# Questions tagged [voltage]

Voltage is the unit of measurement for electronic potential, from one point location to another.

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46 views

### What is difference between current and voltage? [closed]

If current passes through the bulb not using it up then how battery becomes weak after sometime?
35 views

### Why is the open circuit voltage equal to Thevenin's Equivalent Voltage?

When we are taught Thevenin's Theorem, we are taught that the equivalent voltage Vth is the voltage obtained at terminals A-B of the network with terminals A-B open circuited. But why is it true?
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### How is a capacitor implemented in Kirchoff's Loop Rule?

I'm real stumped here. I may be missing something, but I'm genuinely perplexed as to how one would add a capacitor to the list of elements being added to an equation through Kirchoff's Loop Rule (KVL)...
332 views

### Why isn't there a minus sign in Ohm's law, $V = IR$?

Suppose current runs through a resistor from left to right, and we define the left-to-right direction as positive. Then from left to right, the potential decreases. So $V,$ the voltage across the ...
275 views

### Principle of potentiometer

I could not understand why the emf of the main cell (labelled E) in the circuit (can be a battery eliminator) should be greater than the emf of the cells (E1 and E2) used in the secondary circuit. ...
112 views

### Ohm's Law and transmission of electricity

Electricity is transmitted at high voltages. It is said that this reduces current and consequently resistance. But according to ohms law, low current must face high resistance. How is this ...
80 views

### What does 'Oppose a Change in Current' really mean from Lenz Law?

We all know what Lenz Law is, but I have a bit of trouble conceptualizing the phrase above. Does 'Oppose a Change in Current' means it will take more time for the current to increase to its maximum ...
58 views

### What am I doing wrong in electrolysis of water?

I am trying to two 1.5V battery in series to electrolysis a small bowl of tap water oversaturated with salt. But I can't see any bubble on the part submerged (circled on the photo). Could you guys ...
1k views

### Why is there an induced EMF in a plastic ring?

If we were to pull a plastic ring across the boundary of a magnetic field, why does an emf form? If this was a metal ring I would fully understand because the electrons are free to move in a metal ...
37 views

### How can Resistance be transferred across in a Transformer?

Can someone tell me how the resistor could be transfered from the secondary to the primary side? Could you give me a concise explanation on how it's possible? A simple analogy/analysis would be very ...
56 views

### Why this transformer have different power input & output?

Assume an ideal transformer with the same number of windings, the primary windings generate 50VAC, 10Amps (5Ohms), the secondary side has a 10 Ohms resistor, if the voltage induced on the secondary ...
49 views

### How to compute the self-capacitance of a conductive shape?

(Depending on the answers given, this question might be better suited for Math.SE, but I don't think so.) I recently learnt about the notion of self-capacitance of a conductive shape, which now seems ...
196 views

### Potential Difference of a battery - What does it mean?

I have studied current electricity for a while now. When I look back at basic concepts, I am quite clear about what current, electron, resistance is. But I cannot imagine about the potential ...
78 views

### Potential difference of resistors in parallel linked systems

Before the question I want to explain somethings to see if I understand anything wrong please tell me if im wrong: When there is a Potential difference on a system then the electrical charge will move ...
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### How to estimate energy of piezo igniter discharge?

Question for fun. We all know piezo igniters, these small friends, like following one: All of them are probably quite similar: same spring, same piezo, same hit force, and so on. Also I have some ...
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### Will there be an induced EMF if the windings have no resistance?

Imagine a transformer, the primary has a voltage source, a 5 Ohms resistor, and obviously the windings too. If there were no resistance on the windings will there be any emf induced on the secondary ...
114 views

### The flow of electric current

If positive charges have higher electric potential difference than negative charges then why the negative charges (electrons) are the one that are moving in a circuit? and to my knowledge the ...
251 views

### Unequal area's under a graph of induced voltage (magnet falling through a coil) against time - Faraday's Law

I have done an experiment where a magnet was dropped through a coil of wire and the induced emf was recorded. My understanding is that the area's under the positive and negative sections of the ...
108 views

### Should a Step Up transformer necessarily need more Windings?

The Primary & Secondary has the same number of coils/windings, but the resistors on them are different, using P=I2 × R, we get that the current in the Secondary side decreases and Voltage ...
332 views

### Van de graaff generator, Leyden jars and capacitance

How will the capacitance of a typical desktop van de graaff generator be affected when connected in series to a group of some 5-10 Leyden jars? I know that the capacitance is decreased in series ...
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### How to understand Kirchhoff's Voltage Law?

I'm having a hard time trying to understand why Kirchhoff's Voltage Law is true. I looked for an answer on the forum but I couldn't find a convincing one. So my question is : How to "physically" ...
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### What is meant when we say “any solution is *the* solution” due to the uniqueness theorem?

I understand the proofs for the uniqueness theorems in electrostatics, but I'm having trouble understanding their application to problem solving. A classic example is a system of concentric shells of ...
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### How do I solve for the voltage on a geometry that has varying thickness of a conductive metal?

I currently have a 3D geometry which is made from an isotropic material. In my case this material is simply a highly conductive metal. We can think of this geometry almost as a thin film with slightly ...
113 views

### Why Voltage Increases in a step up Transformer rather than the Current?

In a step up transformer, we all know voltage increases and current decreases, the answer to more voltage is because it has more windings, but why does more windings induce more voltage, can't the ...
57 views

### What possible advantage could there be in connecting several identical batteries in parallel? [duplicate]

In two-cell flash light,the batteries are usually connected in series. Why not connect them in parallel?
46 views

### How does a piece of wire know there is a voltage potential different?

Imagine water molecules inside a water pipe is moving due to difference in pressure, this pressure can be due to difference in gravitational potential or external force like somebody squeezing at one ...
22 views

### How to derive reflected waves in AC circuit?

I was reading the wikipedia page "Reflections of signals on conducting lines". In the section "Arbitrary impedance" they consider a circuit consisting of an alternating source $2V_i$ and two ...
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### Is the magnetic field cancelled out in a transformer?

https://physics.stackexchange.com/a/153501/213243 In the 3rd paragraph it is said that the magnetic field from the primary windings is cancelled out by the induced current from the secondary windings....
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### Does Kirchhoff's Law always hold?

There's a bit of furore from this question on Youtube involving Dr. Walter Lewin and another Youtuber. With Dr. Lewin claiming Kirchhoff's Law doesn't always hold when magnetic fields are involved, ...
42 views

### What is the energy loss when charging a phone battery with another battery [closed]

I'm curious to find out what the energy loss is when an external battery pack charges up another battery, say one in a mobile phone. Say my phone's battery has a capacity of 1000 mAh, and my ...
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### Voltage across parallel resistances

A resistor is connected to a battery of certain potential difference, it has now $V$ volt potential difference across its ends, after some time a resistor is connected in parallel with it. How does ...
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### Defining potential of the ground

In electronics, it is customary to define the potential of ground (thinking the Earth as a large conductor) as zero. Is this consistent with the fact that the Earth has a net electric charge that is ...
21 views

### Why does a stepup transformer increases voltage but reduces current?

I know its a really basic question knowing the fact that you could just plug in the Voltage and Current into the proportionality formula. The thing is that I want a 'scientific/logical' explanation ...
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### Magnetic field and magnetic forces and polarity

When the polarity of the voltage applied to a DC motor is reversed, the direction of motion does not reversed. Why not? How could the direction of motion be reversed?
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### How do I determine the accuracy of this two-dimensional potential field?

Let's say I want to solve this problem. I know the values on the boundaries and I guess an initial solution on the rectangular grid inside these boundaries, see figure below. Potential=10 on ...
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### What is the voltage in electrical circuits?

I understand what the voltage is and I realize that the battery makes an electric field due to the accumulation of the charges in the anode and cathode this electric field causes electric potential ...
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### Is voltage basically the measure of the strength (or density) of an electromagnetic field? And does an increase in voltage increase the amperage?

I have been in the process of fully understanding what is generally accepted as truth by the scientific community regarding voltage, watts, and amperage. Most engineers seem to say to simply use the ...
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### Griffiths Multipole Expansion and $Q$ going to zero

Griffiths states that given the multipole expansion: $$V(\vec{r})=\frac{1}{4\pi\epsilon_o}\sum_{n=0}^\infty\frac{1}{r^{(n+1)}}\int(\vec{r}')^nP_n(cos(\theta')\rho(\vec{r}')d\tau'$$ for large $r$ the ...
8k views

### Why does a 60W bulb glow brighter than a 100W bulb in a series?

In my physics class I have this problem that shows two lightbulbs, one 60W and one 100W in series, connected to a 120V battery. The problems are: Which bulb is brighter? (A: 60W) Calculate the ...
4k views

### Understanding voltage and power in the fluid analogy for DC circuits

I am trying to understand electric circuits (ie voltage, current, power, and resistance). For the most part, everything makes perfect sense, but for some reason I do not feel as if I understand the ...
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### Grounding and equipotential lines

In my textbook it says: One of the rules for static electric fields and conductors is that the electric field must be perpendicular to the surface of any conductor. This implies that a conductor is ...
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### Field between 2 electrodes experiment

We were asked to conduct an experiment that is as follows: Connect 4.5V constant voltage across 2 electrodes of thin Cu wire, dipped in a tub of copper sulfate solution. A needle is connected to a ...
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### Confusion about calculating resistances & terminal voltage

I'm looking at an exercise where a battery is powering two parallel light bulbs. Given are the battery's EMF ($12.0 V$) and its terminal voltage in this particular circuit ($11.8 V$), as well as the ...
1k views

### What's the reason behind the current remaining the same after passing by a resistance?

I've been wondering why does this really happen, I mean by intuition if electrons are driven by EMF (ignoring wire's resistance), $n$ coulombs would pass by a point per second, until they encounter ...
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### Kirchhoff's Voltage Law in a General Electromagnetic Field

Recently, Prof. Walter Lewin and YouTuber ElectroBOOM started a discussion about KVL, after Dr. Lewin claimed that KVL did not hold in the presence of an magneto-dynamic field. I would argue that Dr. ...
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### Capacitor demo explanation

I know that for a charged capacitor as one separates the plates further apart the voltage increases while the capacitance decreases. But surely as the plates are pulled further and further apart the ...
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### What is the difference between the voltage in the electrical circuit and electrostatics?

In electrostatics it depends on the distance from the charges, should it also be in the circuit? But in practice, the voltage depends on the resistance, for example on a resistor. And the distance ...
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### How do you calculate voltage drop in a neutral wire?

I've seen people saying that in practical situations, the voltage between the neutral wire and the ground is not exactly zero, is it true? And if yes, how do you find the voltage drop between these ...