# Questions tagged [voltage]

Voltage, otherwise known as electrical potential difference (denoted ∆V and measured in volts) is the difference in electric potential between two points (adapted from Wikipedia). Voltage can be constant (DC) or varying (AC).

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### Is there any reason why 5 volts is so ubiquitous for powering small consumer electronics?

So pretty much every phone charger, tablet charger outputs 5 volts. 5 volts was part of the original USB specification which I assume had some influence on this, resulting in it just being easier to ...
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### How does a nine volt battery make a spark?

With a nine volt battery, touching the two terminals together (or using a faulty terminal) will cause a spark roughly where I would want it to be. How is this possible? Is it ionizing only a very ...
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### How much time does it take for a switch to go from on to off?

The equation for the voltage across an inductor is v = L di/dt. When a switch changes the circuit from closed to open, it changes the current very quickly. My question is how would one know exactly ...
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### How does data travel inside a wire?

I know this is a very basic question but the answers returned by google are way too complicated for me to understand. I am not asking about modulation here. What I want to know is what exactly is ...
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### What destroys a LED in the reverse direction?

When a LED is included in a circuit that applies a reverse voltage that exceeds the reverse breakdown, a reverse current can flow and the LED might be destroyed. But what is it that actually destroys ...
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### Why does reactive power affect voltage?

Why does reactive power influence the voltage? Suppose you have a (weak) power system with a large reactive load. If you suddenly disconnect the load, you would experience a peak in the voltage. Is ...
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### Why are LEDs in my home unaffected by voltage drop?

As a result of heavy snowfall yesterday night, I woke up to find out that the regular 230 volts delivered to my house had dropped to 110 volts (fixed later that day by the power company). Old ...
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### Why isn't the current split between the transistor and the LED in this NOT transistor circuit?

In the following NOT transistor circuit diagram, the current flows through the 1K resistor and through the LED when the switch is open. This turns the LED on. When the switch is closed, however, the ...
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### Do electrons actually flow when a voltage is applied?

It's said in books that a circuit is a closed path and thus that electrons come back to the source. If that's the case, what would happen when there were an earth fault in a circuit? How would the ...
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### What is CV & CC in power supplies?

In many power supplies, there's CV & CC indicators. What does they mean?
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### Unplugging a router from the wall socket

When the internet appears to have crashed, the service provider invariably gives this advice as a first line remedy: unplug the router from the wall socket, then wait 5 minutes, then plug it back in. ...
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### Combining and Charging multiple Lithium Ion Battery Cells (3.6 V or 3.7 Volts)

1] Voltage: 3.6V or 3.7V Are all 18650 lithium ion battery cells 3.6 or 3.7 voltsor or are there different voltage Lithium Ion cells in the market as well? 2] Possible Voltage Shortage? Do all 3.6/3....
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### Why is mains power sometimes 110V and other times 120V?

(The same question can apply to locations with 220/240V mains, if I am not mistaken.) Frequently I see mixed ratings indicating that something is suitable for 110, 115, 118 or 120V (in the US). I've ...
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### Does the word voltage exist in academic engineering?

In Portuguese, the word voltage does not exist. Neither academic nor technical. In engineering, Portuguese speakers refers to volt as electric tension or potential difference. The word voltage was ...
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### Building an appliance with two plugs to get double the voltage?

I just had a silly discussion with someone about voltages. In Europe the usual voltage is 220 V while in some other places it's 110 V. So we were discussing how to use European devices abroad and my ...
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### Is it normal for DC wall adapter power supplies to provide voltages above the nominal ones?

When I measure a 9V DC wall adapter power supply with a multimeter it shows 11.8V. When connected to my board this voltage lowers to 10V. Is this normal? Should I be afraid of toasting my 1117CD-5.0 ...
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### How can one make an analog voltage memory circuit?

I am looking for a circuit that can, on input, remember a certain voltage and output that voltage indefinitely even after the input has been taken away. The circuit should not change its output until ...
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### Will using a resistor in series with a LED to control its voltage increase the total energy expenditure? [duplicate]

This might sound like a stupid question, but I want a confirmation. I watched a video on Youtube about using LEDs. Those LEDs required a voltage around 2 volts at 20 mA. In order to power one LED ...
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### How does a 24 volt aircraft battery power a 28 volt bus?

Can someone explain to me how a 24 volt battery can power components that advertise requiring 28 volts to operate? The aircraft I fly has a 28 VDC generator that powers both battery and generator ...
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### Does changing the gap between plates change the capacitor voltage?

Consider an ideal capacitor which has a length of $\ell_1$ between its plates. The capacitor terminals are open; they are not connected to any finite valued impedance. Its capacity is $C_1$ and it ...
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### What is the lowest capacitor voltage rating that is safe to use?

I'm using a few Case R tantalum capacitors (10uF 6.3V) as bulk decoupling on the 3.3V power of a 100mbps Ethernet phy. I am also using 0.1uF ceramics closer to the pins. As usual, I'm terribly pushed ...
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### What does it mean when there is a voltage difference between ground and neutral?

Between ground and hot there's approximately 120V as expected. I had expected the voltage difference between ground and neutral to be 0v, but instead it's 0.4V. Why would this not be the case? Is ...
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### I2C: 3.3V and 5V devices without level-shifting on 3.3V-bus?

do I really need a level-shifter if I use 5V-powered devices on an I2C-bus that has pull-ups to 3.3V? In my understanding the devices will only pull the lines (SDA, SCL) low (to ground) and never ...
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### Why isn't there any 9.5 digit multimeter or higher?

Why can't you buy a 91ā2-digit multimeter? Isn't there any need for it? Is a 81ā2-digit multimeter the latest high end you can buy? I have tried Keysight, Keithley, and Fluke, but there is nothing ...
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### Why is there no net current in a wire without a voltage applied?

Atoms of materials with loosely bound outermost electrons constantly exchange charges between each other over time, and these materials are called conductors. Now, the conducting process is different ...
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### Understanding voltage and current

While reading "Electronics for dummies" went through the following block and I realised that I have some uncleared concepts about electricity: Electrostatic discharge involves very high voltages at ...
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### Protect DC Circuit from too much voltage

How do I protect a 3v DC circuit from being damaged, if someone accidentally plugs in a 12v power supply? The circuit will draw much less than 1 amp.
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So the question is as follows: ...
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### Can electronics be damaged by undervolting it?

I was wondering if there are some particularly important mechanism by which one can break electronics, when undervolting it. Its pretty obvious that lots of electronics will not work properly if ...
139k views

### How is it possible to have high voltage and low current? It seems to contradict the relationship between current and voltage in E=IR

I have read different forums and watched a few youtubes (in addition to my textbook readings) and the explanations seem to fall short. The issue seems to be how we are first taught about a direct ...
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### What makes mains voltage safe in homes?

When I started learning about electrical engineering, one of the most important safety guidelines that I learned was that voltages over 36V can be dangerous. As my circuits professor put it, 120VAC ...
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### Does battery voltage actually get lower when connected to a load, or does it just appear to do so?

Sorry if Im wording this question strangely. I am using a 3.7V battery and my microcontroller monitors the voltage and goes to sleep if my battery voltage is too low. The issue is that it reads a ...
34k views

### What is a load resistor?

I am not able to understand what a load resistor is and how does it relate with a load. Can anyone explain how the load resistor works and how is it different from the general resistor.
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### What is the physical meaning of negative resistance?

I am a bit confused about the physical meaning of negative resistance. Mathematically, a component which has negative resistance shows a decreasing voltage across its terminal when the current inside ...
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### Why to disconnect the negative/ground terminal, not positive?

To break off any circuit, the common way is to disconnect the negative and or ground terminal. I rarely see people disconnecting the positive and if so, they're not well educated in electrical ...
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### Reducing 12V to 5V

DISCLAIMER: I know nothing of electrical engineering I just seen this as the best fit category for my question. I have a solar panel that is being run to a controller switch (for lack of a better ...
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### How to name what this resistor is doing?

I have a basic circuit that uses a photoresistor powered by a five volt source. I had made this project to show my son about various sensors and had used a circuit I had found online. It looks ...
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### Voltage is reduced across chained breadboards

My Arduino is connected to the first breadboard. From there, I chained the positive and negative to the other boards. I have 6 breadboards connected right now. In the first board I see (with a meter) ...
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### if a standard three-phase 400V AC connection is rectified what DC voltage comes out of it?

If a standard (in Europe and a large part of the world except North America and Japan) three-phase 400V AC (three lines having 230V RMS voltage if measured to neutral each) mains supply is rectified ...
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### What, exactly, is voltage?

I'm 15 and recently started electronics and I'm having trouble understanding voltage. I've read so many articles and watched so many videos about voltage and they all give different answers. Some of ...