# 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 (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 ...
297 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 ...
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 ...
931 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 ...
668 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 ...
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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 ...
932 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 ...
838 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 ...
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 ...
16k 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 ...
331 views

### 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 ...
7k views

### 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 ...
259 views

### 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 ...
2k views

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 ...
779 views

### How does a 'voltage drop' work?

It is my understanding that, in an electric circuit, voltage is divided amongst components in a ratio determined by their various resistances. That is, for example, if a 5Ω‎ and a10Ω‎ resistor were ...
293 views

### How do voltage changers work? Can you change any voltage to any voltage?

I often hear about changing voltage. Like someone would say "I bumped 12V to 38V" or like "I converted these 100V to 10V". Can you change any voltage to any voltage? What's the exact mechanism for ...
392 views

### Verification on Ohm's Law?

I'm building some Heated Motorcycle Grips and I think my calculations are off. Can anyone help me verify that for 10 feet of 20 gauge Nichrome 60 wire, I have the correct Ohms, Watts, and Amps for the ...
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### Basic circuit analysis question [duplicate]

Why current is negative in this situation? Because EMF and current directions are the opposites? simulate this circuit – Schematic created using CircuitLab Can someone give me a good ...
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### arduino current

I want to start learning EE with Arduino so as a project I decided to build an Ohmmeter and measure a (specific) resistance that should be about 100 KΩ ±50KΩ. In order to probe for that resistance I ...
834 views

### Amp Limitation on 120v Circuit

If an engineer needs to limit how many amps come out of a wall's circuit, how is this accomplished? I know that there is nothing preventing more than 15 amps from coming through my wall other than the ...
182 views

### resistors misconception - is current-limiting effect circuit-wide?

Resistors are used to drop current Amp and Voltage, following Ohm's law. I can't understand some of their applications: we use them cause we sometimes want to drop the voltage a little in a specific ...
270 views

### What is the efficiency of electric power converted to heat?

I'm trying to understand how much heat is generated when a given amount of electric power is drawn. And from what I understand, it's pretty much 1 to 1 isn't it? Example: If I have a 1 HP motor ...
370 views

### Molybdenum Heater Wire

I have a 12 foot length of 14-gauge molybdenum wire that I have measured a resistance of 1.2 ohms. I would like to use it as a small heater coil. How can I calculate the safe number of volts that I ...
2k views

### Determining Resistor for Heating Element

I am attempting to run a Molybdenum heat coil. The best I can tell it is 0.3-0.4 ohms per rack and I would like to run say two racks at 230V at 3.9KW (so it doesn't trip my 230V 20 amp breaker). Does ...
42k views

### Power's relationship to Resistance

$$\frac{V^2}{R} = P = I^2 \cdot R$$ According to this equation, Power is inversely proportional to resistance on the left side and directly proportional to resistance on the right side. How can ...
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### Why can Ohm's law be used in a linear circuit with multiple equivalent resistors without being given current?

I'm exploring voltage dividers and am puzzled by the conclusion made by the YouTuber in this video: "If you apply Ohm's law, you find that 1 V spread across two equal-value resistors gives you 0.5 V ...
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### Calculating sum resistance of multiple series and parallel resistors

! I know how to find resistance, current, and voltage through series/parallel circuits. The problem I'm having is figuring which part of this circuit to simplify first. What is the correct order of ...
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### Why are these readings violating ohm's law? (Are they?)

I'm brushing up on my high school electronics knowledge and I decided to experiment with a small acquarium pump I had lying around. I took some measurements with a multimeter and the results confuse ...
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### Equation for splitting a charge between n wires

If I had a 10 amps of current that was split down two wires, one with 1 ohms of resistance and another with 2 ohms of resistance, what equation would I use to determine how much charge went down each ...
492 views

### Simulation measured voltage not matching calculations

Ok, so I have the following circuit: click here for simulation The source voltage is 5V. The voltage measured between A and B is 2.44V, which differs from what I get by calculating that same ...
580 views

### If adding resistors in parallel decreases total resistance, why doesn't the voltage in the circuit change?

I'm sure I'm missing something basic, but here we go: If adding resistors in parallel decreases total resistance, why doesn't the voltage in the circuit change? Does the current increase to match ...
894 views

### Choosing the correct thermistor

I need help choosing a thermistor. I’m not sure what I need to look for. Let’s say I have this circuit measuring temperature: I have a range of temperatures from 0 to 10 degrees that I need to ...
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### Multimeter giving wrong current readings

I just got my first multimeter (TekPower TP8268) and I've been try to test it out, but I have been getting some strange readings with the current measurement. I have an AC adaptor to DC 12v and 5A. ...
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### Device with independent voltage and current

I have had some philosophical reflections about the voltage/current relationship. Assume we are somehow able to have a determined fixed current AND voltage on a device. This device could theoretically ...
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### What can the ohms of a DC motor tell me about itself?

I have a lot of motors and all type of size but mainly they are all small to mid size adult hand size or so , I took out my multimeter and switch to ohms settings and grabbed the ground and power ...
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### USB data serial termination resistors. Need them for STM32F2 micro? If so, what wattage?

I'm a little confused. The STM32F2 datasheet says only this, vaguely stated in the features: HNP/SNP/IP inside (no need for any external resistor) Is that referring to the D+/D- termination ...
164 views

### Determine supply voltage for led from current limiting resistor

Everyone knows how to calculate the resistance of a current limiting resistor for a LED but is it possible to go the other way? (aka determine the supply voltage from the resistor's value) I ask ...
421 views

### How does one determine the voltage of a node?

This sounds like a very straightforward question, and probably has an obvious answer. I've read a section in a physics book on electricity, I've read a textbook on DC and this simple concept seems to ...
490 views

### How do I calculate voltage on a multi-powered DC circuit where all ends go to ground?

I'm writing software that will calculate the correct voltage on each component, given the state that the DC system is currently in (ex. what power sources are on, what relays are open, fuses popped, ...
6k views

### Pull-down resistor ; why is it crucial

These 3 diagrams represent 3 test cases. Dia 1: When I perform an analogRead of analog port 0, then I get a high value obviously. According to the manual, the <...
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### Is Ohm's law required to calculate Watts?

A buddy and I were having a conversation. One of us is convinced that Ohm's Law and Watts are the same thing. After much research I can not find anything directly pointing Ohm's Law to defining Watts, ...
2k views

### Measuring the inductance of a coil?

I have a hand-wound coil I'm using in an LC Tank circuit. Using my multi-meter, I found out that the coil is drawing .6mA at 9v. Using Ohm's Law... $$R = V/I$$ $$R = 9/.0006$$ $$R = 15kΩ$$ Is there ...
18k views

### Voltage drop through a resistor using Ohm's Law?

I'm having a very hard time comprehending basic Ohm's Law. I was recently watching a video on the operation and use of Operational Amplifiers, and was completely lost because I couldn't understand ...
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### Powering a device by USB?

I would like to power a device via the 5V USB port on a computer, because I will also be communicating with the computer via the USB data cables. I know that USB ports provide 5V, but from what I've ...
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### Ohm's Law confusion — can there be voltage without current?

I know there has been asked a similar question about this before but I still have some issues to understand the whole voltage and current thing. ( Current without Voltage and Voltage without Current? ...
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### finding I(current)

I am learning about step response in RC and RL circuits and one of the problems i managed to redraw as the image above; however, when I am solving for i the answer is -5mA. I am just confused on why ...
877 views

### brief explanation of Ohm's law

How can I calculate ideal values of current for both short and open circuits by using Ohm's law. Further more usually said that it is not advisable to connect DC batteries of different voltages in ...