# 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.

314 questions
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### Maximum Sound out of a Speaker

I am new to electronics, so please excuse the noob question. I have an 8 ohm 1/4W speaker. I would like to get the loudest sound out of it that I can. Based on my understanding, which may be ...
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### Improve input audio signals to car audio system

I am helping a friend to solve a low and not so clear sound to his car's audiosystem, when using aux-input in particular. He is getting great signals from CD or Radio, but when he feeds the ...
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### Calculating Necessary Resistance In Current Source Circuit

I have a problem where I must calculate the resistance required in R3 to have 1A flowing through the two 9.7V sources in the image below (i.e. Charging the batteries at a rate of 1A). I have ...
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### How can I calculate current(I) when I don't know voltage drop

So everyone knows Ohms law ($I=\frac{V}{R}$) . Let's say I have a 9V battery and a LED. Furthermore the LED only needs 1.9v so the voltage drop of my resistor would be: $9-1.9 = 7.1\mathrm{V}$ ...
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### Ohm's law to calculate voltage [closed]

I know this is a bad idea in practice, I'm more concerned with the theory. How would you use ohm's law to solve this problem. Given V = IR I have a 12v 10amp DC power supply. I want the output ...
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### Simple KVL Problem Not So Simple

We're only a week in to the first EE class here at Uni and I'm already stumped. I can build a power supply in my sleep but anything theory-related turns me upside down. Now, I've done KVL on the ...
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### Thevenin's equivalent exercise

I have this exercise of a Thevenin's equivalent that really got me confused with it's usage of a transistor and was wondering if I could get some help with understanding how to solve this particular ...
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### Simple circuit with transistor using Raspberry Pi

I'm trying to use a Raspberry Pi to control a set of 4 LEDs. I'd like to control the LEDs in software by using a ...
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### Calculate total impedance in RLC circuit with L and C parallel

I am trying to find the total impedance of this circuit but im not getting the right answer. According to my notes the total impedance is 1002 Ω, -86.6°. This is the method i tried: I got Xc = 111....
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### Lithium-ion battery Internal resistance myth

I am making a battery tester, lithium ion battery for particular. and I want to measure the internal resistance, but after testing few cells, I am skeptical for my results, since most of them, new or ...
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### Resistor and voltage of a circuit

I'm a beginner in electronics and I was studying when I had a question, how to calculate the voltage after passing by a resistor. Ex: there is a circuit of 10mA with a 5V voltage, what is the voltage ...
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When you have one resistor in a series circuit, the amount of voltage taken up by that resistor is 100%. Adding another resistor (same Ohms) makes that voltage drop 50%. Why, since only current should ...
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### How to find the power dissapation of a resistor

I am attempting to repair a circuit (DC-AC inverter) and have incountered a resistor with discolouration. The measurements indicte a resistance of 1.5Mohms or usually OL leading me to belive the ...
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### What damage can 1500V cause to a circuit? [closed]

I'm working on a device that has a supply of 220 V. The output has an LED at the end of a fibre-optic cable coming from the device in question. If, for some reason, a tremendous amount of voltage ...
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### Voltage Divider producing unexpected voltage

I am attempting to create a voltage divider that create 4.5 volts from a 9v battery. Using the voltage divider equation 4.7k / (4.7k + 4.7k) ) * 9v = 4.5v, I ...
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### How to find the current in a complex circuit with nodal voltage sources?

This is circuit. Not sure how to get V, and find current. Any help?
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### Measurement of power dissipation in a resistance

In the above figure (step up transformer), We can calculate $V_s$ using $\frac{V_s}{V_p}=\frac{N_s}{N_p}$ and $V_s=50 V$ So, power dissipated in the resistance, $P=\frac{V_s^2}{R}=2500 W$ (...
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### What is the difference between Ohmic and Non-ohmic devices? [closed]

Besides the fact that one does not following Ohm's law, are there any other differences between these conductors?
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### How do I solve this electrical circuit?

The voltage across R is Vr. I want to plot I vs Vr on a graph. Given I = 6k mA. Now, my question is this: wont I vary with varying V1? Did I copy something wrong, or is there a way to plot this?
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### Switch mode PSU minimum load

Alright, I know I am going to get a lot of flak for this, but let me reassure you that I have already spent the last few days reading on Google while going back and forth from the bench to test ...
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### How to calculate the base-current of this transistor?

Newbie in eelctronics here. How would you calculate the current trought the base of the first transistor? simulate this circuit – Schematic created using CircuitLab follow-up question: What is ...
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### how to determine resistor value calculation for common anode 7-segment display multiplexed

Resistor is required to limit the current flow through the LED since otherwise so much current will pass through that power dissipation shall destroy the LED in less than a second. For nonmultiplexed ...
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### Power calculation and Ohm's Law for Reactance

Hi I have the following question: V = 120V, I = 10 A, I lags V by 60degrees simulate this circuit – Schematic created using CircuitLab The load consists of a resistor and an inductor in ...
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### Ohms to volts i [closed]

Hi I am not sure if I understand this! Ok if I have a power source of 5 volts which then has a resistor of 6ohms and another resistor of 4ohms in parallel with a volt meter would I add the two ...
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### Understanding Ohm's law(?) for transmission lines

I have this easy schematic Next to this is stated that: $$Vb = \frac{Z_{in1}e_{b}}{R_{B}+Z_{in1}}$$ non Latex-version of the formula: Vb = (eb*Zin1)/(Rb+Zin1) I would like to know from where this ...
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### Why Ohm's Law and Kirchhoff Laws give different results?

I would like to know why Ohm's law and Kirchhoff laws give different results for voltage as said in this lecture(p.19) by Dr. Sheryl Howard. Even though the change is small in voltage it gave me very ...
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### Arduino powering an external circuit with higher voltage

First of all, I'm sorry for the newbie question. I'm a software engineer and only a hobbyist in electronics. I'm trying to power up an external circuit using an Arduino digital pin. The external ...
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### Calculating voltage spike of an inductor

Suppose there is a circuit like this where the inductor has no resistance In this circuit, if Switch 1 is initially closed, then there is 10/100 = 0.1 A of current flowing through the inductor. ...
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### What does will happen in real and written?

Explain please i'm confused :/ What would happen if a wire having no resistance were connected directly across the terminals of an 8V battery? How much current would result, according to ohm's law?
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### Why isn't Ohm's law working for this simple circuit?

I have a 70W 12V-500V DC power converter, and something in these pictures is not adding up. I run the 500V output through a high-voltage 332kΩ resistor. Now, using the left multimeter I ...
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### Calculate current with potentiometer

I've built a circuit on a breadboard using a 10K potentiometer, a 220 ohm resistor and a LED. They are connected in series. Using Ohm's law, you find that: Total resistance \\$R = 10000 + 220 = 10220\...
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### When do I need a resistor during LED flashing? [duplicate]

My goal is to flash a few white LED in serial using 9V battery. Here are the specifications of this LED. As I saw the Forward Voltage is 3.4V, but what does it really mean? Can't I plug this LED ...
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### Replacing electric Ice Machine Motor with a resistor in a Samsung Refrigerator

We bought a house 3 years ago and it came with a Samsung Refrigerator. For some reason the previous owner bought a fridge with an ice maker and never hooked it up. Well you cannot disable this feature ...
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### How (or if?) to isolate inputs to op amp summer?

I am building a function generator as an exercise. I have a 9V power supply that I split into +/-4.5V. The +4.5V side powers an Arduino that outputs the waveform as a series of 8-bit values on ...
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### Basic Circuit Analysis using Kirchhoff and Ohm's Laws

So I'm in an introductory circuit analysis class where all we have learned so far are Kirchhoff's and Ohm's Law. I am practicing how to solve these circuits, but for some reason I can't understand ...
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### Does changing the Voltage and the Current passing through an LED affect the result in the same way?

More directly : passing electricity that is 0.5 times the amperage of the one required will make the LED half bright, right? Is it the same with halving its voltage requirement? Or will it not turn on ...
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### Why can people touch high voltage?

So I know that you need a certain current flowing through you to die, I've heard from some people "its the amps that kills you", and from others "Its the volts that drive the amps" and I realize ...
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### Calculated resistance of an LED [duplicate]

I am working on some circuit lab homework this week and am a bit stumped by something I just can't seem to find anywhere in my Circuit Analysis I book. The lab has me construct the following circuit ...
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### Power consumed by an LED in a simple circuit

I am in the very beginnings of studying circuits and am a little confused on calculated Power. If I have a 9V Battery, 4 x 10k Resistors and a single LED, how would I calculate the power consumed by ...
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### If I put 12 volts across a 1 ohm resistor, will it pull 144 watts?

I would think putting 12 volts across a 1 ohm resistor would pull 12 amps of current, and since watts=volts*amps the resistor would be dissipating 144 watts of heat, all of this assuming the source ...
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### When does a resistor affect current and voltage?

I was playing around with a computer power supply and some resistors and noticed that raising the ohmage decreased the amperage but the voltage was unaffected. Does this mean that voltage is a ...
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### Resistors for transistor led circuit

Im new to electronics and have problems with calculating the resistors needed for driving an IR LED with an transistor. My VDD is 3.3V, the LED needs 1.3V and I want to drive it close to 20mA, so I ...
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### Why does a resistor reduce voltage if V=IR? [duplicate]

I'm sure this is a very simple question, but I have been confused about this topic for a while now. According to Ohm's law, resistance varies directly with voltage. This means that if resistance ...
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### If V=IR Why are voltage and current interchangeable through a constant resistance [duplicate]

I hear people say things like "I only put 5 amps through the circuit but I put a bunch of volts". I don't understand how this is possible if V=IR. Lets say you have a circuit with 5 ohms of ...
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### Can I use V=IR in the analysis of AC circuits?

My textbooks usually just assert this relation so I don't really know when it doesn't apply. EDIT: Reflecting on this question, I wanted to clarify that I wanted to know if Ohm's Law is valid for ...
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### A-Level Physics: What is the current needed to maintain the wire at a steady temperature of 387∘C?

I am stuck on answering an A Level physics question: When a current of 5.00A flows through a tungsten wire in a stream of air at 27.0∘C, the wire attains a steady temperature of 57.0∘C. It may be ...
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My first question on EE, please be kind. :-) I am trying to learn how the ADC works on this Cypress PSoC 4100 board. The circuit in the picture does nothing but power the board, connect it to the ...
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### why my power calculation for this resistor is wrong?

i encountered a very simple question in a test and i easily calculated the answer but somehow i am making a mistake because i can not find my answer between the available answers, what am i doing ...