Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [resistance]

A measure of how much a conductor opposes current flowing through it. It can also refer to a part of a circuit, which has a non-negligible resistance value.

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Why am I not dead after repeatedly touching a high-voltage source?

While playing with mosquito racket in my home, I unscrewed the racket and touched the 2 wires with my hands. I felt that my bones were dislocated, I got shocked, but I am not dead. My calculations say that I should die: the output voltage is 5 kV to…
pankaj prasad
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Correct formula for LED current-limiting resistor?

I'm trying to work out what value resistor to use in a LED circuit. The equation I'd use to do this is: $$ R = \frac{V_{cc} - V_f}{I_f} $$ Seems logical, and makes complete sense. The answers to the question How do I calculate the resistor value for…
Jeremy Kerr
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Why does Ohm's law not work for vacuum cleaners?

I have been learning about Ohm's law and testing the resistance across the plug of my household appliances and calculating the current. For example, my kettle was 22 ohms (10.45 amperes) and is protected by a 13 A fuse. This makes sense, and I'm…
Dominic Edwards
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Using a bottle of water as a resistor

Today, while drinking some water from a \$500mL\$ bottle, I started reading the info about the water and found out that the conductivity (\$\sigma\$) at \$25°\$C is \$147.9\mu S/cm\$. So it came to my attention that maybe I could calculate the…
Thiago
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Two black boxes display the same impedance at all frequencies. Which has the single resistor?

Two black boxes display the same impedance at all frequencies. The first contains a single 1 Ohm resistor. Each end is connected to a wire, so that two wires protrude from the box. The second box looks identical from the outside, but inside there…
Paskualino
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Why do we "need" resistors (I understand what they do, just not why...)?

I have always had a basic understanding of electronics. I am now starting to learn a bit more, using an Arduino as a test platform, and I have a question about resistors that I can not seem to solve through research. Why do we use them? I understand…
Louis van Tonder
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Why are lightbulbs considered resistive load?

A lightbulb (a plain old incandescent lamp) is typically brought up as an example of resistive load. Yet the filament is actually made of several feet of very thin wire cleverly coiled to form a filament which is about one inch long. Clearly…
sharptooth
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Resistance Vs Impedance?

What is the difference between the Resistance and Impedance? When we will say it is an Impedance and when we will say it as an Resistance? Can you explain it with diagram (If possible) and real time example. And how the reactances will form in…
Gouse Shaik
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Anti-static bags - safe to support powered circuit boards?

Is it generally safe to rest a low voltage powered up circuit board on an anti-static bag when debugging? A simple meter reading suggests it is a good insulator, but it must conduct to some extent? Ditto on anti-static mat on the workbench
Dirk Bruere
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Why does my 120V 40W lightbulb only have 26 ohms across it?

I thought that if the voltage source is 120V and the lightbulb is 40W then the current would be 1/3 of an ampere meaning that the resistance of the lightbulb would be 360 ohms. But when I checked it with my multimeter, it was only 26 ohms. The…
ratsmisimo
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Why would you short two pins of a potentiometer?

I've found a potentiometer which controls the heat of a cook top. One of the outer pins and the centre pin were shorted with a soldered jumper. Why would someone do that? What does this achieve?
user1937747
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How to make a dummy load of 1000W - 2000W?

I need to check a 48V battery with dummy loads of 1000-2000 watts for 5-10 minutes. Perhaps using Nichrome wire, i can wrap some around a fire brick submerged in plenty of water and adjust the load by changing the length used?
bandybabboon
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Why does water short out PCBs? (i.e. Why doesn't electricity follow the path of least resistance?)

If copper is more conductive than water (at any reasonable PH), submerging copper electronic circuits in should have no effect, as the electricity should continue to follow the path of least resistance (the highly conductive copper PCB paths, for…
Asker
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Does adding thermal relief on PCB increase electrical resistance?

I am just getting started on PCB design (for fun) and came across this term called thermal relief. It increases thermal resistance so the components can be soldered easily. But according to what I have learned, thermal and electrical resistance are…
user2578666
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Is there ever any reason to prefer 5% tolerance resistors over 1%?

I work at an electronics store and the other day a customer came in who was rebuilding a circuit board. I sold him some resistors, but later he came back in wanting to return some of them because they were only 1% tolerance, and he needed 5%. I'm…
Justin Pederson
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