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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56
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6answers
17k views

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 ...
38
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2answers
20k views

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 ...
37
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8answers
9k views

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 ...
36
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7answers
7k views

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 ...
33
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8answers
3k views

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 ...
30
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2answers
11k views

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 ...
25
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2answers
32k views

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 ...
24
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12answers
17k views

Why do we “need” resistors (I understand what they do, just not why…)? [closed]

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 ...
24
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2answers
4k views

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? ...
23
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10answers
13k views

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 ...
22
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2answers
6k views

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?
22
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4answers
3k views

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 ...
19
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6answers
8k views

How did I survive this shock? [duplicate]

When I was about 10 years old playing with lamps, I accidentally picked up a wire completing a circuit for a lamp plugged into the wall (120 V AC U.S. standard). I'm not sure if it was the hot or ...
19
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5answers
7k views

Side effects of using large resistances

Are there any problems that can be caused by using resistors of large resistances (in the order of megaohms)? I'm designing a feedback network that is just a voltage divider, and I want the feedback ...
19
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6answers
13k views

Resistors with ends of the same colour

I know the values of resistors if they are gold-colored at the end. When both ends are the same, such as brown-o-p-brown and red-x-y-z-red, I am in problems. How to know which side has the last colour ...
18
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8answers
3k views

Why do fuses burn at a specific current?

We usually specify the maximum current that a conductor (such as a fuse) can handle without burning. But doesn't the conductor really fail when a certain amount of energy/heat has been dissipated in ...
18
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12answers
13k views

Does a diode really follow Ohm's Law?

Does a diode really follow Ohm's Law? Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points. Introducing the ...
17
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7answers
7k views

Why can sticking fingers in an electric outlet kill you?

I just wanted to learn some differences between volts, amps, ohms and so forth and came up with this question. If your skin has 100k ohms resistance and the outlet is 220v wouldn't the current flowing ...
17
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3answers
12k views

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 ...
17
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8answers
15k views

How to measure gigaohm resistors?

I've got an issue that appears to be caused by damaged resistors that are either open circuited or of too low a value due to contamination. The problem is that they're gigaohm resistors, so to a ...
17
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4answers
12k views

What does “the resistance looking into” mean?

See this circuit, from Sedra & Smith microelectronics, 6th edition, page 287: It says that the resistance between the gate and source looking into the source is 1/gm, but that the resistance ...
16
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3answers
45k views

Will doubling thinner wire in lieu of thicker wire work?

I've been needing a jumper cable for a while and have plenty of 10 AWG copper wire lying around. From what I've read, 6 AWG wire is recommended for jumper cables. I want to make a 7 foot cable. So, ...
15
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4answers
5k views

Why would you put multiple resistors in line vs one resistor of the same value?

Why would you put multiple resistors in line instead of one resistor that is the same value? In this case, I have a PCB with three 1k ohm resistors. What could be the reason for this instead of just ...
15
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11answers
3k views

Is there a fluctuation effect between heat, resistance and current?

We are told that heat increases a resistor's resistance (or decreases its conductance) and current decreases when resistance is increased. So with less current, less heat would be dissipated, which ...
15
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7answers
5k views

Ohm's law doesn't seem to be working for this electric motor

I'm a beginner in this field so please forgive me if I'm confusing with my question. There is a component that I can't understand with Ohm's law which is a washing machine drain pump. Washing machine ...
15
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2answers
2k views

What is the purpose of wiring pins 2 and 3 of a potentiometer together?

I build a lot of audio devices - amplifiers, effects processors etc. I've been doing it for about a year and learned a lot of principles. However one thing I still don't understand is wiring pots 1 ...
15
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4answers
2k views

How do I calculate the current in parallel branches?

I've been playing around with an Arduino for a while now, and while I know just enough about simple circuits to get little projects up and running, I still don't know enough to figure out what's going ...
14
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3answers
7k views

Why is 10W resistor getting hot with only 6.5W running through it?

I am running about 6.5W though a 10W resistor. The ohm rating is 220 ohms, which is correct for the circuit ohms which is calculated to about 225 ohms. Here is what is running through my 220 ohm 10 ...
14
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2answers
32k views

What is negative Resistance

I have heard some people talk a bit about negative resistance, but I have never really understood it. What is negative resistance?
14
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2answers
1k views

How does static dissipative foam work?

I am planning to build a grip-release sensor using the foam. I'm pretty interested in the way it works. Does the resistance in circuit increase or decrease when force is applied onto it? And this will ...
14
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2answers
2k views

How do you determine the effective resistance of a finite grid of resistors?

Disclaimer: I am a geophysicist with limited electrical engineering background. I am not sure if this problem is incredibly easy, incredibly complex, or completely nonsensical. My goal: Determine the ...
14
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2answers
3k views

How do you calculate the noise of an op-amp circuit?

I think I know how to do this, but you can find a lot of different instructions and calculators online that contradict each other. I have yet to find a clear, concise procedure for calculating the ...
13
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7answers
67k views

If voltage is measured between two points on a wire, with no resistance in between is the voltage zero?

I have a series circuit. Let's say the battery has a potential difference of 10 Volts. On two points of the wire before the current hits any resistors, I attach ...
13
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3answers
3k views

How can I ensure low-resistance ground contacts to an aluminum enclosure?

I am building an electronics project with an aluminum enclosure. I need to ground it—and very well—for human safety. (The system handles 300 A of current, and I want to be sure that if there is an ...
13
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4answers
1k views

Measure diameter of a ball with Arduino

I'm trying to design a hand-held device which would allow to measure the weight and a size of a fruit (orange/apple). For the weight I can use a load cell, but not sure how to measure the diameter. ...
12
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11answers
3k views

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 ...
12
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4answers
60k views

How do I calculate the resistor value for a simple LED circuit?

I have a simple circuit: The max rating (current) of the LED is 30mA. How can I work out what the resistance of the resistor needs to be? By using ohm's law I found it to be \$3V/0.03A = 100 \Omega\$...
12
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3answers
17k views

Why do diodes have a voltage drop?

Is resistance what makes a diode have a voltage drop? Or is it impedence? If it is electrical energy being converted to light, please tell me what this effect is called.
12
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2answers
10k views

Why does a multimeter put more voltage to measure a smaller resistance?

I noticed this behaviour on two different multimeters (different models and brands as well). At first I did not put a multimeter in the way to measure how much voltage changed for the different scales ...
11
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4answers
3k views

High current melting a spanner - what's happening?

Just a couple of guys doing fun things with a DIY low voltage very high current transformer. One of the things is putting a spanner on a brick and touching the two ends with an extremely thick copper ...
11
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7answers
2k views

Is there any difference between transferring DC over one 36 mm² wire or six 6 mm² wires?

I am designing an off-grid DIY solar power site where the distance between the solar panels and inverter is going to be several dozen meters, so I would prefer to put a thicker wire to minimize losses....
11
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5answers
3k views

Why does reflection only applies to transmission lines?

Why does the concept of wave reflection seem to only apply to transmission lines? For example, for a simple circuit with two resistances R1 = 50\$\Omega\$ and R2 = 75\$\Omega\$, is the voltage wave ...
11
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4answers
2k views

Would an electric fence be able to detect being bypassed?

In the Flashpoint episode "The Farm," there's a scene where you can see one of the officers run a jumper cable from one contact on an electric fence to another, then cut the line of the fence (not ...
10
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3answers
2k views

Where did these Ohms come from?

I am new to electronics and am tyring to figure out something that is a bit disturbing to me. I am trying to figure out the amount of resistance I need to put in series before an LED, and the equation ...
10
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3answers
5k views

Under what circumstances would 5V@2.1A be lethal? [closed]

Besides obviously sticking an output of 5V directly to the heart. Are there areas inside the body where resistance in ohms is so low that a 5V electric potential would be fatal? I got into an ...
10
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4answers
5k views

How to know that I am grounded with an anti-static wrist strap?

The resistance of my Belkin anti-static wrist strap shows 0.983, but how do I know that I am grounded by attaching it to computer power supply alone? See the picture below. How do I know if that ...
10
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2answers
1k views

Shunt resistor, what value should I expect when soldering on PCB?

I am using a 10 mohm 1% shunt to measure current via voltage drop. My circuit is on a breadboard... It behaves as if the shunt has a value of ~30-40 mohm instead of 10 mohms. I double checked this ...
10
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2answers
12k views

Internal resistance of batteries?

In one of the answers on this site, I found link to this project. That article mentions internal resistance of batteries and cells. Where can I find data about common ranges of internal resistances ...
10
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2answers
293 views

Calculate sheet resistance in finite element method

I have a simulation with several polygonial mesh cells (Voronoi-mesh) and their centers of gravity \$P_i\$, each with its own electrical potential. Every cell has the same height \$h\$ all over. How ...