It's a measure of how much an conductor opposes current flowing through it. It can also refer to a part of a circuit, which has a non-negligible resistance value.
17
votes
2answers
919 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 ...
16
votes
4answers
536 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 ...
12
votes
4answers
535 views
Simple Circuit Question
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 ...
10
votes
2answers
2k 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 ...
9
votes
7answers
2k 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 ...
9
votes
2answers
1k 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 ...
9
votes
1answer
989 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 ...
8
votes
5answers
556 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 ...
8
votes
2answers
520 views
Is this resistor needed in this opamp circuit?
I'm looking at the datasheet of the MCP6241. There's this schematic:
The op-amp has a input bias current of 1 pA, and \$ 10^{ 13}\Omega\$ input impedance. Is resistor Rz still needed then?
7
votes
4answers
537 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 ...
7
votes
2answers
2k 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 ...
6
votes
3answers
339 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.
6
votes
3answers
249 views
Can I use an inductive load in an ATX-to-bench supply project?
I'm doing my second ATX-to-bench supply conversion, and this time, I've decided to follow the "book" and place the correct minimum loads on all the rails instead of merely the 5V rail. This involves ...
6
votes
1answer
211 views
Why do batteries not last as long in a cold environment?
I know that batteries don't lase as long when they are used in a cold environment, but why is that?
For normal conductors resistance decreases as temperature goes down, so shouldn't the internal ...
6
votes
2answers
132 views
Working out thickness of a copper wire
This was one of the questions for the repetition paper before the test.
"A lit light bulb has a resistance of 1320 Ω. It uses tungsten as a filament, and when hot, has a resistivity of 0.92 µΩm. ...
6
votes
1answer
491 views
Requirement to display 3 mm LED by 220 V AC supply
I want to power a single 3 mm LED by a 220V AC source. For this I think I need one LED, one resistor and one capacitor. I don't know the needed resistor value and circuit diagram. The circuit also ...
6
votes
3answers
1k views
What's the best way to plot the “taper” of a potentiometer circuit?
The problem is designing gain/volume/pan/balance/crossfade/mix controls with a smooth "law" or "taper"; the rate at which the audible volume changes as you turn them. (Described in The Secret Life of ...
5
votes
8answers
1k views
How does the electricity “know” the ratio of the resistance in a voltage divider?
I'm having a hard time conceptualizing what/how things are working in a voltage divider setup. I've read a couple other questions/explanations where the answerer has said to "not think about it in ...
5
votes
4answers
308 views
is the resistance in ten meters of copper wire too high to use in a circuit powered by AA batteries?
I have a wireless security system at home, and the wireless node is too far from the receiver. I was thinking that I could splice about 10 extra meters of wire into the existing line to move the node ...
5
votes
3answers
375 views
Calculating Rout of a bjt while using correct RL
I'm studying the notes of my professor of electronics, and I'm noticing an inconsistency of \$R_{L}\:\$ compared to what I've seen around in books and on the web. Here's what is considered ...
5
votes
2answers
88 views
Voltage distribution between components
I often see the same method for computing voltage distribution in electronic circuits implying components whose V-I curves are not trivial.
For example, in a circuit implying a resistor and a LED ...
5
votes
2answers
236 views
What would the current be if I plug an LED into a perfect circuit
If I had an LED that had a forward voltage of 2.2 volts with a forward current of 20mA and I somehow created a battery that was exactly 2.2 volts and I put that LED, and only that LED, on that ...
4
votes
4answers
275 views
More than 2 resistors in parallel
Most people know the formula for the total resistance of parallel resistors:
\$ \dfrac{1}{R_t} = \dfrac{1}{R_1} + \dfrac{1}{R_2} + {}...{} + \dfrac{1}{R_n} \$
If there are only 2 resistors, that can ...
4
votes
4answers
7k 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 ...
4
votes
4answers
1k views
Precise Resistance Measurement Techniques
This question is inspired by some basic questions on resistors I've read here lately.
What's the most accurate/precise technique for measuring the value of a resistor you can think of? What level of ...
4
votes
4answers
580 views
What should I expect the low end of my multimeters resistance measurement range to be?
I have an old Fluke 79-III and I'm trying to check the resistance of some resistors which should be 0.22 Ohms. Unfortunately, they are all reading 0.6 Ohms and so I'm wondering how accurate I should ...
4
votes
6answers
275 views
Would a 100k ohm resistor or motor emit more heat
Would a 100k ohm resistor produce more heat than a motor that had the same resistance?
+|---------(100k ohms)---------|-
+|---------(100k motor)--------|-
Both circuits have the same amount of ...
4
votes
4answers
761 views
Driving LEDs at long distance
I'm looking to drive 52 LEDs (datasheet), around a large inflatable tent. The LEDs have a forward voltage of 3.3V, at a maximum of 20mA.
I'm thinking of using the NXP SAA1064 I²C 16-channel LED ...
4
votes
3answers
188 views
Resistance to Digital converter
I am trying to make a digital ohmmeter on a parallel port interface that can measure resistance with at least 95% accuracy. I have tried a 555 timer monostable assembly which generates a pulse with ...
4
votes
1answer
101 views
What is the origin of the “r” in resistance measurements? [duplicate]
In a post to the diyaudio forums, www.diyaudio.com/forums 67232, I see terminology that are likely to be measurements of resistance: "0r1", "1r0", and "10r". I am thinking the "r" there means a ...
4
votes
1answer
97 views
Can you pass resistance through analog mux?
I have a digital potentiometer that I want to calibrate by sending in my commands and then measuring what the actual resistance is. However, the resistance from the digital pot is (obviously) ...
4
votes
2answers
223 views
Understanding electric power
While in a mood to purchase a Peltier strip, I visited the amazon page which stated the specs of a Peltier thermoelectric cooler, one stated 12 V and 92 W and other one stated 12 V and some 77 W.
As ...
4
votes
1answer
446 views
How to test internal resistance on small lithium polymer cell?
I'm coming from a computer science background, and will be writing some software to automate battery testing. I have background in math, but little to none in physics or electronics. Please consider ...
4
votes
1answer
89 views
Measuring very small changes in resistor network using current source
I am trying measure a very small change in resistance (approximately .400 Ohms), due to the the effects of connecting a large resistance in parallel with a network of smaller resistors essentially ...
4
votes
1answer
274 views
What is the physical meaning of resistance and power ratings of a loudspeaker?
What exactly does it mean when it is specified that internal impedance (or resistance?) of a loudspeaker is 16 \$\Omega\$? Is that ohmic resistance of the copper of its internal winding? Or is it ...
4
votes
1answer
106 views
Transistor terminal impedence?
Can some one explain the concept of transistor terminal impedance? What is it, and why is it important?
Any links to useful notes/resources will also be greatly appreciated.
3
votes
3answers
154 views
What easily acquirable material changes its resistance when heated?
I'm trying to build a Resistance Thermometer that varies current/voltage output when heated. It has to be DYI, I don't want to buy anything done, only something like a light bulb, and this has to be ...
3
votes
3answers
161 views
wirewound adjustable resistor. Something I missed?
I am by no means an expert on electronics, but I thought that I had a fairly good grasp of the basics. That is, until 10 minutes ago.
1 picture ~ 1000 words, so here is what I have:
The yellow wire ...
3
votes
1answer
290 views
Can Resistance of wires be ignored?
I'm trying to calculate the internal resistance of my rechargeable batteries and haven't got a single battery holder so using I am having to using Banana plugs and Crocodile clips for holding my ...
3
votes
2answers
141 views
Mathematical approch to measuring current, voltage and resistance of mixed series and parallel
If there is a circuit like the one below, where all resistors are 1k ohm, how does one determine the currents? The voltage sources are all 10 volts.
The problem I am having is that I do not know if ...
3
votes
3answers
559 views
What is the typical on-resistance of an MCU output?
In my case I am using PIC24F and dsPIC33F microcontrollers, but where is the on-state resistance of an IO port for a PIC stated in the datasheet? I cannot find it anywhere. And how does this apply for ...
3
votes
2answers
222 views
Lengthen a AC to microUSB phone charger cord?
Can I effectively take a 3 ft standard cell phone charger (AC to microUSB, 750 mA at 5V) and lengthen the cord to 6 ft by splicing the cord or am I going to lose something in the mix? Do I need to ...
3
votes
1answer
117 views
At what frequency will the reactance of a 1μF capacitor equal to the resistance of a 2kΩ resistor?
Here is my work:
\$ R = 2000 \Omega\$
\$ X_L = 2 \pi f L = 2 \pi (1 \mu F) f = 6.28\mu F(f)\$
\$f = \dfrac{2000 \Omega}{6.28 \mu F} = 318.471MHz \$
Does this look right to everyone?
3
votes
2answers
1k views
Do transformers use Aluminium windings?
Looking at wikipedia on resistivity I see that, other than gold, aluminium is a close second to Copper.
Do any transformers use aluminium windings ? I'm guessing they would be less expensive to come ...
3
votes
2answers
4k views
5V to 3V, calculate resistor value (or use diode?)
I want to connect this dv motor to the 5V output of an Arduino board. Of course I need to get the 5V down to 3V in order for the motor to function correctly. I've read that I could use a diode with ...
3
votes
1answer
141 views
Find total resistance
The book (Principles of Electric Circuits by Thomas Floyd 9th edition, International edition) says it's 1.955k Ω...
When I calculate I get (R1 || R2) + (R3 || R4) + R5 = 3.38k Ω...
Thanks for any ...
3
votes
1answer
171 views
Can Z (impedance) have an φ of -105°?
Given a simple circuit with one voltage generator and one other circuit element, if these values are given:
U = 200 ∠ -45° V
I = 5 ∠ 60° A
(both values are phasors - I just don't know how to ...
3
votes
2answers
92 views
What impedances do graphics cards expect on H-Sync and V-Sync for VGA monitors?
I have a graphics card for a laptop whose driver kills itself if it runs for longer than two minutes with no external monitor attached. To solve that, I decided to make a sort of dummy plug that would ...
3
votes
1answer
446 views
Zero Cross Detection Circuit for line voltage [duplicate]
Possible Duplicate:
How can I detect a power outage with a microcontroller?
I'm doing some research with the goal of eventually creating a light dimmer controllable from a micro controller. ...
3
votes
1answer
44 views
calculating resistance for LED strips to use as parking lamps and turn signals
I'm installing LED strips in my car's tail lamps to convert it from conventional bulbs to LEDs. I have a understanding of what I'm doing but not the complete knowledge to make the circuit work ...
