Voltage Definition and 1000 Threads

I read this statement from Lenard Audio. "When a large signal spike is created by un-plugging or plugging in signal leads, or when a pre-amp valve is driven hard into distortion (guitar amps), a large non-symmetrical square wave may cause a temporary DC Voltage to appear across a coupling...

In a transformers output, is it the current that is fixed or the voltage? I have been trying to resisitively heat some tungsten foil and I am stuck at trying to find out the amount of current I need in my transformers output. The problem I am facing is that I know that the tungsten resistivity...

The graph below shows the efficiency of an AIR CORE transformer at different voltages (from MAINS). At low voltages, it has high efficiency and gets lowers because of high magnetising current causing heat loss. But why is it higher at some points again? I do not understand this pattern. Please...

I don't know how to calculate the voltages at the bases of every transistor shown in the lower row of that picture (~3V (2.9..V), ~2V, ~1.8V). Any help would be appreciated! - I'm currently trying to figure that out... The other thing I don't really understand: Why do the transistors in the...

hi, I am looking a derivation of built in voltage, but the only thing I could find is a statement: built in voltage can be derived from band diagram with the Fermi energy constant throughout the device, or from equating the drift current through the junction equal to the diffusion current. I...

Hi. This is a problem from an electronics textbook: The output voltage of a voltage amplifier has been found to decrease by 20% when a load resistance of 1 k is connected. What is the value of the amplifier output resistance? How is there an output voltage without there being a load? 80%...

Hi, I need to calculate the threshold voltage for an op amp circuit. I am given "The maximum output voltage swing of the op-amp is ± 3 V for when the supply is ± 5 V." Would this mean that I should calculate the upper threshold voltage as 8V and the lower threshold at 2V? I have added an...

Homework Statement I'm trying to calculate the voltage drop across a 60uF and a 30uF capacitor in series, powered by 60V. Is the formula for voltage drop across capacitor opposite of the formula for resistor, where resistor is R1=R1/(R1+R2) while capacitor is C1=C2/(C1+C2)? Homework...

I have been having trouble calculating the value of the voltage supply. From what I have learned, to calculate the value, it is V= I x R. I have already calculated the value of R2 as the problem asks, but how do I find the voltage supply if I only know the resistane and the power being...

I know there were previous threads about this but none of these actually pointed out what I am asking for. So if we set the negative terminal in the battery to have 0 potential energy and let's say that Voltage of a battery is 12 volt. So at the positive terminal a one coulomb of charge has 12...

Homework Statement Consider having a battery, its voltage let's say 20 volts. If you connect this battery to a wire. Its resistance is zero. If you precisely measure the voltage at the end of the wire, Would it equal 20 volts or no? Homework Equations dV = I R The Attempt at a Solution Well...

Homework Statement FIGURE 3 (on page 7) shows a PIR (passive infra-red) detector and its associated amplifier, as used in burglar alarm systems1. (a) The detector is powered from a 12 V unregulated supply that needs to be stepped down to 5 V. Design a suitable 12-to-5 V voltage converter using...

First, the electric/Coulomb force set up by a battery across its terminal is conservative, and its potential is given by the well-known V. I also understand the conventional usage of emf is as a voltage potential. However, a battery does more than just set up the electric field and its...

Hi, I have some trouble regarding the relationship between voltage and reactive power. From what I've read you control the amount of reactive power the generator is producing or absorbing by increasing or lowering the excitation of the generator. I have some trouble getting my head around...

HVDC transmission line voltages are usually written as, for example., +/-500kV. Does this mean the voltage between the two conductors is 500kV, or does it mean that one conductor is 500kV above ground and the other is 500kV below ground, which would mean the voltage between the two is 1000kV...

Homework Statement I was looking at a question which asked when the induced current in a circuit was greatest, and this was when the rate of change of magnetic flux was greatest. However, this (seems to )contradicts V = IR. Can anyone explain? Homework EquationsThe Attempt at a Solution

Homework Statement Two identical light bulbs are connected to the ends of the battery. In the first case they are connected in series and in the second they are connected in parallel mode. What is the ratio of the electrical power of light bulbs connected as mentioned? Homework Equations...

This has been confusing me a lot lately. I built a type of battery derived from a solar cell that outputs a constant voltage of 0.5 Volts. My original plan was to work out a method to boost this voltage to around 1V to power a joule thief and light an LED using a capacitor charged by the cell...

I have a 24 volt power supply to power a 12 volt fan. Since I don't want to burn the motor out I used a voltage divider with two 1kΩ resisters to cut the voltage in half. I measured that the voltage on the divider is 12 V, so this is good. However, it won't drive the fan. When I hook the fan...

Homework Statement Find Vth and Zth. frequency = 2kHz Homework Equations w = 2 * (pi) * f ZL = j w L ZC = -j / (w * C) V = I*Z ZR = R The Attempt at a Solution At first I tried using nodal analysis which I receive the value V = 0 v. I believe this is because this circuit only has dependent...

Hello everybody, this is probably a very novice question, but imagine anode and cathode, both made from copper immersed in CuSO4 aqueous solution (1M at standard temp and pressure + assuming electrodes are very near each other -> minimizing diffusion/migration resistance) and: Cu(2+) + 2e- ->...

Problem: my photo diode receives pulses of width 10ns-150ns and repeating at rate of 1Hz-50KHz the current from photo diode depending on incident light can go from 10nA-100mA, in a nutshell, my application tries to digitalize the analog pulses for pulse width measurement so i have 'only' two...

Hi I'm looking for a suitable high voltage prob for my research project. I'm in contact with voltages that can have transient spikes as high as 3.0kV but my DVM only measures up to 1kV and 97% of the time I am under this range. I bought this and it was perfect the only problem is that it has a...

Homework Statement Does hall voltage disappear after the electric force on charge carriers balance the magnetic force? Homework Equations qE=qvB The Attempt at a Solution My understanding: By placing a current-carrying conductor in a uniform magnetic field, magnetic force is exerted on the...

Homework Statement Three resistors are connected as shown in the diagram. If the current from the power supply is 250 mA and the current through R3 is 54 mA, what is the resistance of R3? Homework Equations 1/Req= 1/R1 + 1/R2 +1/R3 V=IR The Attempt at a Solution First I used the parallel...

Please can someone tell me if this calculation is correct? Please see attached question. I have used the +/-3V as the saturation voltage and multiplied it by R2/R2+R3 to give me +/-1.5V.

I know illumination, bandgap of the material, temperature, quantum efficiency all have an effect on the current and voltage of a solar cell. But what about the doping, and the generation and concentration of charge carriers? A semiconductor can only generate a finite number of charge carriers...

Say I had a 10VDC supply and I need around 3.3VDC at 30ma. Let's say the 3.3VDC will power a LED. V1= 10VDC R1= 82 ohms R2= 47 ohms V2= 3.64 VDC from the junction to ground I= 28.24ma...I guess I don't know what effect the LED will have on the circuit and I don't understand how to find the...

What is the effect of on-grid PV systems, in terms of quality, voltage and stability? I'm not really sure how to answer this. Stability -- If consumer is tied to a PV power plant, grid stability could potentially be an issue. However, generally speaking, on-grid systems use the grid like a...

Homework Statement R1 = 2 ohms R2 = 4 ohms R3 = 6 ohms E1 = 10 V E2 = 14 V What is the voltage between point A and B ? A. 0.18 V B. 0.98 V C. 1.34 V D. 1.64 V E. 3.28 V Homework Equations KVL The Attempt at a Solution [/B] I tried using KVL I assume that both mesh currents will go in...

Homework Statement A Primary coil, with ##n_1## turns, is driven with a voltage ##V=V_0sin(wt)## Find the voltage in a secondary coil, with ##n_2## turns, as a function of time Homework EquationsThe Attempt at a Solution Mutual Inductance ##M=\mu_0 n_1 n_2/l *area## ##emf=-d\phi/dt##...

Homework Statement Apply Ohm's law and the nature of parallel circuits to determine the total current in a parallel circuit with three resistors: 3Ω, 6Ω, and 9Ω, respectively. The total voltage in the circuit is 12V. Explain your reasoning. Homework Equations [/B] Ohm's LawThe Attempt at a...

Here's a random thought that I don't as yet have a satisfactory solution: Let's assume we have a copper column resting on an insulated table. Copper is an electric conductor, which means that some electrons within the copper column move freely throughout the column, subject to electromagnetic...

Homework Statement A typical electric blanket consumes 50 W of power when operating. What is the overall resistance of the blanket if it is designed to be plugged into a standard powerpoint? Power = 50 watts Voltage = 240 v (standard powerpoint) Homework Equations I (current) = Voltage/...

1. If e.m.f is NOT a force, but actually energy – and e.m.f is measured in Voltage – then why is p.d. (V) NOT used up? Since we know energy *does* get used up by the component. I know the electrons are just the medium – energy carriers – but Voltage doesn’t mean number of electrons; it means...

Please help! I have recently completed an experiment on transformers, using a step up transformer. I am aware of all the theory that shows that in a step up transformer, the induced voltage should increase and the induced current should decrease. However, in my experiment, my hypothesis is not...

Homework Statement What way does the current flow through the first light-bulb? Homework EquationsThe Attempt at a Solution This isn't really a homework question but related ot my school work. I'm doing Kirchoff's Laws and normally I would have just thought that the current (if we use...

Hello. I have been running several experiments on an electrolytic cell, and I am trying to determine if side products are being formed at higher voltages. My thinking is that once the initial potential barrier is broken, and the resistance stabilizes, a volt vs amperage graph should be linear...

Hi everyone, I am a little confused conceptually about electrostatic voltage and DC voltage. I did my bachelors in biochemistry (where I’m working today), I’m learning/relearning physics as a hobby. I did well in high school physics and first year physics but I’m afraid I’ve forgotten most of...

I need this clarified. I've been told that if you have a circuit with a load resistance of 0, but you have a power supply of internal resistance, when you have no voltage coming from the power pack you will still get a current. I don't understand how this works. I've been told its because the...

Hi. I'm still confused about basic electricity. I have a USB power bank with two 1 A and one 2.1 A outputs. They all are specified with 5 V (all numbers from the manual, not measured myself). I just can't bring this into agreement with Ohm's law U=RI. Shouldn't the resistance R only depend on...

When I connect a AA rechargeable battery directly to a voltmeter, voltage increases slowly, regardless of the way I connect it. I can't figure out why.

Homework Statement I have recently performed an experiment where the voltage drop and current through a diode were measured. I am wondering why the voltage drop across the diode changes. Theoretically, the voltage drop should stay the same as there is a certain amount of energy required to get...

Homework Statement Hey everyone I have a physics e&m question: [/B] http://blob:https%3A//www.physicsforums.com/aa779f37-be23-43d7-a888-d70263a3854b Homework EquationsThe Attempt at a Solution I took the derivative to find the magnitude of the induced voltage. (do I need to add a constant...

I don't understand why the voltage drops only when the charges in an electric circuitnpass through resistors or electric devices, but don't drop as charges move through the wire. As charges move through the wire due to electric potential differences, from a high potential to a low potential...

Hi all, I think I know the answer to this question but I'm having trouble explaining why it is so. If I have a circuit with a fixed resistor connected in parallel with a reverse biased diode, I believe the voltage drop across each will be the same. Is this correct? If so can someone explain the...

Homework Statement When the internal resistance is large in comparison to the external resistance, the terminal potential difference falls to a small value. This is used to make high voltage supplies safe for use in a laboratory. Explain how this makes the supply safe. Homework Equations...

Hello Everyone! So, I need to calculate the voltage in the capacitor, let's call it Vc(t). For t=0- I know that there is no current in the capacitor. Did some calculations and I've found that Vc(0)=6v. Now i need to know Vc(infinite) But when the switch key is opened and the time goes to...

Homework Statement for S1,S2,S3,S4 are all closed at the long time find the current in each resistor Homework EquationsThe Attempt at a Solution why I3 is not = i2? the solution of this question is 24-28I1-I212-12=0 7I1-32=3-----(1) 12-12I2-163=0 3I2+43=3 ---(2) I1+I2-I3=0---(3) I1=0.492...

Homework Statement Homework Equations $$ V=IR $$ The Attempt at a Solution To simplify the algebra it was suggested that I set $$ R_{1}=R_{2}=R $$ and $$C_{1}=C_{2}=C $$ So that's what I did. I labeled the voltage in the middle node as $$ V_{1} $$Taking KCL at the middle node gives $$...