# 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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### Volts for power supply, and ohms and watts for the resistor [duplicate]

I'm very new on this for this has never been taught in my school. I have ten 5mm blue LEDs. Each led has 3.4V and 30mA max current. The only thing I know is that I have 34V for my LEDs. The power ...
1answer
908 views

### How does an MCU pin detect a voltage?

If I have an MCU pin connected in between 2 resistors (a voltage divider) how does the MCU ...
2answers
96 views

### Calculating for current in a single transistor amplifier(almost common collector?)

I was given this circuit for a practice test during one of my classes, but we were never shown how to actually solve it. It's just been bugging me so I wanted to know how others solved for all the ...
3answers
256 views

### Why is the calculated current with P=VI and R=V/I not equal?

I'm just starting to learn electronics. I thought I'd start with a simple project of attaching a speaker to a Raspberry Pi (it supplies 3.3V). The speaker I've picked is an 8Ω 0.5W speaker. Now as I ...
3answers
415 views

### Sparkfun using 500Ω resistor on circuit with 9V battery and 2V/0.018A LED

A Sparkfun tutorial explaining voltage, current and resistance shows a simple circuit where a LED is powered by a DC source (9V battery). The LED is a red 2V/0.018A LED. The tutorial explains that ...
2answers
225 views

### Can anyone explain the ohm's law apply here?

What i am seeking is to explain why the relationship here is not V2/R2 instead it's given as (V1-V2)/R2
1answer
10k views

### How is open-circuit voltage calculated?

I'm pretty new to circuits and I only know basic rule from Ohm's law that U=I*R. I quite don't understand how was following formula for Ui created: Why are there only two resistances in numerator? ...
2answers
244 views

### 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 ...
1answer
295 views

### 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 ...
4answers
316 views

### 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 ...
5answers
1k views

### 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: $9-1.9 = 7.1\mathrm{V}$ ...
5answers
255 views

### 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 ...
2answers
443 views

### 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 ...
1answer
310 views

### 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 ...
3answers
5k views

### 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 ...
1answer
898 views

### 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....
3answers
6k views

### 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 ...
2answers
181 views

### 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 ...
5answers
1k views

### Why does voltage split when an additional resistor is added?

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 ...
1answer
76 views

### 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 ...
2answers
60 views

### 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 ...
2answers
233 views

### 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 ...
1answer
137 views

### 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?
2answers
1k views

### 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, $P=\frac{V_s^2}{R}=2500 W$ (...
2answers
4k views

### 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?
2answers
70 views

### 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?
3answers
2k views

### 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 ...
2answers
311 views

### 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 ...
1answer
3k views

### 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 ...
2answers
136 views

### 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 ...
2answers
365 views

### 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 ...
1answer
140 views

### 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 ...
1answer
494 views

### 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 ...
4answers
706 views

### 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 ...
2answers
3k views

### 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. ...
2answers
75 views

### 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?
3answers
461 views

### 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 ...
1answer
382 views

### 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\...
1answer
185 views

### 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 ...
2answers
274 views

### 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 ...
1answer
267 views

### 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 ...
2answers
282 views

### 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 ...
2answers
2k views

### 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 ...
1answer
866 views

### 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 ...
2answers
536 views

### 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 ...
1answer
118 views

### 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 ...
2answers
806 views

### 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 ...
1answer
807 views

### 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 ...
2answers
1k views

### 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 ...
5answers
13k views

### 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 ...