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Questions tagged [voltage]

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

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80
votes
6answers
15k views

Why does public mains power use 50-60 Hz and 100-240 V?

Is there a physical reason behind the frequency and voltage in the mains electricity? I do not want to know why exactly a certain value was chosen; I am rather interested to know why that range/order ...
46
votes
13answers
10k views

What *exactly* is electrical current, voltage, and resistance?

I am taking AP Physics right now (I'm a high school student) and we are learning about circuits, current, resistance, voltage, Ohm's Law, etc. I am looking for exact definitions of what current, ...
40
votes
3answers
12k views

Will the volt, ampere, ohm or other electrical units change on May 20th, 2019? [duplicate]

When watching a video by Veritasium about the SI units redefinition (5:29), a claim that the volt and unit of resistance (presumably the ohm) will change by about 1 part in 10 million caught my ...
37
votes
16answers
97k views

I don't understand what we really mean by voltage drop

This post is my best effort to seek assistance on a topic which is quite vague to me, so that I am struggling to formulate my questions. I hope that someone will be able to figure out what it is I'm ...
34
votes
5answers
3k views

Reversed First Joule's Law : heating a resistor produce voltage?

I was discussing about the theory that claims that "every emitter also behaves like a receptor": Are emitters always receptors? I was brilliantly told that this theory would be false for fluorescent ...
33
votes
3answers
163k views

Why do we use Root Mean Square (RMS) values when talking about AC voltage

What makes it a good idea to use RMS rather than peak values of current and voltage when we talk about or compute with AC signals.
30
votes
6answers
6k views

Could someone intuitively explain to me Ohm's law?

Could someone intuitively explain to me Ohm's law? I understand what voltage is and how it is the electric potential energy and that it is the integral of the electric field strength etc. I also ...
22
votes
11answers
30k views

What is the difference between electric potential, potential difference (PD), voltage and electromotive force (EMF)?

This is a confused part ever since I started learning electricity. What is the difference between electric potential, potential difference (PD), voltage and electromotive force (EMF)? All of them have ...
21
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8answers
9k views

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 ...
20
votes
6answers
8k views

How do electrons “know” to share their voltage between two resistors?

My physics teacher explained the difference between voltage and current using sandwiches. Each person gets a bag full of sandwiches when they pass through the battery. Current = the number of people ...
18
votes
4answers
13k views

Why does vacuum have a nonzero characteristic impedance towards electromagnetic radiation?

On Wikipedia, the impedance of free space $Z_0$ is defined as square root of the ratio of the permeability of free space $\mu_0$ to the permittivity of free space $\epsilon_0$, i.e. $$Z_0 = \sqrt{\...
17
votes
4answers
2k views

Are voltages discrete when we zoom in enough?

Voltages are often thought of as continuous physical quantities. I was wondering whether by zooming in a lot, they are discrete. I feel like the answer to the above question is yes as voltages in the ...
16
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5answers
56k views

What is the difference between a battery and a charged capacitor?

What is the difference between a battery and a charged capacitor? I can see lot of similarities between capacitor and battery. In both these charges are separated and When not connected in a circuit ...
15
votes
5answers
714 views

At an atomic level, what happens when you connect two batteries in series so that their voltages are added?

I can't for the life of me figure this out. I feel like i'm missing some crucial detail about how batteries work. Imagine two batteries connected in series, like this: ...
14
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3answers
114k views

Why do birds sitting on electric wires not get shocked?

When we touch electric wires, we get shocked. Why don't birds sitting on electric wires not get shocked?
13
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5answers
18k views

How can one derive Ohm's Law? [duplicate]

I am looking for the derivation of Ohm's Law, i.e., $V$ is directly proportional to $I$. Can someone help me with it?
13
votes
5answers
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 ...
13
votes
5answers
3k views

Watts vs. volts amperes

What I understand: In simple DC circuits, this is a product of the current and voltage, such that 1 watt = 1 ampere x 1 volt I understand that a watt is a unit of power (change in energy per unit ...
13
votes
6answers
34k views

Why the electric potential of Earth is zero?

For a localized charge distribution the potential is set to zero far away from the charge distribution (at infinity) Now, when grounding a conductor, i.e. connecting it to Earth, it is said that we ...
12
votes
8answers
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 ...
12
votes
5answers
7k views

Why doesn't an electron accelerate in a circuit?

Why don't electrons accelerate when a voltage is applied between two points in in a circuit? All the textbooks I've referred conveyed the meaning that when an electron traveled from negative potential ...
11
votes
7answers
19k views

Difference between current and voltage sources

I am confused about the current and voltage. My intuitive example would be that of a pipe of say water. The diameter of the pipe determines the amount of water flowing per second but the pressure is ...
11
votes
2answers
9k views

How electric currents can flow between 2 points at the same potential?

According to Ohm's law, if there is a potential difference, $V$, across a resistor then there is a current, $I$, flowing through it. Since we assume that points along the connecting wire are at the ...
10
votes
4answers
2k views

How do resistors generate different heat if we make the current fixed and changed the voltage and resistance? Notice the flow of charge is constant

Consider having a circuit which consists of a battery and one resistor. $V = 10$ volts, $R = 5$ ohms, so $I = 2$ Amperes, and $P = 20$ watts. If we double the voltage and resistance, the current ...
10
votes
4answers
2k views

Is potential difference the same across each branch in a parallel circuit under ALL circumstances?

If you place a cell with negligible internal resistance and an EMF of 5V in parallel with 2 resistors, as shown below, each resistor will have a potential difference of 5V across it. However, if you ...
10
votes
3answers
89k views

Current without Voltage and Voltage without Current?

At school I've always learned that you can view Current and Voltage like this: The current is the flow of charge per second and the Voltage is how badly the current 'wants' to flow. But I'm having ...
10
votes
2answers
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 ...
10
votes
1answer
4k views

What maintains constant voltage in a battery?

I know there's lots of questions that address similar situations, (Batteries connected in Parallel, Batteries and fields?, Naive Question About Batteries, and the oft-viewed I don't understand ...
9
votes
5answers
2k views

How can the electric potential be zero at a point where the electric field isn't, if that field can give a test charge kinetic energy?

Say we have 2 charges set up like above. Why is $V_3=0$ ? I can understand mathematically that the scalars fields cancel out, but I don't understand it physically. If I place a positive charge in ...
9
votes
8answers
1k views

Does Ohm's law $V = IR$ mean voltage causes current, or does it just say that voltage and current are related?

I have read that Ohm's law, $V=IR ,$ just means that $V$ is equivalent to $IR ,$ not that voltage is the cause of current. This is similar to the interpretation of Newton's second law, $\mathbf{F} = ...
9
votes
6answers
25k views

Why is electric potential scalar?

I can't conceptually visualize why it would be so. Say you have two point charges of equal charge and a point right in the middle of them. The potential of that charge, mathematically, is proportional ...
9
votes
7answers
98k views

What causes an electric shock - Current or Voltage?

Though voltage and current are two interdependent physical quantity, I would like to know what gives more "shock" to a person - Voltage or Current? In simple words, will it cause more "electric - ...
9
votes
2answers
903 views

Could anyone help explain this current voltage graph for an LED in liquid nitrogen?

I've been doing my coursework investigating LEDs at various temperatures and I've come across an interesting phenomenon which nobody I've asked has been able to explain thoroughly - wheras at room ...
8
votes
6answers
4k views

Potential Nonsense

How is the voltage along the equipotential line between the two equal-opposite charges ZERO? Two common definitions of voltage between points A and B: (1) The net-work per unit charge against the ...
8
votes
4answers
3k views

Contradiction in Ohm's Law and relation $P=VI$

Ohm's law states that  electric current is directly proportional to voltage provided that physical conditions like temperature remain constant i.e. $$V = IR$$ On the other hand, $$\text{Power = ...
8
votes
2answers
7k views

Why is the voltage drop across an ideal wire zero?

I'm having trouble conceptualizing why the voltage drop between two points of an ideal wire (i.e. no resistance) is $0~V$. Using Ohm's Law, the equation is such: $$ V = IR \\ V = I(0~\Omega) \\ V = 0$...
8
votes
3answers
3k views

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 ...
8
votes
5answers
70k views

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 ...
7
votes
5answers
870 views

Difference between ways of transmitting power

There are two ways to transmit the same amount of power, 1 amp at 1 million volts or 1 million amps at 1 volt. Conceptually what is the difference? How can I think about it conceptually? I would ...
7
votes
4answers
2k views

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

I want to ask a question about the figure below. Why the current does not flow from $-Q$ term to $+Q$ term or from a to b since there is a voltage?
7
votes
2answers
3k views

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 ...
7
votes
4answers
46k views

How can you have a negative voltage?

How can you have a negative voltage? I don't really understand the concept of negative voltage, how can it exist?
7
votes
3answers
651 views

Voltage as electromotive “force”

Considering the "water analogy" for electricity, it seems voltage is sort of like gravity: (image source: http://learn.olympiacircuits.com/electricity-flows-like-water.html) Now when water actually ...
7
votes
2answers
2k views

What does a voltmeter actually measure?

For time varying fields (even quasistatic ones) the electric field is given by $${\bf E} = - \nabla \Phi - \frac{\partial {\bf A}}{\partial t}$$ So what does a voltmeter measure? Does it measure a ...
7
votes
1answer
6k views

What creates voltage? What causes electrons to move in a wire?

I was trying to break down how a transistor works to a friend, and I took a moment to think about electric current and voltages. I realised I do not understand where these phenomena come from. I ...
7
votes
3answers
17k views

If the current is increased, is there more charge flowing or is it moving quicker?

Problem Current is the amount of charge that is flowing through a component per unit of time. For a given voltage, Ohm's law tells us that if we increase the resistance, then the current must ...
7
votes
2answers
2k views

Kirchoff's rules and inductance

Can Kirchoff's loop rule be applied in a scenario involving an inductor? Kirchoff's loop rule states that the closed loop integral of E dot dl is equal to zero. But, in a situation with an inductor, a ...
7
votes
1answer
1k views

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 ...
7
votes
1answer
31k views

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 (...
6
votes
3answers
1k views

Why does my measured I-V curve for a film of aluminum suggest high resistance?

I plotted the I-V curve between two points (few microns apart) on a thin aluminum film. I expected this metal to be a conductor and have a much lower resistance, but the slope suggests that it is ...