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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1 answer
1k views

What can cause a resistor to become non-ohmic?

Can anyone help me find some causes as to why a resistor may become non-ohmic? Thanks in advance.
1 vote
2 answers
10k views

What is the Danger in Plugging an 4 Ohm Speaker into an 8 Ohm Amplifier?

I know it is a commonplace warning not to plug in a 4 ohm speaker to an amplifier rated for 8 ohms. I am wondering what is the actual danger that is presented by doing this in an electrical sense. ...
0 votes
1 answer
40 views

Power up a motor/pump

I have a pump (6-12V 4-5W) that i want to power up with a generator (9V 1.5A). I've calculate the current needed with : I = 5W/8V = 0.55A. Next i've calculated the resistance needed : R = 9V / 0.55A =...
3 votes
3 answers
11k views

If the voltage at ground is 0, why is there current flow?

From what I understand, voltage is required to motivate electrons to flow through a circuit. With KVL we have that the voltage will essentially be depleted at the return point (ground). So, if this is ...
1 vote
1 answer
1k 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 ...
0 votes
1 answer
140 views

What is the current flowing through the resistor in this circuit?

I have to find the current flowing through the resistor connecting node a to d. I know it's a current divider problem, but I'm having a hard time finding the correct expression. I presume R5 is ...
15 votes
7 answers
9k views

Ohm's law doesn't seem to be working for this electric motor

I'm a beginner in this field so please forgive me if I'm confusing with my question. There is a component that I can't understand with Ohm's law which is a washing machine drain pump. Washing machine ...
0 votes
6 answers
1k views

Smallest possible resistance (highest current) [duplicate]

I'm new to electronics and I've been familiarizing myself with some basic formulas, specifically Ohm's law. It seems to imply that if resistance is smaller than 1, let's say 0.00001 Ohm, then I can ...
0 votes
1 answer
178 views

What’s wrong with my resistance calculations?

I was trying to use ohms law, and there is something I don’t understand. There is a blender that uses 240v at 0.25 A. 240 / 0.25 = 960 ohms However, when I tested the appliance with a multimetre, it ...
2 votes
6 answers
2k views

What is the voltage potential of ground during a short

During a short, is it possible for the voltage potential of the ground to change? Say for example, we short a 9V battery, how does the ground stay at 0V and not become 9V?
-3 votes
3 answers
224 views

Is it possible voltage without current and opposite [closed]

I got really surprised by seeing this possibilities from a power, energy calibrator is it really injecting it by violating the laws what we use in practice? See the photos? If anyone knows it please ...
2 votes
4 answers
261 views

How is it possible to have high voltage that is safe?

I am aware that current is very dangerous and only 0.2 amps is enough to stop a heart. However I always see that high voltage is dangerous. Tasers produce a high voltage but since there is low current ...
3 votes
1 answer
360 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 ...
2 votes
4 answers
572 views

Circuits explained without analogies [closed]

So, I am trying to fully understand circuits without the use of analogies like "voltage is like a waterfall" or "a battery is like a pump," since I've heard that those analogies break down when we get ...
0 votes
4 answers
531 views

What is voltage exactly? [duplicate]

First, let me start off by saying that I have read the answers to this question (which is the same as mine), but the answers basically explain the different ways voltage is created or compare it to ...
1 vote
4 answers
4k views

Why are voltage and current directly proportional? [closed]

So, I thought I had an understanding of Ohm's law, but after thinking deeply about it, the direct proportionality between voltage and current doesn't make a lot of intuitive sense to me. So, when I ...
0 votes
5 answers
358 views

Beginner Question about the logic behind Ohm's Law?

In all the physics i learned and practiced many subjects But understanding Ohm's law used to be a big problem for me... Here is what i mean : We have a 5 volt battery. And a 3 volt/ 20 mA led. So ...
6 votes
3 answers
3k views

With parallel termination of a transmission line, why does the receiver see the full voltage?

With parallel termination of a transmission line, the line characteristic impedance \$Z0\$ is matched with the pull-down resistance \$Rt\$. But, in that case, shouldn't the receiver see half of the ...
0 votes
2 answers
911 views

Finding the value of a specific resistor

Let say you have a network of resistors. All resistors have values but one of them is labeled "R" Given the value of a total voltage and a total current, find the value of R. My head start would be ...
8 votes
2 answers
7k views

How a DC motor works when connected to a power supply but no resistor?

I connected a 12V DC motor to a battery of 12V only. The motor rotated perfectly fine. But my question is that if you don't have a resistor attached to the circuit, as per theory the current is ...
0 votes
3 answers
471 views

how does ohms law apply in power system

It appears that either all the people over the internet have either not thought about this question or that I am mistaken in my thought somewhere: Confusion appears when I try to apply ohms law to ...
7 votes
3 answers
2k views

Amps / current doesnt add up to the expected figure - Ohm's law failure on my part!

Can anyone offer suggestions as to where I am going wrong please? In my circuit (diagram below) the system voltage is 12.03 V and the lamp resistance is 2.9 ohms (measured with power disconnected ...
1 vote
1 answer
69 views

Creating a small range, small baseline varying resistor

I am doing a design project on making a passive varying resistor device. I have a flex sensor that increases in resistance when you bend it. It has a 10k ohm nominal resistance and increase to 110k ...
1 vote
1 answer
116 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 ...
-2 votes
5 answers
364 views

Ohms law and voltage

So Ohm's law says I=V/R pretty simple, say I had a 5 volt source and a load I wanted to limit to 20 mA, so I would use a 250 ohm resistor which would limit the current to 20 mA at 5 volts. (I'm ...
0 votes
1 answer
60 views

Wattage of DC device is not equal to AC [closed]

I have a led driver (LPC-20-700) that is 30V and 700mA, which makes it 21W. I run 10 leds (≈ 2.8V drop) in series with it and it is an constant current device. If I plug my multimeter between, I do ...
8 votes
3 answers
2k views

Why is my circuit's current far lower than expected with 2.6v / 220Ohm / and LED?

I have a very simple circuit which I have measured the current to be only 3mA but should be in the range of 18mA. I have a simple circuit using 2 AA batteries (NiMH) at 1.3V each in series for a total ...
25 votes
7 answers
94k views

Why do we need resistors in led

I've researched and it says that resistors limit the current flowing through the LED. But this statement confuses me because we know that in a series circuit, the current is constant at every point, ...
-1 votes
2 answers
3k views

Does resistance of carbon brushes in DC Motors decreases after couple of uses?

I know that after couple of uses DC Motors we should replace carbon brush because the physical size of carbon brush will be reduced and it can not do its job! But let me ask my 3 main questions.... ...
0 votes
2 answers
185 views

Calculating resistance when ohm law has no response

I have a 3v DC source and a 3v light emitted diode, i want power this led with just 5 mA . There is a formula : R = V/I But in my case V is 0 V[source] - V[LED] = 0 So R is 0 always!!! How can i ...
0 votes
1 answer
142 views

Add a LED and a resistor to a working circuit

We found, with my 6 y.o. kid, a 9V battery and an old CPU fan power supply fan, and we were happy to see the following circuit 1. working. Then he asked: "Can we add a switch and a LED?" For sure we ...
1 vote
2 answers
158 views

How do voltages at outputs drop as current increases?

As I looked at some 74xxTxx ICs, such as this simple NAND gate, I noticed that the minimum \$V_{OH}\$ decrease as current flowing from the outputs increase. But, from my understanding of Ohm's law, \$...
0 votes
1 answer
179 views

Why the resistors needs higher Ampers if the Total current is 4 Ampers?

I have a question about the circuit as shown up. My question is if the total current is 4 Amperes, why do the resistors need a higher current? Am I missing something? If that so, what it is?
2 votes
6 answers
2k views

General definiton of Ohm's law

There has been some disagreement lately on whether a diode follows Ohm's law or not: Does a diode really follow Ohm's Law? Specifically things like However, the truth is the resistance of a ...
0 votes
2 answers
1k views

How to apply Ohm's Law correctly to a circuit?

Ohm's law continually confuses me in my attempts to use it. Right now I'm trying to supply a maximum of 800 mA by 1.5 V from a 5V source. Does that mean that I need a 1.875 Ohm resistor ...
0 votes
1 answer
63 views

Is my wire rated at a high enough current?

I am in the process of planning a speaker build. I am making sure my current wiring is up to the demands of a new system. The amplifier is a CV 1800, which can put out 9.5 amps at 4 ohms in stereo (...
2 votes
2 answers
5k views

Why doesn't current increases when the voltage is increased

When connecting two batteries in series the voltage is increased. For example: Connecting two 5V batteries in series will produce 10V voltage but the current will be the same. According to Ohm's Law <...
0 votes
0 answers
108 views

Solving a circuit with node voltage method

I have the following circuit: Knowns: Iz = 80 mA R1 = 100 Ohms R2 = 150 Ohms R3 = 220 Ohms R4 = 330 Ohms R5 = 100 Ohms As I understand Gi stand for the current source internal conductivity, but ...
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3 answers
6k views

Do I need a resistor between my battery and servo?

I'm trying to better understand Ohm's law as it relates to general microelectronics projects by taking a simple project I'm working on now. I have a 9V battery powering a small tower pro sg90 servo. ...
7 votes
1 answer
11k views

Joule–Lenz Law.. Forgotten history? [closed]

We are all, or should be, extremely familiar with this graphic. It is course the magic triangle used to represent Ohm's Law. We should all also be very familiar with the similar power triangle. ...
1 vote
3 answers
3k 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 ...
3 votes
3 answers
737 views

How to calculate current on different resistors

I hope this is not a wrong place to ask. I've just started studying electrical engineering and I have (a newbie) question and would really appreciate it if you guys could help me. So I have this ...
7 votes
7 answers
10k views

How can 4 resistors of 30ohms each be connected so you end up with a resistance of 18ohms?

An association of 4 resistors of 30ohms each, how can one assemble them so you get a resistance equivalent of 18ohms?
1 vote
5 answers
1k 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 ...
0 votes
1 answer
362 views

Using Nodal Analysis Method

Question: I had solved easier circuits problem using nodal analysis but this one it has supernodes on nodes 2 and 3 which I find it difficult solving. thus I need help as I am trying my very best to ...
1 vote
3 answers
332 views

Why voltage is the same after placing a resistor?

simulate this circuit – Schematic created using CircuitLab Hi. I'm testing a very simple circuit with a multimeter. In Ohm's Law, a resistor should affect the voltage, but in my circuit it ...
0 votes
1 answer
191 views

How many amperes without resistance?

For the below circuit according to Ohm's law the led will get 23mA. What happens if the resistance is removed? How many amperes will the LED get? My assumption is that the wire has some kind of ...
0 votes
2 answers
2k views

Current Flow into MCU pin

If I have an MCU, e.g. ATTiny85, and I connect a 5V source to a pin on the ...
0 votes
2 answers
7k views

Calculating current in a series circuit

Given the following circuit, it seems like we could use ohms law to conclude that current = voltage / resistance. With a source voltage of 3.3 and a resistance value of 220, current = 3.3 / 220 = .015 ...
0 votes
2 answers
92 views

Finding the heat dissipation but calculations not going right?

I am trying to find the heat dissipation from a 20000 V 1 A filament which is on for 1 second. I just randomly came up with this to try to test my understanding of joules first law and ohms law with ...

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