# 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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88 views

### IR Blaster Resistor Calculation for IR LED (breaking ohm's law?)

We are trying to build IR Blaster based on schematics provided by Tuya. I believe Tuya based IR blasters sells hundred of thousands per month if not millions. So I am quite sure that their schematics ...
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### Why, when conductors are connected in series, their current strength is equal?

Why, when conductors are connected in series, their current strength is equal, because the resistivity of the conductors can be different?
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### Do components "draw" current, or is it forced through them? [duplicate]

If you attach a typical LED to a 9V battery, the LED will burn out because there's too much current. If you add a resistor, it's fine. You can charge your phone with a 1.0A charger, a 2.4A charger, ...
1 vote
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### Adding Resistor to Match Power Draw for Fan Replacement

I'm replacing a 12V 0.23A fan with a 12V 0.06A fan and want to keep the power draw the same. I believe there is load-sensing at the power supply side, which detects lower draw and shuts down due ...
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### Would a current pass in a resistless wire, like a superconducting one, when its ends are connected to the terminals of an ideal battery?

Would a current pass in a superconducting wire, when its ends are connected to the terminals of an ideal battery? If the answer is yes, wouldn't that violate KVL because the voltage rise in the source ...
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### Load draws more current that power supply provides

I have a power supply that pushes a maximum of 30V and 5 amps. If I push 30V through a load that has a resistance of 3 ohms, the load would then be drawing 10A, right? 30/3 = 10. (Ohms Law). This is ...
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### Adjusting underfloor heating thermistor resistance to match a different controller

I have DeviMat underfloor heating installed in my bathroom, presently matched to a Danfoss DeviReg "smart" thermostat. There's a matching Devi heating probe installed under the floor which I ...
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### calculating total current consumption before and after voltage regulator

I have a simple circuit. IC1 is a standard 7805 voltage regulator. Let's assume the battery G1 is 10 volts and all LED's each have 1V for its voltage drop. Do I calculate total current consumption as ...
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### Determining if a multimeter will damage ICs - How to confirm?

I’m looking for a straightforward way to determine if a particular multimeter will damage sensitive electronics such as ICs. Specifically, let’s say I have a Fluke 117 multimeter and I am trying to ...
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### How to formulate an equation for the electrical circuit with both a voltage and a current source?

This problem asks me to find Rx, the electrical power of each element and the algebraic sum of the electrical powers of all elements. How to apply Kirchhoff's and Ohm's law correctly in this problem? ...
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### How to determine equivalent resistance between terminals?

What kind of symmetry I can use to get the result? I think I have to redraw a circuit, but how?
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### How to calculate the value of resistor R2?

How to find the value of R2 in this circuit? If I1 is 8 mA in this case (I = I1 + I2) and then given 5 V over R2 and R3, 5 V/0.008 A = 625 Ω. Is this answer valid ? Or is it 5 V/I = 2mA = 2.5 = 1/2.5 +...
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1 vote
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### Calculating Currents and Power in a Circuit with Multiple Resistors and a Voltage Source

I'm currently working on a project that involves a circuit with a single voltage source and multiple resistors, and I've hit a snag with my calculations. I could use some guidance from anyone who's ...
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### Why is Joule heating (or electric power) proportional to current squared? [closed]

I know, that the formula P = R·I2 is derived from the formula of electric power and Ohm's Law, but the intuition behind why the current is exactly squared here is unclear to me. I get that the more ...
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### How to calculate total resistance and identify which resistors are in series?

How to calculate the total resistance and identify which resistors are in series? I'm really lost with this one. How do I properly read this?
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### Confused about usage of Ohm's law & Kirchhoff's laws to solve a circuit

I'm solving this circuit using Ohm's law and Kirchhoff's laws: I solved the circuit correctly the second time. Equation A: $$I_1-I_0-6=0$$ Equation B: $$-120\ \mathrm{V}+I_0\cdot 10+I_1\cdot 50 = 0$$ ...
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### Parallel circuit calculations [closed]

This is definitely a very simple question for those in this community but I’m in a bit of a jam here. I did a lab where we simply measured the current, voltage and resistance on a low voltage trainer. ...
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### Reasons to use combinations of resistors (parallel or in series): Looking for educational examples

I teach physics at high school level, and one of the topics I cover involves instructing students on how to calculate the total resistance of two resistors, whether in parallel, in series or simple ...
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### Diode in reverse lights up LED

I have small issue with my circuit that I can't wrap my head around. I have made a custom PCB powered both by USB and battery. I put a diode between them to block battery power from flowing into USB ...
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### What resistors for a 4 LED Arduino/breadboard project?

I am currently working on a school project for my work-study. The project is super simple: light up 4 LEDs, in various patterns, using a push button to cycle through the modes. I'm using 4 colored ...
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### Different answers from mesh analysis and voltage division

This is a problem solving for the voltage across a capacitor with initial conditions. After finding initial conditions and transforming into s-domain, the circuit looks like this: So, the voltage we ...
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### Observed voltage unexpected in simple test circuit with one resistor

I have a 1.65v regulated source (max 50mA). I'm observing 1.71v with no load. I've added a 178 ohm resistor (verified with VOM). I'm observing 1.60v 9mA across the resistor pins. V = IR; V = .009A x ...
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### How to determine the collector current limiting resistors for the Darlington's pair of transistors?

How were the resistors in the circuit calculated?, I would like to come up with a similar circuit but for a 5VDC power supply, and I would like to resize the resistors as per my load requirement, my ...
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### A question about the validity of impedance rules

Let’s consider an RLC circuit connected with a sinusoidal source, my goal is to find the current $I(t)$, this is done by solving the following differential equation: \\$ \frac{{d^2I}}{{dt^2}} + \frac{...
1 vote
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### How can I measure the resistance of non-linear devices using a digital multimeter?

Is the value of resistance that appears when we measure the resistance using a DMM at the terminals of any electronic device the total equivalent resistance of that device which is also called load ...
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### How to predict the voltage drop due to a fuse?

My device runs from a USB supply, typical 5V, current typically 20mA, never beyond 100mA. I want to add a fuse. The JFC0402-0500FS claims rated current 0.50A (perfect for this application) and a ...
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### How can I maximize the power consumed in this resistor?

simulate this circuit – Schematic created using CircuitLab I have gotten really stuck on this question. The question is: Determine R3 so that maximum power is consumed in R3. What is that ...
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### Relation of Power, Voltage and Current in Buck-Boost DC-DC Converter

I've been searching information of this topic for many days but I've not get an answer that convince me yet. I designed a DC-DC buck-boost converter a couple of years ago with 0.8-20 V and 2.7 A as ...
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### Why is my expression for current I(2) wrong?

simulate this circuit – Schematic created using CircuitLab Hi! My question is if I(2) is a current that runs from Node 1 to Node 2 then the expression of I(2) as a function of I(A), I(B), R1, R2 ...
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### What is I1, I2, I3 and I4?

simulate this circuit – Schematic created using CircuitLab I have really gotten stuck on this question where I need to calculate I1, I2, I3 and I4. The numbers for the circuit is: V(a)=2 V, V(b)=...
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### Body impedance and electrical stimulation. What is the skin load in electrical stimulation?

An electrical stimulator device like Geko T-1 provides a 27 mA output current. On the specification for the load impedance range they mention a 200 Ω to 3 kΩ range for 27 mA output. How did they ...
1 vote
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### Voltage difference between two nodes surrounding a source [closed]

In the schematic you can see I have this circuit that includes a branch leading from ground to a 10Ω resistance, a 4V DC source and up to node A. I am trying to solve this circuit using the node ...
1 vote
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### Why is clockwise KVL done like this?

My task is to find voltage across the resistor of this circuit where all the 4 components are connected in series with each other. The given information are : V1 (t) = 100 * sin(100 * t) V, R = 100 ...
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### How is current dropped through a step-up transformer, when current is dependent on resistance?

Suppose you have a 1:10 transformer. You put in 12V and you get 120V out the other end. Now the current before the transformer would be $$V=IR$$ $$I = \frac{V}{R}$$ $$I = \frac{12}{1}$$ $$I=12$$ (...
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### Can Watt’s law be derived from the Ohm’s law without using calculus?

Unlike Ohm’s law Watt’s law is not a fundamental law of electronics, as it can be derived from other fundamental laws of electronics. In the derivation above (see the pic) I used definition of current ...
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### How to calculate unknown resistance from known current in the vector-matrix form of Ohm's law

I was trying to answer this question (pic 1) using the following method (pic 2): Step 1. Apply junction law to find the current vector. Step 2. Apply loop law to find the voltage vector and resistance ...
1 vote
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### How to choose a diode and adapt a charging circuit so it can sense temperature from two battery stacks instead of one?

I have two questions regarding the schematic below. Diode D3 (D2 in the datasheet) at location A3-A4 is not defined in the datasheet. R9 (R2 in the example) is sized at: 220Ω. The input voltage is 9V. ...
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### Finding resistance between two conductors

For my electromagnetic-field class we are asked to calculate resistance between two electrodes shown as below. The part c(i) is just a simple resistance question using the formula R=pl/a. I don't ...
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### Calculating resistance of a load

I have a schematic with LEDs. Let's say every LED takes 1.85 V and 20 mA. I want to find a resistor with the same resistance as the LEDs. How do I use Ohm's law? 1.85 / 0.02 * 6 or (1.85 * 2)/(0.02 * ...
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### Urgent question regarding resistance of water

I have mentioned before that I am currently in the middle of a university project where I am discussing electrical safety of water. I want to work out what the current would be at mains electricity ...
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The reason why nichrome wire heat up is usually explained by the fact that it has high resistance. While I don’t doubt this explanation, I can’t get my head around the following “paradox.” If the ...
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### Voltage drop, how much?

I'm making a 12 V test box for trailers. I just wanted to know if I add a load (let's say a 12 V LED light), will this provide enough of a load to show a voltage drop? I'm trying to pinpoint any ...
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### Does Ohm's law always apply at any instantaneous point in time?

I often see people saying "Ohm's law doesn't apply here", usually in relation to AC circuits and diodes. They describe certain situations as being "non-Ohmic". My understanding of ...
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### How to find total resistance of this circuit?

I have a terrible prof who didn't teach anything about this. I understand how to find parallel and series resistances, but am thrown off by the 4 Ω resistor in the middle.
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### Heater (resistor) combination to achieve specific power

I am designing a heating circuit composed of ceramic heating resistors. I have a 24 V supply and I am limited to 3 A, which allows me to disipate total of 70W, which is my target. I have a limited ...
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### Using resistor to drop voltage in circuit with changing current [duplicate]

I have no problem calculating and understanding how to drop voltage using resistor for circuits with purely resistive loads - for example look at much current will an LED draw, subtract source and LED ...
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### Is it possible to have a resistor network whose total value is unsolvable?

Home hobbyist here. I've been doing a lot of theoretical resistor, voltage divider, Ohm's law, and Kirchhoff law type problems just for practice, and ran across this older video on YouTube, which ...
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