what I said is true.
A photon of higher energy than the emitted color of the LED will kick electrons across the band gap and give a voltage. However, if you use LEDs that have a colored plastic case, only photons of that color will get through, so you can have a narrow detection band, like Forrest Mims claims.
He must have been using old fashioned cheapy LEDs. High quality LEDs are clear and the color is precisely defined by the band gap of the diode. The quality of the LED has nothing whatsoever to do with the colouring of the package or lack thereof.
Every forum need one person who says dumb stuff without thinking. That seems to be my role here. So I advise you to get a bunch of batteries and one or 2 multimeters and start doing some measurements. The Big concept here is that there does not exist a "universal ground" to which the batteries are referenced. You can add or subtract the voltage difference the battery creates from another voltage difference.
If you connect it properly then a transistor inside that voltage regulator will be adjusted to try to keep the voltage between the "GND" pin and the "output" pin of the LM close to 5V. If you add a 3V batery to the output or to the ground pin of the LM you can add or subtract the 3V of the battery to the 5V. Skip to main content. WHY do voltages add up in a series circuit? Log in or register to post comments. Go To Last Post. Level: Hangaround. Posts: View posts.
Posted by zedeneye1 : Sat. Nov 30, - PM. Fivestar widget 1 2 3 4 5. New Bitmap I2mage. Tags: Learning and Information , General Electronics. Posted by bobgardner : Sat.
Log in or register to post comments Top. Posted by JohanEkdahl : Sat. Level: Resident. Level: Raving Lunatic. Posted by smileymicros : Sat. Level: Moderator. Posted by js : Sat. John Samperi Ampertronics Pty. Posted by sparrow2 : Sun. Dec 1, - AM. Level: Posting Freak. Posted by johnrk : Sun. It could be worse - the OP could be a lobbyist : If you connect the positive terminal to the negative terminal you will get a complete path with nothing to inhibit current flow except the internal resistance of the source.
It is important to note that all the analogies above talk about potential energy in a pressure analogy and kinetic energy flow rate Here is a great link You seem to be focused on only the voltage portion of the problem.
Posted by zedeneye1 : Sun. I think I need to study electricity properly Anyone recommend a book? And thanks to everyone for helping And also, I'm a "hobyyist". Posted by smileymicros : Sun. Posted by Visovian : Sun. Dec 1, - PM. Dec 3, - PM. Posted by valusoft : Wed. Dec 4, - AM. Hi Lee et al, I like the ladder analogy. Cheers, Ross. Yes that is about as simple as it gets! Posted by westfw : Wed. Ladders, and Visovian's Barrels, are good analogies. Posted by Chuck-Rowst : Wed.
Dec 4, - PM. Posted by Torby : Wed. If you don't know my whole story, keep your mouth shut. Posted by ka7ehk : Wed. So, forget about the non-question and get on with life! Jim, Answers to your example questions have been proposed by some of the greatest minds of man in the past.
Why does water flow downhill? Sir Isaac Newton said it was "gravity". Posted by larryvc : Wed. Let's try another picture I "know" all those arguments that Chuck presented. Would not have a PhD in E. Posted by smileymicros : Wed. What does 'why' mean?
What does it mean to 'understand' something? Posted by microcarl : Wed. It's a law of physics, nothing more Posted by microcarl : Thu. Dec 5, - AM. Posted by JohanEkdahl : Thu. Interesting posts Jim, and woth to ponder several times. Level: Rookie. Posts: 45 View posts. Posted by yhikum : Thu. Dec 5, - PM. Posted by JohanEkdahl : Fri. Dec 6, - AM. Those seems to be very good reads, indeed! I see some week-end reading coming up.. Posted by toalan : Mon.
Dec 9, - PM. Posted by microcarl : Mon. Posted by yhikum : Wed. Dec 11, - PM. I wonder if observing voltage summation would work the same for magnets. Do we need to know how an internal combustion engine works, in order to drive a motor vehicle? Do we need to know how Natural Gas combusts, before we use a cook stove? Take the basic concept, accept it, and get to the task at hand!
No offense meant to anyone! Level: New Member. Posts: 1 View posts. Posted by SaltyToothpaste : Wed. Jun 28, - AM. Posted by js : Wed. Posted by awneil : Wed. Well, as the dead thread has been re-animated, Posted by KitCarlson : Wed. Posted by MarkThomas : Wed. Jun 28, - PM. Last Edited: Wed. Would it not be more "economics" to leave everything as they are and EAT the deer?
Posted by MarkThomas : Thu. Jun 29, - AM. Active 1 year, 5 months ago. Viewed 24k times. Add a comment. Active Oldest Votes. Two water pumps in parallel can produce twice the water flow of one ideally.
Two water pumps in series can produce twice the pressure or head of one ideally. Alfred Centauri Alfred Centauri But, within the electrolyte, the electric current is due to ions, not electrons. Technically there is some movement in both directions, but that in one direction outweighs the other by orders of magnitude.
Show 4 more comments. SaltyToothpaste SaltyToothpaste 31 1 1 bronze badge. Rich Klingler Rich Klingler 31 4 4 bronze badges. Lets us think about this in the physics perspective. Here my theory so to speak A to B When electrons leaves from the negative terminal of A to enter to the positive terminal of B, they have potential energy U of qV.
This is the potential energy carried by the electrons flowing through the circuit. Bania J. Fonseca Bania J. Fonseca 1. But the notion of voltage doesn't require any electrons to move or current to flow. The potential difference across 3 cells is what it is regardless of current flow. Sign up or log in Sign up using Google.
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