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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48 views

What value resistor do I need? [closed]

I am new to electrical engineering and find ohms law confusing. I have measured the values of 2 circuits as follows. 6.70V 0.1mA 5.64V 0.06mA What I want to do is match the voltages.. but I find ...
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Voltage drop on resistor with MOSFET configuration circuit

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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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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1answer
47 views

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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735 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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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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1answer
60 views

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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61 views

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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729 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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101 views

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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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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626 views

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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138 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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107 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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2answers
50 views

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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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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188 views

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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92 views

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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1answer
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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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118 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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66 views

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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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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2answers
81 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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75 views

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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79 views

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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191 views

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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148 views

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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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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5answers
144 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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4answers
550 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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109 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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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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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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2answers
76 views

LED driver does not give constant current with a load

I'm working with an AL5810Q, which is a linear LED driver where the current can be set with only one external resistor following $$I_{LED}=\frac{750}{R_{SET}}.$$ With that, since I need a current of ...
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90 views

Limitations Of Ohms Law [closed]

Sometimes i think why the heck this ohms law created to make troubles for us, as nowadays i am deeply working on Basic Electronics so there Ohms law actually sucks... I was studying transistor ...
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1answer
74 views

Effective resistance from a random resistance network

I am trying to calculate the equivalent resistance from a random resistance network formed by carbon nanotubes (CNTs.) I have a MATLAB program where the CNTs are randomly distributed inside a volume. ...
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2answers
286 views

How to test a Peltier module TEC1-12705 to determine if it works as intended?

Background: The module comes from a 70W mini-cooler which doesn't really cool anymore. I took it apart and got the module out, I could read the model TEC1-12705 from the module itself. The ...
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Weird MOT current measuerements

I have MOT transformer, which I want to use for DIY spot welder. I measured 0.85V on one turn of primary open circuit, it means cca 2.55V on three turns etc. This seems ok. What I do not however ...
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49 views

AC parallel and series circuit

I have this AC circuit: simulate this circuit – Schematic created using CircuitLab I have found VA which is \$222 \angle-119 mV\$. The current flowing through the inductor \$IL = 2.6 \angle-89 ...
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1answer
169 views

How to determine what voltage and current I should use for a Kanthal heating element?

I'm in the process of making a plastic forming "tool". It has a hot wire inlaid into the top. I have not come up with the power supply yet but have a few iron core transformers laying around....
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1answer
190 views

Using KCL, KVL and Ohm’s Law find I0 in the circuit in Fig.1.1

I have spent more than 8 hours studying KCL and KVL and Ohm's law but I still can't solve this : If anyone can help me understand how to find I0, Ix and 2Ix I will really appreciate it.
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101 views

How to choose a perfect resistor to LEDs to get same brightness?

I'm using 5 different LED to indicate water level. I used a 330ohm resistor to all LEDs. Some LEDs glow brighter some are less bright. How can I calculate an exact resistor value to my LEDs to get ...
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1answer
97 views

INA219 Voltage measurements meaning

I have a battery holder, 3 x 1.5V AA, connected to a resistor (100 Ohm or close), LED and Adafruit INA219 breakout board. The bus voltage reading from the INA219 reports 1.0V. Where does this number ...
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84 views

Limit current to a load

I'm making a little heated greenhouse. I have three 1.2 ohm 5W resistors and a 5V 1A power supply. Everything is controlled by my Arduino through a MOSFET. Now, I would just need 5W of power to keep ...
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61 views

Current to voltage circuit

I'm currently doing a project that consists of testing bio-implants to see if they are still good to use. For this, I have to measure the impedance of the implant from frequency starting at 10Hz to ...
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86 views

How to calculate the resistor value necessary for the columns 8x8 led matrix?

I am building an 8x8 led matrix using 5mm LEDs (3.2V, 20mA). I connect it to the arduino UNO through the I2C using the GPIO expander MCP23017. The circuit is as follows: A matrix column is made up of ...
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1answer
39 views

Analyzing a circuit with 2 voltage sources

This is a problem given to us for homework: This is the first question I've got that has 2 power sources and I'm stuck on calculating the potential difference and current through R3, R4, and R5. I ...
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1answer
56 views

House refurb rewire - low current?

So we've been renovating (virtually new everything) a 1930s semi that hasn't been modernised since it was built and hadnt been lived in since the 70s. Naturally a full rewire was high on the agenda ...
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2answers
171 views

Ohm's law paradox?

I have a chain of 4 single resistors in series. Call them R1, R2, R3, R4. When I measure the total resistance from top to bottom, then I get the same result as if I measure each pair of resistors: (R1+...

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