# What is Voltage: Definition and 1000 Discussions

Voltage, electric potential difference, electromotive force (emf), electric pressure or electric tension is the difference in electric potential between two points, which (in a static electric field) is defined as the work needed per unit of charge to move a test charge between the two points. In the International System of Units, the derived unit for voltage (potential difference) is named volt. In SI units, work per unit charge is expressed as joules per coulomb, where 1 volt = 1 joule (of work) per 1 coulomb (of charge). The old SI definition for volt used power and current; starting in 1990, the quantum Hall and Josephson effect were used, and recently (2019) fundamental physical constants have been introduced for the definition of all SI units and derived units. Voltage or electric potential difference is denoted symbolically by ∆V, simplified V, or U, for instance in the context of Ohm's or Kirchhoff's circuit laws.
Electric potential differences between points can be caused physically by electric charge build up or imbalance (eg. well known "static" and electronic capacitor) also by electric current through a magnetic field, and by time-varying magnetic fields (eg. dynamo or generator), or some combination of these three. Additionally on a macroscopic scale potential difference can be caused by electrochemical processes (cells and batteries) and pressure induced piezoelectric effect and heat induced emf across metal junctions. These latter processes at microscopic level have the physical origins previously mentioned. A voltmeter can be used to measure the voltage (or potential difference) between two points in a system; often a common reference potential such as the ground of the system is used as one of the points. A voltage may represent either a source of energy (electromotive force) or lost, used, or stored energy (potential drop).

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1. ### Can the Voltage Across a Capacitor Be Greater Than the Source Voltage in a Series RLC Circuit?

(a) Substituting the values, I get ##X_L=100\ \Omega##, ##X_C=666.67\ \Omega##. From this, I get ##Z=601\ \Omega##, ##I=49.9\ mA## ##V_R=9.98\ V##, ##V_L=4.99\ V##, ##V_C=33.3\ V## (b) It's possible for the voltage amplitude across the capacitor to be greater than the voltage amplitude across...
2. ### What causes voltage between AC Mains phase and me?

So my question is that if i put other lead of multimeter to my hand and other lead to socket 230 phase wire why it shows 150 volts when i stand at floor and 80 volts when i stand at carpet? what causes those voltages? And yes i know doing that could be dangerous. It also shows weird voltage if i...
3. ### The battery voltage drops when fed to the DC booster circuit

I use a 12V battery to power a DC booster circuit. After just a moment, my battery's voltage decreased, causing the booster circuit to also decrease its voltage. Is there any way to make the battery last longer without losing voltage? Thanks
4. ### Capacitor Discharge: Impact of Capacitance on Discharge Intensity

I don't know if the capacitance of a capacitor is large, the capacitor will discharge with greater intensity than other capacitors with the same voltage but smaller capacitance, right? Thanks
5. ### Variable vs constant power supply

I have a CCTV camera using the ordinary 12 volts AC to DC adaptor that has higher voltage (like 15 volt) when there is no load. I decided to buy a Meanwell adaptor but the datasheet (below) I got doesn't give the no load voltage. What do you call power adaptor in which the voltage is higher at...
6. ### Beginner circuits / ↓ the voltage & ↑ the efficiency

So far this is what I have: I have the power source, two triple in a battery case, negative to the T emitter, T output to the (-) of motor, T base through a resistor to the switch, switch to the (+) of motor. I tried wiring the Led to this junction and the switch, but either the motor or the...
7. ### Calculate the resistance to add in parallel to balance this bridge circuit

The reading on the voltmeter is 0. I figure the potential drop through line AB must be the same as the potential drop through AC (since voltmeter is zero). As such, the 10 Ohm resistor has the same as the effective resistance of the parallel branch. 1/10 = 1/8 + 1/R 1/R = -0.025 R = -40 Ohms...
8. ### I Which law defines the AC inducing voltage in the inductor?

If we connect an inductor without ohmic resistance to the alternating voltage source, voltage should induce in the inductor because of the Faraday's law. Voltage is induced by changing magnetic flux through the inductor which is accomplished by alternating current through it. Therefore, in order...
9. ### I How is Potential Difference Created across a Resistor?

In a simple circuit consisted of a battery and a resistor, how is potential difference actually established on the resistor? My understanding is that battery creates the electric field which propagates through space at the speed of light. Resistor is put inside this field and therefore...
10. ### Understanding of Voltage potential

I am bit confused with voltage potential terminology again to basics When it is referred as Voa it is Voltage of "o" wrt "a". Is it correct? But other major question is as per the document I would have written KVL as Voa - I1 * Z = Vn. I am really confused with notation used.
11. ### Electrical Help with detecting current/voltage with a coil and a spinning magnet

Playing around with electricity and magnetism. Well, trying to anyways. Wound some wire up and down the length of a 4" screw several times. Thought when I spun the magnet close to the coil I would get a detectable amount of current on my voltmeter. Anyone know why I'm not reading anything? I...
12. ### Voltage in a simple circuit (MITx 6.002, Circuits and Electronics)

It seems that in this example Joe measured the difference ##V_{1,+}-V_{1,-}=1.4V## and then ##V_{2,+}-V_{2,-}=0.8999999V##. Shouldn't one of these be negative? That is if current is flowing clockwise, then shouldn't we have ##V_{2,+}-V_{2,-}=-0.8999999V##? And if the current is...
13. ### How to demonstrate the linearity of resistance of water vs. test voltage?

Hi I have a question. I am currently in the middle of a uni project where I am discussing electrical safety of water and I want to work out what the current would be at mains electricity voltage. (240V) I have done many calculations and have eventually got values by calculating resistance at low...
14. ### Engineering Calculate the power of the coils in this RLC circuit

So my attempt was I1*jXl1+I2*jXm=I2*(jXl2-jXc2) + I1*jXm because they are parallel so they should have the same voltage. I got I1=-3*I2. I know that J=6-j4 and that J=I1+I2 so I just plugged in what I got and I ended up getting the result for I2 and I1. But they are not correct. Why? I am given...
15. ### Engineering Calculate voltage and temperature for this temperature-dependent resistor

Is my work correct?
16. ### Engineering Calculate voltage and position of the slider

Is my work correct? I got confused whether the current Splits or not, but i decided against it.
17. ### I Electric arc length in relation to voltage

Provided the length of the arc of an electrostatic generator is 7 cm, can we state that its voltage is around 210,000 V? (details as per link below) https://photos.app.goo.gl/MKSpviQwPh9eS5jZ7
18. ### Calculate the voltmeter reading for this circuit with 2 sources and 2 resistors

I find the current first, which is 2 A. Then the voltmeter reading would be 10 V - 1 x 2 = 8 V. But the answer is 12 V. I don't understand why it should be 10 + 1 x 2 = 12 V Thanks
19. ### Precision voltage divider

Hello! I need a voltage divider where the input is between -10 and 10 V and the output is between -4 and 4 V. I would need something with a bandwidth of 1 (maybe even 10) MHz. Can someone recommend me a reliable product (the price plays a role, too, so being cheaper would be also useful)? Thank you!
20. ### I Photoelectric effect: Saturation voltage

Hi, I just got two inquiries: My understanding is that the saturation current is reached when the intensity of light is fixed, when the potential difference is at its positive maximum magnitude. Subsequently, whatever kinetic energy store of any photoelectrons, however deep within the metal's...
21. ### Reducing the voltage from a servo

Hello! I am trying to control a laser frequency (locking it to a cavity) using a servo (implementing a PID loop). The servo can output voltages between -10 V and 10 V while the laser can only take between -4 V and 4 V. What is the best way to make sure that the voltage to the laser stays below 4...
22. ### Converting oscilloscope voltage to laser power

Hello! I have this photodiode which I connect to an oscilloscope using a normal BNC cable to an oscilloscope, terminated with a 50 Ohm resistor. I measure the output from an optical cavity (which is basically laser light), which in my case looks like a flat signal close to zero, and regular...
23. ### Induced voltage in loop with multiple switches

If a current flowing within a loop is interrupted by a switch a spark occurs at some point which is a result of the built up potential across the opening switch contacts due to the stored energy in the magnetic field that was created by the flowing current. But what happens if I have a loop...
24. ### Engineering Derive the governing equation for the voltage Vc across the capacitor

I was thinking about doing KVL around the circuit at the right but I noticed when the switch opens, the current through the circuit at the right is not the same throughout -5 + Ic*2*1-^3 + Ic*10^3 = -Vc Ic is not the same around the right circuit so I am stuck....
25. ### Need a voltage divider for a capacitor source voltage

The end goal is I need to convert a sinusoidal into a square wave using a zero crossing circuit. I have a voltage that ranges from 0 to 400vrms @70kHz from a capacitor that is part of an induction heater tank circuit. My comparator has a peak differential input of +/- 35v so I need to reduce the...
26. ### Calculating electric charge from graph (capacitor)

Apparently, we need to integrate the functions from 0 to the time when it is fully charged. However, I integrated in terms of t so the soultion (according to a graph programme) should be around 236 Vs but I don’t see how this could help me.
27. ### Understanding Voltage Drop in a Circuit

Here is the figure mentioned above. My thinking is that for maximum current, resistance must be minimum. Thus, R1 is not considered which means the voltage drop of R2 is 10V. So, R2 is 1kohm. For minimum, I=2mA, so R1+R2=5kohm, since R2 is 1kohm, R1 must be 4kohm. This is how I deduce. However...
28. ### Voltage Variation w/ Variable Resistor: Correct?

In this figure, I suppose the maximum voltage is when R2=1kohm and the minimum voltage is when R2=0kohm, which means R2 is a variable resistor. Is the way I think is correct or not? Please give me suggestions. Thank you.
29. ### Determine the voltage at each point with respect to ground

This is the figure stated for problem 57.
30. ### The voltage of a voltaic cell

Hello, What is the voltage of a voltaic cell? Some sources claim it's 1.1 V (the difference of potentials of zinc and copper). But I've also seen its being claimed to be 0.76 V (the difference of potentials of zinc and hydrogen). I know that zinc and hydrogen are the ones undergoing redox...
31. ### Inducing Voltage in a Transformer: How Does It Work?

A changing current in a transformer primary produces a changing magnetic field, which induces a voltage in the secondary (correct?), but if no circuits are closed on the secondary, there's no current in the secondary (and therefore primary as well). So how is this voltage induced?
32. ### Engineering How to calculate the interference voltage?

Hello everyone, I have this circuit and I need to determine the interference voltage. I am not sure, where the interference voltage is applied and how to determine it. I think the interference voltage is uv nad my equivalent circuit looks like this: Am I in heading into the right direction...
33. ### Magnitude of the Line Charge Density of a Power Line

Okay so I am a little confused as to where I made a mistake. I couldn't figure out how to program Latex into this website but I attached a file with the work I did and an explanation of my thought process along the way.
34. ### Engineering Phase voltage and Line-Line voltage relation

The below is the diagram i want to find the phase and line-line voltage relation I am finding difficulty in identifying the loop and applying the KVL. One attempt is U_{VA} - U_R - U_L -U_O - U_L - U_R = U_VB U_{VA} - 2(U_R+U_L) = U_VB -> eq1 Is my attempt correct? i am not confident please help.
35. ### I Are voltage and current waves in transmission lines an artifice?

The operation of a transmission line is based on the axial propagation of electromagnetic waves between the two line conductors. However, the study of the transmission lines does not focus on E and B waves but on voltage and current waves. It is considered that there are resistance...
36. ### Discontinuous voltage graph for bullet going through metal coils

For this problem, The solution is, However, dose anybody please know why the graphs for ##V_1## and ##V_2## are discontinuous where they cross the time axis? Many thanks!
37. ### Engineering Voltage and current calculation of circuit

I am trying to find voltages and currents of the below circuit, 3.3 -22000*I2 - 2200(I2-I3) = 0 3.3 -24200*I2 + 2200*I3 = 0 -> eq1 -(10 - I3)*1500 - (I2 - I3)*2200 = 0 -15000 + 1500*I3 - 2200*I2 + 2200*I3=0 -15000 - 2200*I2 + 3700*I3=0 -> eq2 Solving equations 1 and 2 i get I2=0.38 Amps...
38. ### Troubleshooting a Boost Circuit: Voltage Rise & Gate Issues

Hello. I am creating a boost circuit and there is a lot of problems while testing. Before creating circuit i have simulated circuit in modelsim. Problems. 1. Sudden voltage rise from 40% to 50 % dury cycle. ( i am checking each duty cycle ) 2. When applying a gate voltage to mosfet the the...
39. ### How to measure solar panel voltage using arduino?

I would like to make the solar system a bit smarter. The challenge is that the voltage is high (up to 351Vdc) and the solar negative is typically 40-70V UNDER the "system ground". "System ground" is shared among battery negative, charger negative, inverter ground and ground cable digged down...
40. ### Kirchhoff Voltage Rule Problem

I tried doing three loops. For the bottom I did 9-I1(1) + I2(1) - I3(10) -12 = 0, for the upper left corner I did 12 - I2(1)- I2(5) = 0, for the upper right corner I did 9 - I1(1) - I1(8) = 0. I came to I1 =1, I2 =2 and I3 = .2. This was incorrect, I don't think I am summing the currents...
41. ### B Voltage gradient distortion in Copper when part is over a magnet

I am working with HS students on measuring Current Gradients in Copper for their science project " Current Gradients in the human body during surgical cauterization". Next year I was thing of putting a thin sheet of Copper over strong magnets and using the Voltage gradient to draw the Current...
42. ### A Formula for force between two sheets of aluminum foil under voltage

Hi guys, I am struggling to find the answer on Google and at forums. I am experimenting with two sheets of aluminum foil that are separated by a thin plastic foil. In theorie they should be attracted to each other if I connect one foil to power and other to ground of a DC voltage source. I am...
43. ### Why do we have a charge in the denominator of equation for voltage?

Why do we have a charge in the denominator of equations for voltage and el. potential if both voltage and el. potential are not dependent on charge? Is it just because that was the only way to derive the formula for voltage and then we realized we don't need q? U=W/q --> U=eqd/q.
44. ### Estimates of voltage drop with distance in weak electric field

If I resolve the equation in 0, imposing a voltage value of 5 mV, it gives a non real solution, therefore I cannot resolve it for R=1 because I do not know which voltage value to impose. I am sure this is simpler than I am putting it :) thanks for any advice!
45. ### Engineering Why is the output voltage of the subtractor calculated like this?

Hello! Consider this operational amplifier circuit,a subtractor to be more precise I need to find the Ua (output voltage) using superposition; Now I dont have any values given for the resistors but that they are all the same (R1=R2=R3=R4=R5) so I just need to find the expressions.I've tried...
46. ### Engineering Use voltage nodal analysis to solve for the current flowing in this AC circuit

Hi first time using this forum, I have some homework that I am entirely stuck on, can anyone help me with this question? I understand the placement of nodes, and that I need to convert complex numbers, but apart from that I have no idea what direction that I'm supposed to take in this. I don't...
47. ### Finding the Thevenin voltage

Hello I'm trying to solve my homework assignment, I have successfully found the thevenin resistance which is equal to 3.75 but I'm stuck on how to even get started to find the voltage because there are too many components. I have shorted the load resistor which is called RL but there are too...
48. ### B Voltage & Current: Explaining the Basics for Beginners

This is a very basic beginner question but one which confuses me. We are told that voltage = current x resistance but I've also read that we can have a voltage without current. But, if current = zero, then if V = IR, V must be zero. Can someone explain where am I going wrong?
49. ### High voltage transformer windings position

Good morning all! I have a quick question regarding high voltage transformers, can someone explain why we need to put the low voltage winding the closest to the core and the high voltage winding on the "outside"? Have a nice day!
50. ### Resistance of wet sponge with voltage

hi, in recent science projects I have been studying the effect of water on electrical resistance of materials that absorb water such as wood and sponge (the reason for the majority of my weird questions regarding water and electricity). I am calculating resistance by reading the current going...