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).
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.
1
In recent days I have done a few experiments measuring the current of water as it goes up from 9 volts up to 36 volts, and following Ohms law to convert it to resistance. And I discovered a very interesting trend. In between 9 and 18 volts, there is a massive drop in resistance (by around a...
Voltage SI unit = Volts
Current SI unit = Ampere
Resistance SI unit = Ohm
Ohm's law : V=IR
Did Georg Ohm (German), Ampere (French) & Volta (Italian) collaborated when Ohm came out with this electricity equation with units for voltage, current & resistance as per their surnames?
Credit goes to...
The following is the question and the solution to the question.
I understand the solution to the part where you find the Ceq and derive Qeq from the equation Q = Ceq*V.
However, I do not understand where V1 = V0-V2 come from.
When calculating the minimum voltage, how do you come up with the...
I check the datasheet of LM 319 high speed comparator online. I was wondering if LM 319 can accept negative supply voltage(-10V) and its possible to produce a 10V to -10V square wave which oscillates along origin rather than just 10V to 0v as shown below.
Hİ :) as you know potential difference in point A to B is equal to the battery's voltage and point A's current is equal to point B's current.So current is I=Q/t , there should be equal charge passing through at same time so how could there be potential difference when there is equal amount of...
i just finished some basic concepts about electricity and wanted to confirm if my deduction/understanding is correct: in a simple circuit of let's say a battery and lamp,motor,resistor, the difference between potential of two ends of battery(voltage) say how much potential energy per charge has...
When we connect tungsten filament light bulb to the battery, filament becomes hot due to electrons losing kinetic energy in the electric field inside of conductor. Heat is eventually converted to electromagnetic radiation making light bulb shine. Light energy comes from flow of electrons and...
Preface: I am new to physics and am trying to learn on my own, though I hope to take a class soon. I looked for a forum for beginners but didn't see one, but this seemed to be the closest forum. So I hope I can get some help with my question here. If it is the wrong forum, feel free to...
Imagine the two terminal of a *parallel-plate capacitor* are connected to the two terminal of a battery with electric potential difference #V#. If the capacitance of the capacitor is #C#, and the area of each plate is $A$. In this process would the energy lost by the battery and the stored...
I understand phase voltage (phase to neutral) well, but I'm still confused by what exactly the potential difference is between any 2 phases in 3 phase power. If you were to try to find the potential difference where 2 sine wave phases cross, then at that instantaneous point, the potential...
hi guys i have a conceptual question .As you know equipotential surfaces is one on which all point are the same potential there is no work required to move a charge from one point to the other . So my question is how can we change the locotion of a particle without using any force ?
Hello guys!
I am a student who currently works on a project based on electrical detection and voltage measurement in electrical cables remotly. So in order to accomplish my work, I'm seeki ng for new ways to detect voltage. I already have some ideas such as using magnetic fields or measuring...
A copper wire contains 3.0 *10 ^ 22 number of charges on 1 meter wire. What speed do the electrons move when there is 2 A current in the wire.
t=q/t=3,20*10^3 C/ 2.0 A = 1,5*10^22 s
v= 1m/1,5*10^3s= 6,6*10^-4 m/s
This is the circuit in question.
During lecture, when checking whether this was negative feedback, my instructor said that if the v_out increases, then v- increases as well, which would lead to the next v_out decreasing because v_out = A(v+ - v-). I get how if v- increases the next v_out would...
why does the voltage of the capacitor eventually go to 0 when discharging the capacitor? I heard that's because "current starts flowing when discharging", but how exactly does that lead to V going down? I know that I = C * dV/dt, but that doesn't seem to help me understand why V goes down (which...
I have been trying for a long time to build a costant current source which I know is impossible to keep the current exactly the same but as much as possible. This is what I have done so far:
The operation is very simple . If VCC is increased the VAC is increased a little bit. When VA is...
Having more difficulty understanding the concept, thus I am not showing values.
What is causing me confusion is the line in the middle. The first aR and bR are obviously in parallel, but the second aR and bR confuse me. I tried calculating the equivalent resistance from the first aR and bR and...
I used the potential at the surface of the sphere for my reference point for computing the potential at a point r < R in the sphere. The potential at the surface of the sphere is ## V(R) = k \frac {Q} {R} ##.
To find the potential inside the sphere, I used the Electric field inside of an...
The problem is for a solid sphere uniformly charged with Q and radii R.
First I calculated taked ##V(\infty)=0##, giving me for :
$$
\begin{align*}
V(r)=&\frac{3Q}{8\pi\varepsilon_0 R}-\frac{Q}{8\pi\varepsilon_0 R^3}r^2\qquad\text{if $r<R$}\\
V(r)=&\frac{Q}{4\pi\varepsilon_0 r}\quad\text{if...
Here is a circuit diagram:
.
We have three capacitors, with capacitances ##C_1##, ##C_2## and ##C_3##. Plates are labelled as ##A_1, A_2, A_3 ... A_6##. Point P is connected to the positive terminal of the battery and point N is connected to the negative terminal of the...
Well i don't you to solve the question for me but I want you to clarify the concepts pertaining to this question. My question is how do I write a equation for the circuit since the there is same charge on one of the capacitors. While writing the equation should i put the voltage across the...
In my opinion, the voltage across the C1 should be 9V as the potential on the side of the positive plate of the capacitor should be (15-6)V and on the other be 0V.
Similarly the potential across C2 should be (7-0)V.
Here I'm basically assuming that the voltage at the negative terminals of the...
This is in python:
#ELECTRIC POTENTIAL
from mpl_toolkits.mplot3d import Axes3D
from matplotlib import cm
import numpy as np
import matplotlib.pyplot as plt
dx = 0.1
dy = 0.1
xrange=np.arange(-1,1,dx)
yrange=np.arange(-1,1,dy)
X,Y = np.meshgrid(xrange, yrange)
max_dV = 10e-5
blockRadius = 3...
Hi everyone!
I ask some help in understanding better the concept of voltage. The voltage is a difference in electric potential between two points ##a## and ##b##. It is defined as
However, I'm a bit confused with the use of notation:
- Is ##V_{ab}## the same as ##\Delta{V}##, or rather...
I honestly don't know how to quite even begin this problem.
Looking at Fig 3-2, the slopes of the graphs are 1/R, and hence where the slopes are 0, we have infinite resistance, in which case current wouldn't flow through that resistor and hence simplify the circuit. So I was trying to find...
From the circuit I have:
##-v_b + v_a + V = 0##
##v_b - V = v_a##
##i_1 = (v_b - V)/R_1##
##I + i_2 = i_1##
##(v_b - V)/R_1 = I + v_b/R_2##
From this last equation I get ##v_b = 10.8## and hence ##v_a = 5.8##.
However, apparently that is wrong. (And hence my answers to #2 were all wrong as...
I don't get this. Since we have analyzed the circuit separately for each source, adding them should give me the final values of I1, V2, I2, V1 etc. However, that's not quite true—from cases 1 and 2, I should have I1 = 4 + 5 = 9 mA, but it's 8mA. Hence, I thought that the black box consumes 1mA...
I am having a hard time solving this. Letting \$i\$ be the current flowing into ##R_3##, ##i_1## the current flowing through ##R_1## and ##i_2## the current through ##R_1##—and the node between R3 and R1 be e_1;
Using KVL and KCL, I've managed to find that
##i + I = i_1 + i_2##
Hence...
I have no problem getting the ##R_{TH}## since from the special element's POV, the resistors are in parallel, and that's the answer.
However, I don't really understand how to get ##V_{TH}##.
Ignoring the special element, it seems that I have the resistors in series this time. But I'm not too...
I don't really understand or see the correct way to approach this.
Letting the current in question be ##i_x## (as shown in Fig. 1), and the unknown (changing) resistance be $R_x$, I can write:
##-V_s + R_s i_s + i_x R_x = 0##, and ##R_p i_p = i_x R_x##. Hence we can also write ##-V_s + R_s i_s...
I assume that because there is a resistance, the polarity of the voltage must be the same as the charge flow, and thus the current, in order for energy to flow in the same direction.
For instance, could I use the example of a light bulb (the resistor) plugged into AC lines; we know that if the...
I already found ##I(t)## using Kirchhoff's laws, I got the equation ##V-RI-L\frac{dI}{dt}=0\Rightarrow L\frac{dI}{dt}=V-RI## then I solved the differential equation getting ##I(t)=\frac{V}{R}\left[1-e^{-\frac{R}{L}t}\right]##. My problem is founding the voltage as a function of time ##V(t)##, I...
Hi all. I'll get to the point. I've been interested in electricity since I was in college. Concepts such as current and resistance seemed easy to grasp for me but voltage remains a little bit obscure. It's thanks to this forum (specially forum members Jim Hardy r.i.p and SophieCentaur, sorry if...
Let ##Q## - charge of one of conductor, ##\phi_1## --- potential of charged conductor, ##\phi_2## --- potential of uncharged conductor.
For the charged conductor:
\begin{equation}
\phi_1 = D_{11}Q ,
\end{equation}
for uncharged conductor:
\begin{equation}
\phi_2 = D_{21}Q
\end{equation}
I see that DC power supply have voltage between it's + & - and its 24V.
However, there is no voltage with ground.
I don't understand - if device's "point" has some potential, why doesn't it give some voltage with ground (which has ~0 potential)
I tried this with phoenix contact...
I connected a PVC insulated alligator clip test lead to a 12V (give 20V) DC power supply positive terminal and a multimeter. After that I connected an other one to the multimeter ground, and a third one to the power supply negative terminal. I turned the multimeter to DC V measure mode.
When I...
Hi all
Trying to carry out an experiment and need a high voltage supply
Looking for say upto 40kv dc adjustable generator been looking on the net and only able to find low cost voltage boosters on eBay
Or if anyone know of a good website to try
Any help would be much apreciated
Thanks...Niki
Hi! I've been struggling with this.
Original exercise here: Find the value of Iy when R=0. And the value of Vx when R is infinite.
For the first part of the question I did this since R=0:
I've tried to solve this circuit and I get that Iy and I5 are 0 A, and this can't be possible since Iy...
Homework Statement
Moderators note: link removed. All images should be uploaded to PhysicsForums.
Homework Equations
V=IR
Series in parallel
Series in current
The Attempt at a Solution
I managed to get the current and voltage of R1 and R2. I've been trying to get the next one R3, but...
Homework Statement
L = 20mH = 20 x 10-3 H
i = 40 mA for t≤0
i = A1e-10,000t + A2e-40,000t A for t≥0
The voltage at t=0 is 28 V.
I have to find the equation for the voltage for t>0.
Then I have to find the time when power is zero.
Homework Equations
v(t) = L* di/dt
p(t) = L*i* di/dt
The...
Let's assume a 2:1 transformer which has a 100V Source connected on the primary circuit and has no/negligible resistance, on the secondary circuit a 5 Ohms resistor is connected. Using the 'Impedance Transfer/Reflection' method, the primary circuit would act as if there was a 25 Ohms resistor...
Hi.
The derivation of the capacity of an ideal parallel-plate capacitor is inconsistent: On the one hand, the plates are assumed to be infinitely large to exploit symmetries to compute an expression for the electric field, on the other the area is finite to get a finite expression for the...
<Moderator's note: Moved from a homework forum.>
Calculate the required voltage to produce a electric arc between 2 iron nails (distance: 3cm).
I´ve read in the internet that you need 1 kV per mm. But how can I calculate this value, that I need 1kV per 1mm?
If this is better for the HW section please tell me, sorry about that.
So Voltage is the change in potential. I'm puzzled by how potential in circuits is the same along different points until we reach a resistor - at which point the potential changes. As in, if we take two points before a...