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).
So I'm confused on a few things about this circuit. I know my math is right (since I got the absolute values correct), but the signs are off since I can't tell when the voltage, current or if the general power equation is positive or negative.
A) So my first question is, where is the current...
Dear PF,
In the figure down below is Q7.47 which asks to determine the voltage v(t) across the capacitor for t > 0.
Since it is given that V(0) = 0 there are two scenario's which is between time interval 0 < t < 1 and t > 1 according to the independent sources.
For the scenario 0 < t < 1 the...
Hello,
I am trying to find base voltage. In attached picture (using Multisim) there are two separate circuits. Here is how I am doing the voltage divider:
Circuit on right:
Vb = (Vcc - .7)*R6/(R6 + R5) = 3.2V which matches Multisim result. No problem here.
Circuit on left:
Vb = (Vcc -...
The question is to find the Hall voltage
The magnetic field is in the +ve Z-direction, the electric field is in the +ve X-direction, the current will be in -ve Y direction.
There are many equations to find the hall voltages ##V_H = Ed=Bvd = \frac{BJd} {\rho w} ##. But i find the equation ##V_H...
Hi everyone,
I'm currently working on the problem listed above.
I'm pretty new to electrodynamics, and I'm learning on my own through a book. I was wondering if someone can please help me through this problem. Here are my thoughts:I think I need to use Faraday's Law of Induction for part (a)...
originally ,I want to prove (TT:current can only flow from c to d),thus I try to figure out what will happen if Vd >Vc,then I label corresponding current direction.Afterwards,I know what's wrong: (A:current doesn't flow out of d ),then I attempted to prove A ,yet I consider that A might not...
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...
Hi
I am completely stumped by this question - I have no idea where I am supposed to start with it. I have the answer to part a), which I had no trouble with.
Part B confuses me as I am not sure what the frequency of operation is. Would someone be able to help me to understand where to start...
Here I disagreed with my professor's solution, so I'd like to check with you guys. Each B4+ ion in a perovskite ABO3 structure is displaced by ##0.2 \mathring{A}## parallel to the ##c##-axis w.r.t. the centroid of the unit cell, after the cubic-tetragonal phase transition below the Curie...
Find the supply voltage of a ladder circuit shown, so that I=7A. Assume R=11Ω. (The unit must be placed)
Hello, everyone. Please, help me with this. Could someone explain to me how to solve such tasks. I literally spent the whole day watching Khan Academy and trying to figure out how to solve...
I would like to ask a question about the induced voltage of an AC generator. So, according to a graph I found on Google, the maximum induced voltage is reached when the loop is parallel to the loop. (The graph shown below.)
Then I was wondering, what if the loop is initially (when it is at 0...
I have defined 5 currents but I can't seem to solve it.
I1+1=I2 (left)
I5+1=I4 (right)
I2+I4=I3 upper node
By KVL I have determined that I2 and I4 are equal, but I cannot determine the specific current across each resistor. Thank you for your valuable help.
Really very elementary one, if i refer the circuit below
For the source in the direction of current the polarity is -Ve to +Ve that is understood which is conventional current, but in the case of resistance in the direction of current the voltage V_R polarity is -Ve to +Ve. Why for resistance...
At first, I started with the result from an earlier problem regarding the capacitance of a cylindrical capacitor:
$$C=\frac{Q}{V}=\frac{2\pi \varepsilon _0\varepsilon _rl}{ln(R_1/R_2)}$$
$$\Rightarrow V=\frac{Qln(R_2/R_1)}{2\pi \varepsilon _0\varepsilon _rl }$$
Then I used the equation...
When the energy of the capacitor is minimal it has no charge therefore the voltage on it is 0. That means that the voltage on the inductor is 0 as well at the moment.
The part that confuses me is: why isn't the correct answer 0? How can a voltage change in a single moment?
Furthermore I am...
Potentials in points E, F, A, B are equal because there is no resistance. In my opinion, losses of potential energy in the resitors R1 and R2 are not equal (potential C ≠ potential G). Then why do we say that voltage in this circuit is the same?
Hi,
I was recently attempting a question about transmission lines and I don't seem to really understand how the voltages travel through the line.
Question:
If we send a voltage pulse of amplitude ## V_0 ## through a lossless transmission line, what does the voltage at the output look like when...
From the ideal diode model, we can derive the open-circuit voltage (Voc) as:
$$ V_{oc} = \frac{nkT}{q} ln(\frac{I_L}{I_0} + 1) $$
where ##I_0## is the dark saturation current and ##I_L## is the light generated current. From the model, if the recombination rate increases, the dark saturation...
If i was conducting an experiment where i wanted to determine the ion selectivity of an ion channel that has a similar structure to voltage gated Na channel but is different in ion selectivity, would i use a voltage clamp or current clamp to figure this out. Also would i use a cell line or an...
I understand that PCB trace spacing is typically based on a minimum found in certain standards and that is voltage based. If the breakdown strength of the dielectric is based on e-field intensity, wouldn't it be beneficial to actually consider the material properties and make it based on a...
I am looking at using a few 2 kV film box capacitors in series and I'm trying to make the board as compact as reliably possible. Let's say that I have two equal valued series capacitors rated for 2 kV each in series across a 4 kV power supply. Each capacitor will then have a voltage at 2 kV...
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...
Could someone please help.
i need to connect a 12vdc motor which can draw 16 amps
to a switch that has an led on it. the led is rated at 3v 20mA.
The power supply i am using is rated to put out 12vdc at 30A
I thought of the possibility of adding a resistor to the positive pole of the led.
In...
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...
In a house (USA) there is "combination switch" ( e.g. https://www.acehardware.com/departments/lighting-and-electrical/switches-outlets-and-plugs/switches/3235199?store=16359 ) containing 2 two-pole switches. [Edit: correction: 2 single pole switches]. The electrical diagram for the circuit...
For Q13 D) E) F), the model I had built was based on elastic collision with the blobs going out of the box, but colliding with air particles and then going back into the box. Thus, momentum would be redirected and it would be higher than what the answer says and kinetic energy would also be...
I had previously solved this using Root Mean Square method by integrating the value of voltage from t=0 to t=T/2 and then from t=T/2 to t=T.Answer was Vo/2½.Yesterday I found this question👇🏾
if I followed the previous approach then:
5 volts is not even in the option. How can I find the DC...
Consider a circuit with a witch, capacitor and an AC voltage source.
The sinusoidal AC voltage source is depicted in the following graph:
We know that, ##Q = CV##
##\frac{dQ}{dt} = C \frac{dV}{dt}##
##i = C\frac{dV}{dt} \tag{1}##
So from the graph, the voltage increases rapidly around ## t =...
From this, I can transform the current source to:
I can then find the equivalent resistance to be (30//20)//40 = 9.23 ohms.
However, I am not sure how to find the equivalent voltage in this case?
What should I do to start?
##V_{BE}## is basically the difference in voltage between the base terminal and the emitter terminal.
Normally when silicon is used and the transistor is biased to operate in the active region, ##V_{BE}## = 0.7 V approximately.
The way I understand this is that for an npn BJT, the applied...
Induced voltage of DC motor isV=Blv where B= phi/S
where S=2*pi*r*l and magnetic flux is phi=B*2*pi*r*l as shown in the picture.
that leads to the equation V=PZ*phi*N/60amy question is, why do we set S=2*pi*r*l
Shouldn't magnetic flux 0 because the magnetic flux of a closed surface is 0...
This is a very confusing situation for me. If the input voltage were constant, then I would be able to understand that by varying load resistance, I can change the current through it, such that the drop across the load = Vz = 6.8V.
But the input voltage is also not constant. So what am I to...
I have created a voltage adder using this circuit where Va and Vb are the input voltages.
And Vout is between the emitter and the resistor. How can I modify it to a voltage substractor?
I want to compute the dc bus voltage using a programming language, but
I doubt the initial value that I should enter. I use the model from this document. This is the explanation about this model
Based on my understanding, ##v## is the grid voltage. This value can change. What is the initial...
I've been researching dielectric breakdown for a while and came across this interesting experiment:
https://tore.tuhh.de/bitstream/11420/1160/1/Size_dependence_of_the_dielectric_breakdown_strength_from_nano_to_millimeter_scale_TUB_Doc_version.pdf
0.3mm of BaTiO3 was placed between two...
Hi, friends,
I have two queries.
I read somewhere that
1. In class B mode higher plate efficiency (tube amp) permits the use of smaller power supplies...and
2.For low level signals a low voltage supply is used, but as the signal level increases, so a high voltage supply is utilised.
Q1. what...
I'm trying to understand the physical reason why when you drive an ideal inductor (no series resistance) with an ideal voltage step input (no series resistance), e.g. some Vin(t) = V0u(t), the output current will be a linear ramp. I can see how to derive this from the inductor equation, v = L...
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...
Known: V source = 30.0 V
, R1 = 15.0 W, R2 = 15.0 W, R3 = 15.0 W
To determine the current, first find the equivalent resistance.
I = Vsource/R and R = RA + RB
= Vsource/RA + RB
30.0 V/15.0 W + 15.0 W + 15.0 W
= 1.5 A
This is as far as I could do the work for this question. I’m having trouble..
Im unsure if I am on the correct track or have gone off on a tangent. Any help or guidance would be appreciated.
CMRR=20log10(Adiff/Acm)
120=20log10(10^5/Acm)
120/20=log10(100,000/Acm)
6=log10(100,000/Acm)
taking antilogs 1,000,000=100,000/Acm
Acm=100,000/1,000,000
Acm=0.1Max amplified...
I know only these relevant equations for power. But here there is a different situation, we have a parallel plates which we don't have to know I current. How should I think of about this? I wonder if it can be thought of a capasitor or something?
Assume that also we know E, B and velocity .
I'm confused as I'm aware speed is directly proportional to the EMF, but is it proportional to the voltage as well? If the speed of a DC generator is halved and everything else is remaining constant the EMF will have so will the output voltage half
All the references I find refer to safely charging lithium cells by a method like this:
https://www.powerstream.com/li.htm
The next page shows the effects on capacity of charging to less than the 4.2 V terminal cell voltage. For example, charging to 4.0 V still provides 73% of the capacity...
While searching for something else, I stumbled upon this https://robu.in/product/voltage-sensor-module/. It is idiotic to buy something like this, because a voltage divider doesn't cost more than a few cents. But what is the metallic circular component in the middle of the sensor? Some kind of...
I feel like i am spinning my wheels at the start here. so I figured that i would start with some type of wire loop that I could change its diameter. This would allow there to be a change in flux through the loop creating a current through the wire. i could then read the current through 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...
Summary:: I say the answer is A because these are reactive components that take and give back energy from the circuit so no voltage drop across the 2- L & C. Please let me know yours thoughts- thanks
Hello I am a newby to electronics taking a class. Please review my thinking on this problem. I...
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...
I am given that all the BJTs are the same.
First of all, when finding node voltages like Vref should I make the node voltage a voltage source first and then do circuit analysis? If so then I would use KVL but that does not give me Vref = 2Vbe.
I do know that Vref = Vb1 = Vb2. What am I doing...