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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2answers
371 views

Use battery voltage rating or fully charged voltage?

I am using a 3.7V (18650) battery, but its fully charged voltage is 3.85V. When calculating a resister for an LED circuit, do I use the battery's voltage rating (3.7V) or the fully charged voltage (3....
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3answers
142 views

Which current should I use to determine the Watt?

I am making a heated blanket and I have some troubles to determine the heat that will be generated. Resistance: Let say, I use this heated cable with a resistance of 0.3 Ohms/m*. If I am using 10m ...
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2answers
546 views

Best resistance for RED/BLUE 3 lead LED

I have a project where a PCB has been manufactured with an error, where a 3 lead BI color LED (red/blue) has a single resistor to limit the current for both colors. I can fix this by hacking apart the ...
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2answers
707 views

Finding node voltage of a “Y” resistor network

I am trying to find the voltage at NODE1. My initial approach was to find the current starting from the \$15\$V source then going through \$R_1\$ and \$R_3\$ to ground. Then calculating the current ...
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4answers
80k views

How can a resistor affect current AND potential at the same time?

Though the resistor is always introduced as one of the most simple components it is the one which makes least sense to me. Ohm's law defines the resistance as$$R = \frac{V}{I}$$ this means that the ...
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140 views

Regarding the design of a basic voltage divider

I've just entered the fabulous world of circuitry and was wondering about the design of voltage dividers. I understand their function and formula quit well, but was wondering about the actual ...
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2answers
1k views

How to understand this circuit?

I'm studying about Ohm's Law, and the following problem perplexed me. The answer is \$I_{t} = 11\$mA and \$U_{r} = 41\$V. What I need to find is \$U_{t}\$ and \$I_{t}\$. The only thing I've found so ...
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3answers
217 views

how does ohms law apply in power system

It appears that either all the people over the internet have either not thought about this question or that I am mistaken in my thought somewhere: Confusion appears when I try to apply ohms law to ...
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4answers
7k views

How do current limiting resistors work between ICs?

In a simple battery+resistor circuit with a fixed voltage, the resistance of a series resistor determines the current flowing through it. But what happens if this resistor is placed between two ICs? (...
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6answers
2k views

What's the correct term to describe a conductor which doesn't always obey Ohm's law?

Non-ohmic comes to mind, but that gives an impression that the conductor never satisfies Ohm's law. Is there a better term which describes a conductor which might satisfy Ohm's law at certain voltages ...
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1answer
968 views

Convert transformer resistance data from Watts to Ohm

Short version: How can I convert transformer resistance values from Watts to Ohms? Long version: In PSS/E, transformer resistance can be entered as either per unit values (system base or transformer ...
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2answers
767 views

What determines a load's current requirements?

Apologies if this question has been asked before. I'm sure it has but hard to find as wording of question may not bring up the duplicate question. Let us say we have a 10 ohm resistor as a load. ...
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3answers
1k views

Rule of thumb for LED Ballast Resistor

As well all know, using an LED without some sort of current control is a bad idea. One of the most basic types is a simple Ballast Resistor, paired with Ohm's Law. Based on Vin, Vf, and the desired ...
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4answers
1k views

Ohm's Law and in-series components

I am doing some practice problems based on what I learned today in lecture. However, I am stuck on this problem: ...
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4answers
2k views

Ohm's law clarification

I am slightly confused about Ohm's law. I understand V = IR, and I did a simple experiment on paper. The results are slightly confusing, so I was hoping someone could tell me if I'm right? First, I ...
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1answer
3k views

Connecting a parallel port to an Arduino

This is my first Arduino project and while I remember a (tiny) bit of electronics from school I'm struggling to get this working - in fact I've just fried a parallel port PCI card! I'm looking to ...
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3answers
541 views

Simple Ohm's Law Question

Do I need a resistor if \$\frac{V}{I}=0\$? I am working on a simple circuit of an LED and a buzzer in series where the voltage drop would be 2 and 3 volts, so \$R=\frac{V}{I}=\frac{(5 - (3 + 2))}{I}\...
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5answers
4k views

Ohm's law of a circuit which has both a voltage source and current source

The voltage source has a specific voltage through it regardless of the circuit's current and its resistance while the current source has a specific current through it regardless of the voltage through ...
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3answers
467 views

How to reduce maximum power rating of dishwasher for use with photovoltaics inverter? [closed]

I have a photovoltaic power system and an inverter with an overall power rating of 1500 Watts. I want to connect a dishwasher which consumes 2200 Watts when heating the water. Question: What is the ...
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4answers
342 views

Is Ohm's Law always exactly true even at the microscopic level?

My probability textbook introduction just mentioned that Ohm's Law is not always precisely true at the microscopic level. How is this possible? What is causing this to happen?
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6answers
213 views

Understanding Ohms Law

I have seen ohms law like this V=IR and I=V/R. V=IR tells me when you increase resistance Voltage increases. I=V/R tells me when you increase resistance Current decreases. So if I added a resistor to ...
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6answers
11k views

Why are resistor values constant in the face of changing voltage and current?

Small question, I see that resistors are labeled in certain increments (e.g 5, 10 50 Ohms), although a resistor outside of a circuit is completely without voltage and therefore current. Does this just ...
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5answers
8k views

Darn you V=IR, you are wrong (does V really equal IR?)

Here is my simple reasoning. We apply a potential difference across a resistor. All the electrons begin responding. Since it takes time for electrons to respond, our current is not yet fully ...
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1answer
63 views

Proper resistor for simple circuit

I have a potentially stupid question, but I have no idea how to handle the problem. I want to use 9V battery with a diode that requires 5V. So I need a resistor. How do I find the resistance if (as ...
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7answers
3k views

Batteries have zero voltage

According to Ohm's law V=IR. This means that if the current is zero there is no voltage. Does this mean also that an unplugged battery has zero voltage? Then why does it say otherwise in the package. ...
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2answers
353 views

Ohm's Law for voltage divider

I'm currently working my way through electronics for dummies, where I am shown a simple voltage divider circuit comprising of a 6V battery and 2 resistors, R1 (220 ohm) and R2 (1000 ohm) in series. ...
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2answers
254 views

Non-parallel, non-sequential circuit

This is the circuit: I've simulated it and got a current of 30.76mA at the voltage source (5V). With this I've calculated the total resistance to be 162.5 Ohm. Each resistors is 100 Ohms big. But ...
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1answer
254 views

Understanding current readings from a multimeter

If you couldn't guess, I'm new to electronics. So, I've just received my 3V air pump, it didn't come with any specs, so I'm trying to figure everything out. I hooked it up to a DC variable power ...
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2answers
371 views

Calculate LED current when Vf is greater than source voltage

I'm planning on using an RGB LED in my project. \$V_f\$ is different for each die. My \$V_{cc}\$ is 3V. For the red diode, \$V_f=2V\$ and \$(I_f=20mA)\$, therefore I've calculated: $$R = \frac{3 - ...
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2answers
161 views

Ohm's Law vs. Conservation of Energy Misunderstanding

I am currently misunderstanding the relation between Ohm's Law and the law for conservation of energy. I am referring to the example (in the book "Foundations of Analog and Digital Electronic Circuits"...
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7answers
25k views

Where does U for voltage come from?

I believe in Europe the letter U is commonly used for voltage in (eg.) Ohm's law \$U = I × R \$. I think I understand where the letter V came from, commonly used in North America. But what's the story ...
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5answers
6k views

Is Ohm's Law violating itself?

Consider the following circuit... simulate this circuit – Schematic created using CircuitLab Now suppose the resistor has infinite resistance. Then obviously the current through the resistor ...
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2answers
389 views

Understanding Ohm and Kirchhoff [closed]

I'm a computer programmer by trade who has taken an interest in Arduino with the hopes of eventually producing a particular hardware project that has captured my hobby/side-business interest. I ...
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3answers
8k views

Permanently dimming an incandescent light bulb

I have purchased a nice light bulb with long visible wires/resistors and plugged it in, on the ceiling. It burns too bright without a dimmer and does not look as intended (also the lifespan decreases)....
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2answers
10k views

Creating a specific volt/current “test load”

Working on a complex power supply, but to test its limits I would like to create a set of test loads of specific voltage/current. There are several devices for creating a set load, but they seem to ...
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3answers
1k views

DC-DC Step-Down (buck) converter 5V 10A 50watt, not understand how to size the supply

I have a 5V 10A 50WATT DC step-down converter: http://www.powerstream.com/dc-24V-5V.htm I'm just not understanding how to size the power supply needed to drive this converter at max power. I have an ...
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4answers
4k views

What are the consequences of oversizing resistors?

When building a circuit to power an LED, we use Ohms law to calculate the required resistance, then to calculate the required wattage of the resistor. Suppose this formula dictates a 1/8 W resistor, ...
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5answers
1k views

What is more accurate definition of Ohm's law?

What is more accurate definition of Ohm's law and resistance? is it $$R=\frac {V}{I}$$ or $$R=\frac{dV}{dI}$$ This is doubt that developed in my mind during a class where professor derived power ...
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1answer
164 views

Resistor values for LED

I'm reading this datasheet: http://www.jaycar.co.nz/products_uploaded/ZD0012%20-%20AL-50-30RGBC-C-004.pdf The Preferred Value Series Resistor on this page recommends 510/470/470 Ohms for 12VDC which ...
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1answer
127 views

Weird Voltage measurement problem

I have a DC/DC converter outputting 5.18 VDC @ 25% load (1 Ohm resistor). If I measure the voltage at the green nodes it fails out of tolerance, if I measure the voltage at the red nodes (before the ...
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1answer
6k views

Design of a nichrome heating element - achieving predetermined power dissipation

I want to make a nichrome heating element with 1500 watts of heat being produced while running on 120v AC. This will be part of a air heater as a fan drives air over a circular coil of nichrome wire. ...
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1answer
875 views

joule heating - transmitting power at higher voltages reduces resistive loss?

electrical engineering hopeful here. Can someone explain with math how transmitting power at higher voltages reduces resistive loss? I know Joule's Law Power is proportional to (I^2)*R lets say ...
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4answers
667 views

I do not understand what power actually is

I realize this is probably a super common question, but I have to put it in my own words. I try to understand ohm's law with the water analogy. Two tanks with water, one with a higher level than the ...
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1answer
83 views

How would i go about finding Rl when rl is r3

How would i go about finding Rl :/ I'm so lost iv looked for examples and all they have done is confuse me
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3answers
2k views

Does current source affect flow of current in circuit with a variable resistor?

Suppose you have a current source in series with a resistor R the current through the R resistor would be the current generated by the current source. How would the current through the circuit change ...
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3answers
589 views

Application of Ohm's law / Conservation of Energy

I am taking my first Engineering Electronics class, Engineering Circuits I. I seem to be understanding it, but this one example confuses me somewhat. The simplest manifestation of Ohm's Law (...
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3answers
7k views

Voltage drop measurement result doesn't match my theoretical calculation

I have a \$1.5\Omega\$ resistor and \$8.84V\$ battery. My multimeter tip's resistance is \$0.3\Omega\$. I've tried to compare the calculated voltage drop (which is \$8.84V\$) with the measured value. ...
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2answers
904 views

Why does the voltage changes in this simple circuit?

I'm beginning to learn electronics, and there's something I just can't grasp. I was told that a high resistance in a circuit would lead to a smaller current passing through it, but the voltage would ...
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7answers
3k views

Why does an infinitely decreasing resistance infinitely increase current?

So I have been mulling over Ohm's law for hours today. It makes sense to me that the current gets bigger as voltage rises, since the voltage is supplying more electrons and current is the number of ...
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4answers
56k views

accounting for LED resistance

I'm doing a simple lab (I'm a hobby EE) to reinforce my ohm's law math and learn a little about how to do proper measurements with a multimeter. I have simple circuit with a 2.2k ohm resistor ...