# Questions tagged [ohms-law]

A well known relationship that describes the relationship between Voltage and current through a device's resistance expressed mathematically as V= IR. This formula says that voltage across the device is equal to the current through the device multiplied by the resistance.

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### Ohms law and voltage

So Ohm's law says I=V/R pretty simple, say I had a 5 volt source and a load I wanted to limit to 20 mA, so I would use a 250 ohm resistor which would limit the current to 20 mA at 5 volts. (I'm ...
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### Wattage of DC device is not equal to AC [closed]

I have a led driver (LPC-20-700) that is 30V and 700mA, which makes it 21W. I run 10 leds (≈ 2.8V drop) in series with it and it is an constant current device. If I plug my multimeter between, I do ...
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### Why is my circuit's current far lower than expected with 2.6v / 220Ohm / and LED?

I have a very simple circuit which I have measured the current to be only 3mA but should be in the range of 18mA. I have a simple circuit using 2 AA batteries (NiMH) at 1.3V each in series for a total ...
854 views

### led resistor calculation, and resistor wattage?

I know this has been asked time and time again but bear with me as I am struggling to understand, so say I have this simple circuit here with 120v (dc for simplicity) as the input voltage and I have ...
2k views

### How do resistors limit current for an LED? [closed]

If I have an LED with Vf = 2.1V and I = 20mA, Ohm's Law says I should have a resistor in series at a value of R = 145Ω, if the voltage supply is Vs = 5V. However, I believe can put a higher valued ...
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### Calculating resistance when ohm law has no response

I have a 3v DC source and a 3v light emitted diode, i want power this led with just 5 mA . There is a formula : R = V/I But in my case V is 0 V[source] - V[LED] = 0 So R is 0 always!!! How can i ...
2k views

### Does resistance of carbon brushes in DC Motors decreases after couple of uses?

I know that after couple of uses DC Motors we should replace carbon brush because the physical size of carbon brush will be reduced and it can not do its job! But let me ask my 3 main questions.... ...
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### Add a LED and a resistor to a working circuit

We found, with my 6 y.o. kid, a 9V battery and an old CPU fan power supply fan, and we were happy to see the following circuit 1. working. Then he asked: "Can we add a switch and a LED?" For sure we ...
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### How do voltages at outputs drop as current increases?

As I looked at some 74xxTxx ICs, such as this simple NAND gate, I noticed that the minimum $V_{OH}$ decrease as current flowing from the outputs increase. But, from my understanding of Ohm's law, \\$...
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### General definiton of Ohm's law

There has been some disagreement lately on whether a diode follows Ohm's law or not: Does a diode really follow Ohm's Law? Specifically things like However, the truth is the resistance of a ...
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### 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 ...
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### Is my wire rated at a high enough current?

I am in the process of planning a speaker build. I am making sure my current wiring is up to the demands of a new system. The amplifier is a CV 1800, which can put out 9.5 amps at 4 ohms in stereo (...
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### Why doesn't current increases when the voltage is increased

When connecting two batteries in series the voltage is increased. For example: Connecting two 5V batteries in series will produce 10V voltage but the current will be the same. According to Ohm's Law <...
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### Solving a circuit with node voltage method

I have the following circuit: Knowns: Iz = 80 mA R1 = 100 Ohms R2 = 150 Ohms R3 = 220 Ohms R4 = 330 Ohms R5 = 100 Ohms As I understand Gi stand for the current source internal conductivity, but ...
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### Joule–Lenz Law.. Forgotten history? [closed]

We are all, or should be, extremely familiar with this graphic. It is course the magic triangle used to represent Ohm's Law. We should all also be very familiar with the similar power triangle. ...
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### Do I need a resistor between my battery and servo?

I'm trying to better understand Ohm's law as it relates to general microelectronics projects by taking a simple project I'm working on now. I have a 9V battery powering a small tower pro sg90 servo. ...
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### How to calculate current on different resistors

I hope this is not a wrong place to ask. I've just started studying electrical engineering and I have (a newbie) question and would really appreciate it if you guys could help me. So I have this ...
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### How can 4 resistors of 30ohms each be connected so you end up with a resistance of 18ohms?

An association of 4 resistors of 30ohms each, how can one assemble them so you get a resistance equivalent of 18ohms?
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### Using Nodal Analysis Method

Question: I had solved easier circuits problem using nodal analysis but this one it has supernodes on nodes 2 and 3 which I find it difficult solving. thus I need help as I am trying my very best to ...
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### Why the resistors needs higher Ampers if the Total current is 4 Ampers?

I have a question about the circuit as shown up. My question is if the total current is 4 Amperes, why do the resistors need a higher current? Am I missing something? If that so, what it is?
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### If the voltage at ground is 0, why is there current flow?

From what I understand, voltage is required to motivate electrons to flow through a circuit. With KVL we have that the voltage will essentially be depleted at the return point (ground). So, if this is ...
14k views

### Does a generator produce voltage or current?

I know that this question might sound very stupid for +90% of you, but my brain doesn't really get the electricity generation. The thing that I don't understand is what does a generator produce, ...
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### Why voltage is the same after placing a resistor?

simulate this circuit – Schematic created using CircuitLab Hi. I'm testing a very simple circuit with a multimeter. In Ohm's Law, a resistor should affect the voltage, but in my circuit it ...
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### How many amperes without resistance?

For the below circuit according to Ohm's law the led will get 23mA. What happens if the resistance is removed? How many amperes will the LED get? My assumption is that the wire has some kind of ...
806 views

### Current Flow into MCU pin

If I have an MCU, e.g. ATTiny85, and I connect a 5V source to a pin on the ...
3k views

### Calculating current in a series circuit

Given the following circuit, it seems like we could use ohms law to conclude that current = voltage / resistance. With a source voltage of 3.3 and a resistance value of 220, current = 3.3 / 220 = .015 ...
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### Finding the heat dissipation but calculations not going right?

I am trying to find the heat dissipation from a 20000 V 1 A filament which is on for 1 second. I just randomly came up with this to try to test my understanding of joules first law and ohms law with ...
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### Powering a 5v relay from a 12v power supply

I have a relay which is rated for 5v. My power supply is 12v. I have measured the resistance across the coil as 400 ohm. If I place the relay in series with a resistor that is 560 ohm, would it ...
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### Three series LEDs on 5 V?

I'm new to electronics and Arduino. I bought the Arduino starter pack and I did the first exercise: connect a LED and a resistor. But after I tried to connect more LEDs, and when I connect 3 LEDs ...
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### Why don't we use low voltage Power Sources for high wattage applications?

Super nooby question involving Ohm's law, but this has been on mind this morning. Say I have a 60W device, and I want to power it. Usually this calls for a 120V source or something. However, why not ...
299 views

### How are voltage dividers useful? I can't seem to get enough current for them to be useful

I must be doing something wrong here, because when I make my simple voltage dividers and do the math, the most current I could draw through my voltage divider would be 33.3mA. Here are my factors: ...
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### Reason for inconsistency with Ohm's Law, of current measurements in resistor connected to battery circuit?

simulate this circuit – Schematic created using CircuitLab Connecting various resistors to the same two batteries rated 1.5 V and 9 V as shown in schematic above returns unexpected results: ...
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### Is current calculation in copper wire for AC simple or not?

I'm trying to learn electronics by myself, and I'm starting with simple current calculations. Let's assume we have a straight wire of length L connecting a source and a sink. I know the voltage (V), ...
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### How does electrolytic capacitors work?

Basically I am interested about the polarity of an electrolytic capacitor.How is the polarity of an electrolytic capacitor is defined and what if I reverse the polarity in a simple circuit containing ...
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### Convert 24 V to 20 mA (none is variable)

I have a PLC (take the "P" with a pinch of salt), it has some analogue inputs (4-20 mA) that I need to use to detect if 24 V is present or not. I can program the logic to say above X mA 24 V must be ...
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### High voltage transmission, transformers and Ohm's law

I have difficulties with understanding high voltage transmission and transformers working process. Particularly with this expression: "the higher the transmission line voltage, the smaller the current"...
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### Would lower current cause a battery to go flat slower?

So I understand the basics of ohm's law and batteries. The electrons move from the cathode to the anode via the circuit and when the anode and the cathode have the same amount of electrons they stop ...
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### Struggling to understand series connections based on experiment

I'm having some issues understanding how series connections work based on an experiment I did at school. I took two lamps, and then connected them in series so the power initially goes to the first ...
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### Understanding equilibrium equations

I initially asked this question on math.stackexchange.com, but nobody answer so I thought I could try to ask here, this at least to some degree related to electrical engineering. Please help me to ...
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### Will the bright of the bulb increase or still the same in this simple circuit?

If Lamp2 is disconnected, What will happen to the brightness of the Lamp3? I think that the brightness will remain the same because Lamp2 is in parallel with the branch that contains Lamp3. Let's ...
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### Help understanding circuit with diodes in it

I'm having trouble figuring out how this circuit works in the real world. I know theoretically the diodes should have a resistance of 0, 0 and infinite respectively, which makes the question quite ...
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### 12V DC LED and motor circuit - overheating

I'm trying to build a model lighthouse (don't ask). :-) Essentially I'm trying to have an über-bright LED with a motor rotating at 2rpm, both powered from the mains (120V AC). The problem I am ...
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### Ohms law and a resistor

I've recently just learned from the Internet that a resistor reduce current. But when I measured the amps from the power supple to the resistor in series and then measured again from resistor to an ...
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### Finding the voltage of a circuit composed of a series and parallel?

I was watching a youtube tutorial to understand calculations using ohm's law and I thought I had it down when I ran into this problem: I was asked to find the voltage at points A and B. I was also ...
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### Mesh-Analysis, Ohm's Law & Passive Sign Convention

I am using Fundaments of Electric Circuits 5ed and I have a few questions about Passive Sign Convention with respect to Ohm's Law & PSC FYI passive sign current (PSC) is based on this diagram: ...
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### Application of Ohm's law to a single resistor and to a series circuit

For any given resistor following Ohm's law say a carbon resistor, it's resistance is independent of the value of current and voltage. However, say we had a 5 ohm resistor in a circuit with a 10V ...
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### Why would venting an engine create a negative amperage on a generator?

I'm writing simulation software for a civilian helicopter. The helicopter has two engines and two generators. Normally, we calculate the amperage reading of a generator through Ohms. I = W / V. ...
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### Quick Question about ohms law and resistors

This may have been asked before, but I'm currently I'm an argument about whether or not passing 12v through a .1 ohm resistor would result in 120 amps due to Ohm's Law. (I=V/R) Providing that the ...