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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LED strip built-in resistors too large?

I began officially studying Lessons in Electronics and as practice, I decided to detail an LED strip I've been using around the house. My results raised some questions around the LED voltages on the ...
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What is a multimeter at its core?

We know that, thanks to Ohm's Law: If you have an ammeter, you can put it in series with a resistor of known (usually large) value and now you have a voltmeter (after rescaling ofc). If you have a ...
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Finding the "drop in potential" as current moves through a single resistor of a circuit with parallel resistors

I have four different resistors connected in parallel to a \$24.0 \ \text{V}\$ battery with internal resistance of \$0.500 \ \Omega\$. The resistor values are \$10.0 \ \Omega\$,\$15.0 \ \Omega\$, \$30....
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Finding the voltage available at the terminals of the battery in a circuit with parallel resistors

I have four different resistors connected in parallel to a \$24.0 \ \text{V}\$ battery with internal resistance of \$0.500 \ \Omega\$. The resistor values are \$10.0 \ \Omega\$,\$15.0 \ \Omega\$, \$30....
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Finding resistance for parallel resistors: how is my reasoning incorrect, and what is the correct reasoning?

I have the following circuit: The voltmeter \$V_1\$ measures the voltage drop across the \$9.00 \ \Omega\$ resistor and has a reading of \$4.50 \ \text{V}\$. The reading on ammeter \$A_1\$ is \$I_1 =...
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Calculating the reading on ammeter \$A_1\$: why am I incorrect?

I have the following circuit: The voltmeter \$V_1\$ measures the voltage drop across the \$9.00 \ \Omega\$ resistor and has a reading of \$4.50 \ \text{V}\$. I am trying to calculate the reading on ...
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0 current in a circuit using tunnel diode

Suppose we have a diode with negative differential resistance of -40 ohm in the region of 0.3-0.5 V and we put it in parallel with a 40 ohm resistor: simulate this circuit – Schematic created ...
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Double loop, double voltage source circuit analysis problem, with three unknown voltages/currents, using Kirchhoff's laws and Ohm's law [Post #2]

I recently asked this question: Find the currents and voltages in the circuit shown in Fig. 2.28. Answer: \$v_1 = 6 \ \text{V}\$, \$v_2 = 4 \ \text{V}\$, \$v_3 = 10 \ \text{V}\$, \$i_1 = 3 \ \text{A}...
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Why does a 12V, .5 AMP fan work in a PSU but a 12V, .125A does not? (both are three wire fans)

Completely new to electronics and I'm learning by trying to replace a bad PSU fan (bad bearing but no power problems to the fan). The original fan was 12V, .5A. I bought a rinky dink fan that was too ...
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Computing voltages over resistors [closed]

How do you use the combine/redraw method to find the voltages of the different resistors?
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Double loop, double voltage source circuit analysis problem, with three unknown voltages/currents, using Kirchhoff's laws and Ohm's law

I'm currently studying the textbook Fundamentals of Electric Circuits, 7th edition, by Charles Alexander and Matthew Sadiku. Chapter 2.4 Kirchhoff's Laws has the following practice problem: Find the ...
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Calculating voltages around circuit by using Kirchhoff's voltage law and Ohm's law

I'm currently studying the textbook Fundamentals of Electric Circuits, 7th edition, by Charles Alexander and Matthew Sadiku. Chapter 2.4 Kirchhoff's Laws has the following practice problem: Find \$...
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Why can we say \$F=\phi R=NI=HL\$ according to \$V=IR\$?

Magnetomotive force is a quantity appearing in the equation for the magnetic flux in a magnetic circuit,this is the explanation of Magnetomotive force from WIKI : https://en.wikipedia.org/wiki/...
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-1 votes
4 answers
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In a basic Ohm's Law circuit, is the effect of the resistor localized?

Elaborate way to put my question: Why is the current before the resistor and after the resistor same? Since I'm taking beginner taking classes about electricity, this is what I know about circuits. ...
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3 answers
134 views

How does high voltage increase power without changing current? [closed]

I am trying to understand the application of high voltage in electric vehicles in order to increase power vs using high current. I understand the Ohms law equation P = I x V but I'm just wondering how ...
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Struggling to design R2 to simple circuit specifiations

I have set up a nodal equation such that all currents are entering the center node (\$V_x\$): $$\frac{V_1-V_x}{R_1} + \frac{V_2-V_x}{R_2} + \frac{V_3-V_x}{R_3} = 0 \to \frac{V_1-V_x}{R_1} + I_2 + \...
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2 votes
1 answer
78 views

Finding the mathematical function that describes voltage across diode and resistor circuit

I have the following circuit: simulate this circuit – Schematic created using CircuitLab Where \$\text{V}_\text{i}\left(t\right)=\hat{\text{u}}\sin\left(\omega t+\varphi\right)\$ and the ...
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Voltage drop on resistor with MOSFET configuration circuit [closed]

I have big misunderstanding in calculating voltage and current across resistor in next circuit. I think picture well represent my question. The amplitude of V1 is 3.3 V.
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5 answers
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Heating a very short piece of NiCr wire (0.005 ohms)

How do I generate less than 0.05 V to heat a NiCr wire, or otherwise prevent the wire from consuming too much power? I want to heat a length of Nichrome wire in order to cut through very thin pieces ...
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The sign on each voltage is the polarity of the terminal encountered first as we travel around the loop?

I'm currently studying the textbook Fundamentals of Electric Circuits, 7th edition, by Charles Alexander and Matthew Sadiku. Chapter 2.4 Kirchhoff's Laws says the following: Kirchhoff's voltage law (...
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4 votes
6 answers
863 views

Does a voltage drop exist in a current-carrying loop of wire?

Suppose current is induced in a loop of wire by a changing magnetic flux, would there be a voltage drop along the wire? If a voltage drop does exist then somewhere along the length of the wire there ...
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4 answers
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Physical circuit not drawing as much current as my calculations show

I've created the circuit below and have calculated the following values: R' (equivalent resistance of entire circuit) = 1 / ((1/470) + (1/470) + (1/470)) = 157 ohms I1 = VBattery / R1' = 6V / 157 ...
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How to measure current flowing in each resistor in parallel circuit on Tinkercad?

I have designed a parallel circuit on Tinkercad and I wish to measure the current flowing through each resistor using multimeter. However, the multimeters' arrangement are seemed to be weird because I ...
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2 answers
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Optimal LDA210 optocoupler circuit for mains detection

I am trying to sense mains with an ESP32. For that I plan to use this circuit: I want to optimize the resistors from If current in order to lower the power (W) they use so they don't get hot. ...
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4 votes
3 answers
817 views

Mistake in using KVL and KCL in ideal opamp-circuit

I have the following circuit: simulate this circuit – Schematic created using CircuitLab And I used KCL and KVL to write the following sets of equations: $$ \begin{cases} \text{I}_0=\text{I}_1+\...
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Maxwell equation

$$ J = \sigma E - \frac{dD}{dt} $$ I am having difficulties understanding this equation. I know that \$\small J = \sigma E\$ in the equation is a form of Ohm's law, but what is the other part?
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3 votes
6 answers
2k views

Why do resistors "draw" current? [closed]

I was looking at an explanation for why parallel resistors have less resistance: Resistors in Parallel One of the answers involved simulating parallel resistors as a black box and it made sense. If ...
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Is it true that not all components obey Ohm's law?

After explaining Ohm's law to someone who knew nothing about electronics, I was corrected by another guy, pointing out that not all components obey Ohm's law. I replied with the usual "I know, ...
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If all the resistances inside a passive resistive network is multiplied by some factor, what will happen to the thevenin resistance?

Lets imagine an arbitrary passive resistive network, a black box. Let its Thevenin equivalent resistance across some terminals \$a,b\$ of the network be \$R_{th}\$ ohms. Now lets imagine another ...
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1 answer
192 views

Is there any small and more efficient alternative to a resistor to bring voltage down?

I am trying to sense mains to detect if some LED bulbs are ON or OFF. For that I am using HCPL-3700 (datasheet) that requires (two) resistors to reduce the voltage. This is my schematic: If my ...
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3 answers
112 views

Do I need an LED driver for my application?

My LED has a forward voltage of 17.2V and a current of 700mA at 85 degrees C. I'm using a heat sink on the LED so thermal effects can be ignored. To power my circuit, I'm using an AC/DC wall mount ...
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2 votes
2 answers
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Voltage of IN pin of voltage regulator

A voltage regulator has a constant output voltage regardless of the load so it can been seen as a voltage dependent resistance but I am wondering what will happen in this case: simulate this circuit &...
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3 answers
73 views

Clarification: the role of resistance in producing heat / light (e.g. incandescent lightbulb)

I'm reading Code: The Hidden Language of Computer Software to get a better understanding of what makes a computer work. Early on there is some elementary explanation of what electricity is, and how we ...
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4 answers
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Explain how Ohm's law applies in this tiny circuit

This is a circuit from a tutorial I found on the internet, which is apparently correct. R equals 183.3 ohms as the LED requires 30mA. So the voltage drop accross the R is 5.5 V. I browsed quite a lot ...
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Explain this tiny circuit (2 LEDs in parallel)

Please excuse my schematic. This is a tiny PCB near the DC5.5 Jack port of a laptop power supply. The transformer is broken so I dismantled it to learn some. The transformer reads like "220VAC ...
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1 answer
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Derivation of microscopic Ohm's law from macroscopic version?

What I tried was: $$\overrightarrow{E}= - \triangledown V \qquad \qquad\qquad\qquad (1) $$ $$V= IR\qquad \qquad\qquad\qquad\text{(Ohm's law for materials where V}\propto \text{I)}$$ $$\text{...
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1 vote
2 answers
185 views

Finding current through a specific resistor

I am relatively new to circuits. I am struggling to find the current through the resistor here, R1. All I understand is Ohm's law and parallel and series resistors, but I don't know how to apply it ...
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3 answers
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Finding Current Used by an LED

In the Arduino Start Kit, the first circuit is very basic: 5V power, 220 ohm resistor, and an LED with a forward voltage of 2.2V. However, here's two things I can't reconcile: The booklet says that ...
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-2 votes
1 answer
70 views

Calculate total resistance. (Circuit analysis)

How do I solve this circuit and determine the total resistance between A and B if all the resistors are 120 Ω? Thank you.
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1 vote
2 answers
113 views

Using current division to find voltage

I'm a beginner in electrical engineering. I am having trouble with this circuit analysis problem. It asks to simplify the circuit into an expression for \$V_L\$ in terms of \$R, R_L,\$ and \$i_S\$. ...
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Why does the voltage decreases when current increases?

I have a 24V battery powering a brushless DC motor. When the motor runs at low RPM and draws, say 10A, the battery reads 24V. If I go full throttle for a second, motor will draw 60A and battery will ...
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2 answers
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Current calculation - basic circuit

I’m just starting off, and I’m watching a series of videos about the basics of electric circuits. https://youtu.be/lf0lMDZVwTI As you can see in the the picture, the teacher solved the current of the ...
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1 answer
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Calculate series resistor value for LED on 220 Vac RMS supply

The traditional way to find the resistor value I can find on the internet is: (Input Voltage - Forward Voltage) / Current In my case, the Input Voltage is 200 Vac, ...
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3 answers
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Help a beginner understand if a design is correct

I'm fairly familiar with Ohm's law and I did some calculations I'd like experienced engineers to confirm if it is correct or point where I made a mistake Here's the idea I want to power a self-made ...
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0 answers
53 views

Calculating line currents in three phase grid

My original network looks like this: I'm trying to find the line current $$l_{l, 1}$$ the red one at very top. Here is what I have done: I converted the delta impedance circuit in the right to star, ...
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5 answers
151 views

Ohm's law Vs. Ohm's relation (which one is right)?

Ok, so this might be a stupid question but I just had to ask. We are all taught that Ohm's law is: V = IR I have heard some people that insist that it should be called Ohm's relation instead of ...
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2 votes
4 answers
620 views

If voltage and current are inverse to each other, how do we get higher power?

I am dazzled; I'm young (teen) so am not too good, but I am wondering if current is proportional to voltage, how do we get high power? What I'm trying to say is that if we were to have a 5 V supply, ...
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3 answers
148 views

If a voltage source is current limited does this actually mean that the voltage across the load is limited?

For the past while I've been struggling to wrap my head around electricity. One thing that has puzzled me to no end is the relationship between current and voltage. On paper it's a really simple ...
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24 votes
5 answers
4k views

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 ...
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10 votes
14 answers
5k views

Should I take Ohm's law for granted?

I have started recently on the study of electronics. One of the most basic statements that I learned about electricity is the relationship between the voltage and the current across a conductor. I did ...
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