# voltage

1. ### Determine the effective current value in the circuit with C and R

Given: U = 220 V f = 50 Hz r = 20 Ohm C = 100 μF Find: I Solution: 1) Xc = 1/(ω*C) = 1/(2*π*f*C) = 1/(2*π*50*10^-4) = 31.83 Ohm 2) R_eq - equivalent resistance R_eq = (r*Xc)/(r+Xc) = (20*31.83)/(20+31.83) = 12.28 Ohm 3) I = U/R_eq = 220/12.28 = 17.9 A True answer given in the textbook is 13 A...
2. ### B Request for historical background on the concept of voltage

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...
3. ### Potentials (and $\Delta\phi$) of nearby converging bodies

Let $Q$ - charge of one of conductor, $\phi_1$ --- potential of charged conductor, $\phi_2$ --- potential of uncharged conductor. For the charged conductor: $$\phi_1 = D_{11}Q ,$$ for uncharged conductor: $$\phi_2 = D_{21}Q$$
4. ### PNP transistor and Voltage

The problem: My attempt:
5. ### Why a DC power supply doesn't have a voltage with respect to ground?

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...
6. ### B Why can an electron go through PVC insulator

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...
7. ### Electrical High voltage DC 30kv - 40kv

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
8. ### Engineering Help me finding the current in here please (Circuit analysis)

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...
9. ### Finding the current and voltage for each resistor

1. Homework Statement Moderators note: link removed. All images should be uploaded to PhysicsForums. 2. Homework Equations V=IR Series in parallel Series in current 3. 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...
10. ### Deriving Voltage from the Inductor Equation

1. 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. 2. Homework Equations v(t) = L* di/dt p(t) = L*i* di/dt...
11. ### B How a Secondary Resistor affects the Transformer Primary Side?

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...
12. ### I How to treat the "ideal" plate capacitor more rigorously?

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...
13. ### B Electric arc: How to calculate the required voltage for a light bow?

<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?
14. ### Puzzled by how the Voltage is the same across different points

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...
15. ### Energy dissipated in the resistors in a 2 mesh RC circuit

1. Homework Statement Hi mates, I have problems solving the third part of this exercise, I've already done all the previous calculations. Given the following circuit, where the switch S is open, the power supply = 50 volts and: The initial charge in the C capacitor: QC = 0 coulombs The...
16. ### How to find power and voltage using the mesh current method?

Hi. I am practising for my test and since I don't have the correct answers, I don't know if what I'm doing is right. I tried to solve this problem, can you check it and correct if it's wrong? Here's a clearer picture of the circuit. I suspect Uab isn't right, but am not sure. Thanks...
17. ### A few questions concerning voltage, current and resistance

[ mentor note: post adjusted to conform to hw template and some spellings fixed ] 1. The Problem I have some few questions that connect voltage, current and resistance. Imagine that we have a circuit that consists of a battery (5V), 2 resistors. Now once we close the circuit, battery would do...
18. ### Voltage and electric field in capacitor

1. We've been given a spherical capacitor with radius of 1 cm for inside electrode and 2 cm for outside electrode. Voltage between electrodes is 360 V and the task is to find largest and smalles electric field strength in capacitor. 2. I'm not sure how voltage given in capacitor works and how...
19. ### I Question on the work done while charging up a capacitor.

So the work done when charging up a capacitor is $dW=VdQ$ However, when we add a charge $dQ$ to the capacitor, $V$ also changes accordingly, so I was wondering why the work done wasn't written as $dW=VdQ+QdV$ (one that also takes into account t he change in $V$). Thanks in advance.
20. ### I What happens to the Electrical Potential the closer we are to a point charge?

So I have been wondering: The potential for a point charge at the origin, is described as: (Using the reference point at infinity): V=1/(4πε) * q/r My question is, what happens to this Potential the closer we are to the point charge, and so the closer we would get, the Potential seems to go...
21. ### I How to intuitively understand Voltage and how to measure it?

I am trying to get a better intuitive understanding of voltage and how it is measured. Here is my understanding: Voltage shows the potential difference between 2 points in a circuit and a higher voltage correlates with a higher electromotive force (emf) that moves the electrons through the...
22. ### I Is voltage an inherent property of a metal at a given temp?

I am trying to gain a very basic understanding of voltage. I understand amps and resistance, but not voltage. I am thinking of a copper wire that is used in a basic electrical circuit to light a light bulb. Is the voltage of this wire an inherent property of copper at a given temperature...
23. ### Charging a low voltage battery with a higher one of same Ah

Let's say both battery have the same charge capacity of 3Ah Battery A has voltage of 3V and B has voltage of 6V. Battery A is completely discharged while B is completely charged. If I charge battery A with battery B, wouldn't B be completely drained because they hold the same amount of charge...
24. ### Connect isolated ground to Earth?

I am currently working on a high power class E amplifier which will sit inside a metal enclosure. It is powered by two power supplies - both are isolated but one of the power supplies is mounted in the same enclosure. The power supply itself is in a metal case and that case is connected to...
25. ### Car reading 17V+ in the battery when running, how to fix?

Hi, I have a 2004 Toyota Matrix with 270 000km. It's working great but today when i started my car the battery was going up to 17.2V (i have a battery voltage reader in the car at all time). It's the first time it went up there, it usually stays in the 13-14V. I know something is wrong and I...
26. ### B Voltage vs charge?

If voltage is the difference in charge between 2 points, then why for a capacitor of a larger area or thinner dielectric cross section, do they say that it can store more charge given the same apppied voltage? Isnt voltage the difference in charge between 2 points? So if you can store more...
27. ### B Is there a relationship between voltage and resistance?

I was getting a bit confused with Ohm's law, and the relationship between the current, resistance and voltage/potential difference? From my understanding, current and voltage both increase or decrease together, while current and resistance do the opposite? I was then wondering if there was any...
28. ### Trajectory of a proton as it moves between the plates

1. Homework Statement 2. Homework Equations What makes the shape circular/ parabolic? what determines the direction? 3. The Attempt at a Solution Because the furthermost plate is positive, the proton would be repelled towards the screen, so i or iii. How do I know the shape?
29. ### Potential Divider Circuit

1. Homework Statement 2. Homework Equations 3. The Attempt at a Solution When we will move the contact X towards P, the potential difference should be maximum across the potential divider. I work out A as my answer but I think it is wrong.
30. ### Voltage, Current, and Resistance Calculations

1. Homework Statement I'm asked to find the voltage, current, and resistance through each resistor in the given circuit. 2. Homework Equations Req for parallel = 1/R1 + 1/R2 + ... Req for series = R1 + R2 + ... 3. The Attempt at a Solution First, I want to find the total resistance in...