# Tagged Questions

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

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### Can the potential difference produced in Van De Graff generator used to generate electric current?

If this machine can build up high voltages of the order of millions of volts, can we use this voltage to generate a current of electrons? The building up of potential difference can result in an ...
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### How is a variable potential divider able to reduce current/voltage through a component to zero, unlike a variable resistor?

For example, the diagram in my text book shows a filament lamp, in series with a uniform resistive wire, which can have its voltage and current varied by moving the sliding contact, e.g., a ...
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### How is a potential divider able to reduce current to zero?

For example, a filament lamp, in series with a uniform resistive wire, can have its voltage varied by moving the sliding contact, e.g., a rotatable wheel. However, why is a potential divider able to ...
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### What force causes the induced EMF of a loop? And, the difference between a loop EMF to motional EMF?

If a loop of wire is placed perpendicular to a changing magnetic field, there is an induced EMF such that the induced current is flowing in a direction to create an opposing magnetic field like this ...
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### Vibrational frequency of piezoelectric material

When a piezoelectric material experience a stress it generates voltage, and also when you applied voltage the piezo-material experience a vibrational frequency. Using oscilloscope we can determine the ...
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### Why ohm started his derivation from $V$ is directly propotional to $I$ but In his statment he says $I$ is directly propotional to $V$? [closed]

Why ohm started his derivation from $V$ is directly propotional to $I$ but in his statement he says I is directly proportional to V?
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### Why does vaccum have a nonzero characteristic impedance towards electromagnetic radiation

The characteristic impedance is calculated "as square root of the ratio of the permeability of free space ($\mu_0$) in henrys per meter ($\mathrm{H/m}$) to the permittivity of free space ($\epsilon_0$)...
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### Circuit with voltage source, resistance and current source

Suppose I have a (closed) circuit with a voltage source $V$, a resistance $R$ and a current source $I$ (in this order). Is it true that the voltage across the current source is $V-RI$ ?
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### Sign conventions for voltage drop and gain in circuit

In Sears and Zemansky's University Physics book and in many other books in English they define the following sign conventions (used for Kirchhoff loop rule for example): While in many other books (...
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### Measuring the barrier potential of a p-n junction

Is it possible to measure the potential difference across the depletion region (barrier potential) of a p-n junction using a voltmeter?
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### Spherical magnet inside a solenoid

When passing a bar magnet through a long solenoid why is it that the induced emf when the magnet is in the middle of the solenoid is zero? And if a spherical magnet is put inside the solenoid, will ...
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### Why does voltage remains same over Parallel Circuit

Why does voltage remains same over parallel circuit. If a resistor is connected in the circuit some of the charge should be transformed into heat and make a lack of charge after the resistor (in my ...
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### What is the voltage drop across a wire [closed]

If we attach a resistor in series, most diagrams only consider the voltage drop across the resistors. What happens when we remove all of the resistors? Why does the voltage drop across the wire become ...
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### How does voltage divided by EMF show efficiency?

I get that electromotoric force (emf) is energy per coulomb supplied and that voltage is energy per coulomb used but I don't get what it means when we say that the voltage divided by the emf gives the ...
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### Does the photoelectric effect obey Ohm's law?

I've been reading about the photoelectric effect for my modern physics class, and I was confused about how Ohm's law works in relation to it. Let's say we have a photoelectric apparatus that simply ...
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### Does voltage always cause current?

I'm wondering if the following statement is fully correct: Voltage causes current through a closed circuit, but through an inductor it is the change in current that causes a voltage. Obviously ...
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### Why does there have to be an electric field if there is potential difference?

I read in a few books that there is always an electric field if there is an electric potential. I went through this but the question on this page only states that there is an electric field and it is ...
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### Does charge of a metal charged by induction determine by which ends of the metal is grounded to?

Does charge of a metal charged by induction determine by which part of the metal is ground to? I draw a diagram to make it simple to understand: Right diagram: When ground is touched with the ...
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### Which power equation to use: $P = I^2 * R$ or $P = V^2 / R$?

Given are ideal max voltage $V = 200\;\mathrm{V}$ and max current $I = 5\;\mathrm{A}$. Therefore: ideal resistance is $$R = \frac VI = \frac{200 \;\mathrm{V}}{5\;\mathrm{A}} = 40 \;\mathrm{\Omega}$$...
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### Won't the Power be dissipated in the first quadrant of this graph?

In the following picture: In the first quadrant of the V-I graph(for an Independent Current Source, where the voltage supplied is positive on the top) won't the power be dissipated instead of being ...
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### Current and Resistance-Effects of the Length of the Wire

Two wires of the same material are both connected to a 9-V ideal battery. They have the same cross section area but wire 2 is twice longer than wire 1. Compare the following quantities by answering if ...
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### How can a battery charge up another battery to a higher percentage?

Say I have my phone on 5% and a large battery pack on 35% and I charge the phone. By the end the phone is on 100% and the pack is on 12%. How can the battery pack charge the phone up to a higher ...
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### How is a potential difference created between two points?

I would like to know how potential difference is created between two points?Is potential difference created by adding more electrons at one side?If that's the case how to add more electrons at one ...
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### How does back-emf oppose the input-current?

A circuit, has current $A$ flowing at a certain $V$. When there is a change in magnetic-flux, based on Faraday's law of induction & Lenz's law, we know that there is change in Potential ...
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### Charging by induction

When we charge an conductor by induction and grounding, we first bring a negative charge to the conductor. As a result the mobile electrons of the conductor get repelled and stay far from the negative ...
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### Poisson's equation with point source

PDE's are not my thing, but I'm trying to calculate the voltage in a finite conducting sphere, based on a point current source. With Poisson's equation of $\nabla^2\Phi = -\frac{J}{\sigma}$, where $J$...
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### Proof of Kirchoff's second law [closed]

There are 2 approaches I have stumbled to prove Kirchhoff's second law: Derive it from the conservation of energy. You can derive that from "integral of E*ds = 0". Can you show me a full or at ...
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### Elementary derivation of $P = UI$ starting from the definition of voltage as work done per unit charge

Consider the following elementary derivation of the formula $P = VI$ for Joule heating of a resistor $R$ for the dissipated power $P$ where the voltage over the resistor is $V$ and the current $I$. ...
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### Back EMF & Current, how can we make the current $I$ stable?

Lets assume we have a wire that has $10V$ across and $1$ $Amp$ flowing, now if this conductor is introduced to a changing magnetic field, $-EMF$ is induced, can we control our voltage to increase it ...
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### Li-ion Battery charging

Why are constant current mode and constant voltage mode needed when charging Li-ion batteries? Why do we apply saturation charge even after the cell voltage reaches 4.2V? What exactly is 'I-sense' in ...
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### Does charge injection from electrodes increases the total charge in a (semi)conductive channel?

When a (semi)conductor is connected to a voltage bias, a charge is injected by the electrodes. When steady state is reached (constant current flow), does the total charge of the (semi)conductor differ ...
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### Measuring voltage drop from induced current

I'm having trouble connecting voltage drops and induced current. Imagine you have a triangular loop make up off three resistors. You place this loop in a constantly changing magnetic field. This ...
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### Different voltage drops depending on the path

I was working through a problem in electromagnetic induction when I discovered that I have a fundamental ignorance of some sort that is puzzling me. Consider a circular wire, at rest, perpendicular ...
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### Voltage in parallel and series connection

In series connection, voltage is said to be different and current constant across the circuit. How does it come about ? Is it due to the accumulation of electrons on one side due to resistors? Or, if ...
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### What's the relation between output voltage and time to boil water given the same kettle?

An electric kettle rated 220V, 2000W needed 10 minutes to boil water when it is half filled with water in Singapore where the output voltage is 220V. Estimate the amount of time needed to do the same ...
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### Why do proportionality constants come on only one side?

We know that voltage is directly proportional to current. Then if we change proportionality to equality, we get $V=IR$. Why not $I=RV$??
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### How can be the neutral wire at 0 volts when current flowing through it?

Voltage is potential difference, and current flows because of voltage. So if the voltage is zero, how can current flow through the neutral wire.
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### How SPAD work over Break Down voltage?

SPAD (Single Photon Avalanche Detector) works beyond Breakdown Voltage which is mentioned as Geiger Mode. But how this actually working. When bias voltage aceede breakdown voltage, generally high ...
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I'm a zoology minor and I'm trying to understand electrical gradient. I found this explanation in an authentic website but cannot undertand it fully. An unequal distribution of charges across the ...
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### What is the current in a circuit with two voltage sources in series? [closed]

What happens? We have 2 voltage sources and 2 currents. When I2 and I3 come together (they have opposite sides), what happens? I tried writing down the voltage relations but I'm stuck because I don't ...
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### Relation between Power, Voltage and Current when one or more of them is amplified?

$$\text{Power}(P) = \text{Voltage}(V) \cdot \text{Current}(I)$$ If voltage or current is amplified or multiplied what happens to power and current. Does this affect in increase or decrease in power ...
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### How does voltage produce current?

I am studying electric current and i dont understand how does voltage(potential difference )produce current? PS : I am a 10th grade student so please avoid complicated terminologies.
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### Solar cell efficiency

What is the relation between open circuit voltage and efficiency of the solar cell? Let say that I include the graph of Voc and efficiency in my result. How to relate them both? Thanks :)
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### Transformers and DC voltage

Ok, if I have a transformer with 100 coils of the primary and 200 coils on the secondary and I connect a 9 volt battery to the primary, how many volts should I expect from the secondary coil? I know ...