# 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.

331 questions
Filter by
Sorted by
Tagged with
11k views

### Why are resistor values constant in the face of changing voltage and current?

Small question, I see that resistors are labeled in certain increments (e.g 5, 10 50 Ohms), although a resistor outside of a circuit is completely without voltage and therefore current. Does this just ...
933 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 ...
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 ...
8k views

### Permanently dimming an incandescent light bulb

I have purchased a nice light bulb with long visible wires/resistors and plugged it in, on the ceiling. It burns too bright without a dimmer and does not look as intended (also the lifespan decreases)....
943 views

### Quick Question about ohms law and resistors

This may have been asked before, but I'm currently I'm an argument about whether or not passing 12v through a .1 ohm resistor would result in 120 amps due to Ohm's Law. (I=V/R) Providing that the ...
3k views

### 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 ...
5k views

### Ohm's law of a circuit which has both a voltage source and current source

The voltage source has a specific voltage through it regardless of the circuit's current and its resistance while the current source has a specific current through it regardless of the voltage through ...
544 views

274 views

### Is current calculation in copper wire for AC simple or not?

I'm trying to learn electronics by myself, and I'm starting with simple current calculations. Let's assume we have a straight wire of length L connecting a source and a sink. I know the voltage (V), ...
74 views

### Will the bright of the bulb increase or still the same in this simple circuit?

If Lamp2 is disconnected, What will happen to the brightness of the Lamp3? I think that the brightness will remain the same because Lamp2 is in parallel with the branch that contains Lamp3. Let's ...
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 ...
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 ...
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 ...
2k views

### Ohm's law clarification

I am slightly confused about Ohm's law. I understand V = IR, and I did a simple experiment on paper. The results are slightly confusing, so I was hoping someone could tell me if I'm right? First, I ...
48 views

### Circuit Analysis Involving DC Motors

When it comes to simple circuit analysis, there is millions of tutorials on how to analyze a resistor circuit, a RC circuit, or those involving LED the non-ohmic devices. However, I did not find a ...
76 views

### Measured amperage differs greatly from my math

I've got the following circuit: simulate this circuit – Schematic created using CircuitLab It works. The LED glows nice and bright. However my math doesn't match the readings I'm getting from ...
7k views

### Max Voltage for Speaker of Given Power Rating

I have been looking into the design of loudspeaker drivers and would like to know how to determine the maximum voltage which can be delivered to a given speaker. From Ohm's law we know that P = V^2 / ...
99 views

### High voltage, low current and vice versa

Can someone please explain to me in simple terms how is it possible to have high voltage and low current and low voltage and high current and what actually does harm to human body. Here is what I don'...
79 views

### Power adapter giving a specified current [duplicate]

I often see power adapters indicating 5V 900mA (or) 5V 1000mA or sometimes 5V 3.4 A. Obviously they are converting current coming from 220V/110V source to 5V DC using some step down converter. But how ...
100 views

### Help understanding circuit with diodes in it

I'm having trouble figuring out how this circuit works in the real world. I know theoretically the diodes should have a resistance of 0, 0 and infinite respectively, which makes the question quite ...
129 views

### Solving for current through a wire

This is a pretty simple question really and I'll feel embarrassed when I get the solution but its bugging me for now. The goal is to solve for I going from left to right. No values given for any of ...
491 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 ...
994 views

### 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 ...
161 views

### Ohm's Law vs. Conservation of Energy Misunderstanding

I am currently misunderstanding the relation between Ohm's Law and the law for conservation of energy. I am referring to the example (in the book "Foundations of Analog and Digital Electronic Circuits"...
90 views

### Struggling to understand series connections based on experiment

I'm having some issues understanding how series connections work based on an experiment I did at school. I took two lamps, and then connected them in series so the power initially goes to the first ...
2k 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, $P=\frac{V_s^2}{R}=2500 W$ (...
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 ...
118 views

### Maximum power/current for a battery?

I'm learning electronics and found this question below, which is exactly what I've been questioning myself. But there was no good answer there, so maybe someone here can help. Original question: ...
29 views

### Resistance/Voltage relation in Rheostat?

According to "How Computers Work" (Tenth Edition) by Ron White, he features a graphic of a potentiometer with three terminals on the bottom with the one on the left being for current flowing in and ...
164 views

### Fuel sender - need something to convert ohms to volts?

I need to connect a cars fuel sender(ohms) to a analog input on a GPS tracker (volts) Here's the catch, in our tests most fuel senders we worked with seem to send the data as ohms/resistance However,...
134 views

### Do I understand Ohm's law correctly?

I was reading a bachelor's thesis and it mentioned some technical details of a heated plate. Part of the technical details: MK2b Dual Power Technical Details  ...  Power Input: 12V or ...
848 views

### led resistor calculation, and resistor wattage?

I know this has been asked time and time again but bear with me as I am struggling to understand, so say I have this simple circuit here with 120v (dc for simplicity) as the input voltage and I have ...
298 views

### How are voltage dividers useful? I can't seem to get enough current for them to be useful

I must be doing something wrong here, because when I make my simple voltage dividers and do the math, the most current I could draw through my voltage divider would be 33.3mA. Here are my factors: ...