68 votes

Why do we use capacitors and not batteries in defibrillator?

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 ...
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48 votes
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Why doesn't Kirchhoff's Law work when a battery is shorted with an ideal wire?

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 ...
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  • 3,658
46 votes

Why doesn't the voltage increase when batteries are connected in parallel?

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 ...
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  • 561
44 votes

Why do we use capacitors and not batteries in defibrillator?

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, ...
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30 votes

Increase in mass of battery of my smartphone

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 ...
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30 votes

Why doesn't the voltage increase when batteries are connected in parallel?

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 ...
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  • 5,955
29 votes

How can a battery charge up another battery to a higher percentage?

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 ...
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  • 745
25 votes
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Does current run forever in water? (assuming the supply voltage is there forever)

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 ...
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25 votes

Why do we use capacitors and not batteries in defibrillator?

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!) ...
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  • 371
24 votes

How can a battery charge up another battery to a higher percentage?

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 ...
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  • 980
24 votes
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How can a battery charge up another battery to a higher percentage?

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. ...
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  • 1,364
24 votes

Why do we use capacitors and not batteries in defibrillator?

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. ...
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  • 4,564
21 votes
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How does grounding work?

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, ...
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  • 6,930
19 votes

Why doesn't Kirchhoff's Law work when a battery is shorted with an ideal wire?

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 ...
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  • 933
17 votes
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I Do Not Understand a Textbook Example: Calculating Voltage Across a Resistor

The book is indeed wrong and the quoted answer $V=0.5\ \text{volts}$ does not appear to make any sense. Using conservation of energy, one can compare the power going into the source and the power ...
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17 votes
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Is every finite circuit "solvable" using Ohm's law and Kirchhoff's loop rules?

The other answers have noted that the total number of equations is correct, but that's not actually enough to guarantee a unique solution. There are at least two ways things can fail: The equations ...
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16 votes

Why does connecting a battery's positive terminal to the negative terminal of another battery not create a short circuit?

I think this picture answers the question: The battery's terminals are not charged. It's just a chemical reaction that starts the charge. There's a $\text{Zn}$ and a $\text{CuSO}_4$. When they meet ...
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  • 161
16 votes

Why doesn't the voltage increase when batteries are connected in parallel?

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 ...
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15 votes

Understanding the zero current in a simple circuit

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 ...
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15 votes

Why is there an electric field around this closed electric circuit?

Isn't the electric field guided entirely through the wire? The wires are (very nearly) perfect conductors, and therefore the electric field within the wires is (very nearly) zero. why is there an ...
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14 votes
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Why does a drop in resistance lead to a drop in voltage?

There are three voltages in this circuit: the voltage, $V_{batt}$ across the battery terminals, the voltage, $V_r$ across the fixed resistor, $r$, and the voltage, $V_R$, across the variable resistor. ...
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13 votes
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What maintains constant voltage in a battery?

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 ...
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13 votes

Why is there no current between two capacitors connected in series?

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 ...
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13 votes

Does current pass through an ideal battery?

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 ...
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13 votes

Proof of internal resistance acting like it does

Internal resistance is just a concept for approximating the non ideal behaviour of a battery. This latter is ideally defined as a device that is capable of provinding a constant voltage regardless of ...
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13 votes
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Why are potential drops concentrated at resistive elements?

That the potential drop across an ideal (resistivity $\rho = 0$) wire is zero is a consequence of Ohm's Law: $$\mathbf{E} = \rho\,\mathbf{J} = \mathbf{0} \Rightarrow \Delta V = -\int{\mathbf{E}\cdot\,...
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12 votes
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Battery charging a Capacitor

I understand also that there would be a tiny minuscule resistive loss through the wire, but really it's not enough to say anything about. On the contrary, it's crucial. Assuming an ideal voltage ...
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12 votes

Why do we use capacitors and not batteries in defibrillator?

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 ...
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12 votes

Why doesn't Kirchhoff's Law work when a battery is shorted with an ideal wire?

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 ...
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