# Tag Info

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Batteries usually use electro-chemical reactions to store energy. These reactions have a limit to how fast they can transfer that energy. For example, a typical lead acid car battery can only draw so much energy; after a certain point it begins to break down, producing hydrogen gas which then can ignite with free oxygen in the air. An analogy would be a ...

47

Just to complement the other answers: This isn't really about Kirchhoff's law. Rather, it is about an idealised situation that does not have a solution at all. When you draw such a diagram, you can think of it in two ways: As a sketch of a real circuit. Then the voltage source is, e.g. a battery or a power supply, and the line is a wire. You can connect ...

45

tl;dr Batteries do not create electric fields to move charges. They move charges, which creates electric fields. a battery [...] gives out some electric field that moves through the circuit and gives a force on electrons in conductor to produce current. This description is, if not completely wrong, at least misleading. A battery is not a source of electric ...

44

The defibrillator requires a high voltage to do its job. ordinarily this would require a very large battery stack (hundreds of individual cells) to achieve the voltage requirement. Instead, defibrillators use a smaller battery pack to drive a chopper circuit that steps the voltage up through a transformer, after which the result is rectified, filtered, and ...

30

There will be an increase of the mass of the battery when you charge it, though that increase is going to be undetectably small. I would do the calculation in reverse i.e. start with a fully charged battery and calculate how much it decreases in mass when you run it down. The mass decreases because the battery does work $E$ on the electrons that flow ...

30

Think of a battery as an escalator (potential gravitational energy and potential electric energy/voltage are analogous here). If you have two escalators side by side, taking either one will get you to the same height. If you have two escalators in a row, you will have to take them both and therefore get twice as high. The advantage of escalators side by side ...

29

Sometimes it is easier to understand circuitry in the context of water. What you're imagining is two tanks of water of equal size linked together by a pipe that has been sealed off. If one tank holds 5% water and the other holds 35% water, when you remove the seal, the tanks equalize and you end up with 20% in both tanks. What you're forgetting is that ...

25

It is energetically unfavourable to split a water molecule into the two ions $\text{H}^+$ and $\text{OH}^-$ i.e. you need to put in energy to do it. However at room temperature water molecules have a range of energies and there are always a few molecules with enough energy to ionise. So any sample of pure water at everyday temperatures always contains a few $... 25 The short answer is that although capacitors do not hold as much total energy as a battery the same size, they can release energy faster than batteries can. In a portable defibrillator (or a taser!) a battery charges a capacitor, then the capacitor releases the the charge into the subject much, much faster than it could have been supplied directly from the ... 24 The key here is the voltage of both the batteries. The battery in the phone is generally at a voltage of 3.7V. The battery pack has a higher voltage or a circuit which gives a voltage of 5V to your phone. So, as long as the voltage with which you charge the phone is higher than that of the battery, the percentage of power in it doesn't matter and the phone ... 24 Connecting your phone to the battery pack doesn't directly connect the cells in parallel. I assume this is where your guess of an equilibrium with equal voltage -> equal charge percentage comes from. Shorting lithium-ion / lithium-polymer (LiPo) cells together like that would likely cause one or both to literally catch fire from the high currents, or from ... 24 The ability to deliver energy relatively quickly is basically the distinction between a "capacitor" and a "rechargeable battery". This isn't a physics factoid so much as just what the words mean. For example, in the below plot:$ {\require{color}} {\definecolor{capacitor}{RGB}{255,10,10}} {\definecolor{lightCapacitor}{RGB}{255,131,131}} {\definecolor{...

23

There are many reasons for this situation. Power produced is non-adjustable. The battery produces power at nearly constant rate (slowly decaying with time). It cannot be increased and if not consumed (or stored) the power is lost. (Mentioned by DumpsterDoofus) low power density. ${}^{63}\text{Ni}$ for instance produces ~5 W/kg (and kg here is just mass of ...

21

It will normally just reach the negative terminal. Generally, current only flows in closed circuits. Hence, it could only flow into the ground if the positive terminal was also connected to ground, for example if you touch the positive terminal and you stand on the ground with bare feet or so. Then you might ask, what the purpose of grounding is. The ...

20

Batteries do not behave in such an ideal way across all conditions. The simplest model of a battery as a circuit element is the one you describe - a pure voltage source. A slightly-more sophisticated model is as a voltage source connected to a fixed resistor, called the battery's internal resistance. A typical battery has an internal resistance of between 1 ...

19

The law does hold up perfectly here. There's a battery, with v volts. Let's use 5v. Then, there's a wire. In the circuit above, there will be some (high) current going through the wire and by ohm's law, some voltage drop will appear. -5v, actually. 5v + -5v = 0. Solved. The 5v for the battery is a fixed value. If you want to solve for the current, you can ...

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Another intuition: both circuits are the same but in reverse from the point of view of the center wire, so each provides the same current but in opposite directions, thus cancelling each other.

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In ideal circuit theory, the parallel connection of two voltage sources results in an inconsistent equation, e.g., a 3V and 2V source connected in parallel, by KVL, gives the equation: 3 = 2. In the real world, batteries are not ideal voltage sources; batteries can supply a limited current and the voltage across the battery does, in fact, depend on the ...

16

You should not connect different batteries in parallel. If you do, the battery with the highest voltage will discharge into the other one, until they end up with equal voltages. If the second battery (the lower voltage one) is a rechargeable, then it will be charged by the first one, again until the two have the same voltage. In this case the end voltage ...

16

Since you seem to be eager for an analogy-free answer, I'll try to give it a stab. I think this question is actually a bit deeper than some of the answers are giving it credit for, and so far I think trentcl answers your question the best: the root cause of your confusion is that you are assuming that batteries act as sources of fixed fields, rather than ...

14

The key thing is that there is NO electric field within the perfect wire. So, there is no force acting on the electron, and thus no work done on it (while it's in the perfect wire). This goes back to the definition of a perfect conductor (which the perfect wire is). Within a perfect conductor, there is no electric field. Instead, the charges (which have ...

14

Mostly the problem is that in batteries, current flow is not by electrons as in something like a copper wire, but by physical movement of ions. Only so many ions can migrate to the right place and perform the right chemical reaction over some fixed time.

14

Consider the potential. Let’s call the left upper corner A and right upper corner B. First see upper side. There are two batteries and they’re symmetric. It is easy to imagine that the potential of the mid point of the upper side is the average of A and B. Then see the bottom side. It’s also symmetric. So the potential of the mid point of the bottom side ...

13

Consider for a moment, a cell that is not connected to a circuit, i.e., there is no path for current external to the cell. The chemical reactions inside the cell remove electrons from the cathode and add electrons to the anode. Thus, as the chemical reactions proceed, an electric field builds between the anode and cathode due to the differing charge ...

13

Short answer: Potential is defined depending on the choice of a origin (e.g. ground). The positive plate of a capacitor has potential $Q/C$ greater than negative plate of the same capacitor. We do not know its potential compared to anything else, unless we know how they are connected in a circuit. Here the points a and b are connected by an ideal conducting ...

13

A battery, ideal or not, does not follow Ohm’s law. Ohm’s law is an observed behavior of a specific class of materials/devices, sometimes called a constitutive equation. It is not a universal law of nature. Not all materials/devices obey it, including batteries.

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Heat. Batteries have internal resistance and so produced heat when current flows through them (Joule heating). Also, the heat generated increases by the square of that current. E.g, doubling the charging current causes the heat produced to be increased 4 times. Ultracapacitors are a different technology that can be used like batteries--they have very very ...

12

The resistance of water, even with ions and minerals and such, is still fairly high. So, a tiny current flowed through the water, but not very much. Additionally, the heating effect that often destroys them when short circuited would also be nullified by the cooling water.

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One aspect that hasn't been covered in the other answer is what is really needed to make a defibrillator work reliably and safely. Defibrillating a heart isn't simply "OK, let's electrocute the patient"! In order not to damage the heart, a very careful application of energy is needed. That means that the defibrillator must create a "well behaved" electrical ...

12

Kirchoff's law only applies to consistent circuits. It is possible to write a circuit which is not self-consistent using ideal wires and ideal batteries, but any tool which gives you a solution for the circuit will have to fail because there is no such solution in the first place. In this case, if you work out the equations, you see that you have an ...

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