# 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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### 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 ...
1 vote
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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 ...
1 vote
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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 ...
329 views

### 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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### If batteries are arranged in series in a closed circuit (I.e. with a load, which is constant) why doesn’t the current increase when voltage does?

I guess people have asked slightly similar questions to mine before, but I still haven’t been able to find a complete answer as to WHY the current doesn’t increase even when the voltage in a circuit ...
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### Applying Ohm's law to household AC

I am a hobbyist trying to select an appropriate relay to control the heating profile of a DIY coffee roaster. For years, I have been varying the heating duty cycle by manually turning the heat OFF/ON. ...
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### Heating resistor - low current, high temperature

I am looking for a heating resistor (strip), but I would like to keep the current as low as possible. I know that heat is (created and) directly proportional to current and not voltage but on the ...
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### Is this a good way to think about solar cells?

Imagine we want to power a load with resistance R with a Solar Panel. To figure out how the solar panel will interact with it, draw a line with slope 1/R on an IV graph. Where that line and the solar ...
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### Why does voltage end up dropping in a voltage divider circuit?

Consider the following situation - A simple series circuit with a 10 V power source and two 5 Ω resistors I know that a voltage drop of 5 V would occur at each resistor due to Ohm's law and the ...
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### Is Ohm's law really accurate?

Say I had a component with a resistance of 100 Ω, and I attached a 12 V power supply across its terminals using: a thin wire a thick wire Would the component in both cases really draw (12 V/100 Ω) A?...
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### What does voltage drop mean in a circuit? [duplicate]

Let's calculate the voltage drop per resistor: total R = 1000 + 680 = 1680 Ω. circuit I = 5/1680 = 2.97 mA. v1 = 0.00297 × 1000 = 2.97 V = voltage drop across R1 v2 = 0.00297 × 680 = 2.01 V = voltage ...
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Power adaptors usually have a fixed voltage (i.e 6 volts) and a maximum available current (i.e 1 ampere.) A device can draw as much current as it needs up to the maximum amount the adaptor provides. I ...
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### Using Ohm's law in a simple circuit with a DC power adapter

I'm a bit confused on using Ohm's law so I'm going to ask about it using an example. I have a simple circuit with power provided by a generic DC power adapter and a 1 kΩ resistor. Say the adapter ...
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### What are right or best analysis method on finding voltage, current and ohm in circuit analysis?

I'm new to electrical engineering. In the few past weeks, I already learn about different analyses to find what to find. Like finding voltage, current, and ohm with different methods. Examples like ...
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### Why is the current the same across these resistors?

I am learning about op-amps from this tutorial from Circuitbread.com on YouTube. The instructor states around the 9:30 mark (video clip): Because we have 1 mA (through i1) we know we have 1 mA (...
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### Component requires specific voltage and current but the math doesn't add up

I'm trying to get an old soviet era cathode ray tube working. On the data sheet it says the heating element needs between 5.7V and 6.9V, and between 0.54A and 0.66A, but I've measured the resistance ...
1 vote
199 views

### How do transformers comply with Ohm's law and KVL?

I understand how to use a transformer in practice, and I know that transformers obey the law of conservation of energy, but I'm confused as to how step-up and step-down transformers obey Ohm's law and ...
120 views

### A battery with zero internal resistance connected to identical resistors in parallel

How is it possible that the current in each branch of a set of identical resistors in parallel would change when adding one more parallel resistor? I know that since the battery doesn't have internal ...
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### Current, voltage, and power interpretation

I have been working with circuits a lot more lately and not just modeling them. I think I never had a good enough understanding of the fundamental theory of voltage, power, and current. Voltage is ...
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### Help understanding power requirements from computer datasheet

I wanted some advice on how to read power specs from a datasheet. There's a computer I'm trying to power. The datasheet simply says it needs 12-19V input voltage. However, it says the buyer is ...
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### Equivalent resistance in simple Current Circuit

I have the following circuit (below). In order to calculate the current I1 as a function of the resistors and the voltage of the circuit, I'm doing the following: ...
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### Doesn't the law of conservation of energy invalidate Ohm's law?

Imagine I have a power supply supplying a 12 amp AC current of 12 volts. The resistance of the circuit, consisting of only a copper wire and a resistor, is 1 ohm. In this instance Ohm's law holds true:...