Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points. Introducing the constant of proportionality, the resistance, one arrives at the usual mathematical equation that describes this relationship:
I
=
V
R
,
{\displaystyle I={\frac {V}{R}},}
where I is the current through the conductor in units of amperes, V is the voltage measured across the conductor in units of volts, and R is the resistance of the conductor in units of ohms. More specifically, Ohm's law states that the R in this relation is constant, independent of the current. If the resistance is not constant, the previous equation cannot be called Ohm's law, but it can still be used as a definition of static/DC resistance. Ohm's law is an empirical relation which accurately describes the conductivity of the vast majority of electrically conductive materials over many orders of magnitude of current. However some materials do not obey Ohm's law, these are called non-ohmic.
The law was named after the German physicist Georg Ohm, who, in a treatise published in 1827, described measurements of applied voltage and current through simple electrical circuits containing various lengths of wire. Ohm explained his experimental results by a slightly more complex equation than the modern form above (see § History below).
In physics, the term Ohm's law is also used to refer to various generalizations of the law; for example the vector form of the law used in electromagnetics and material science:
J
=
σ
E
,
{\displaystyle \mathbf {J} =\sigma \mathbf {E} ,}
where J is the current density at a given location in a resistive material, E is the electric field at that location, and σ (sigma) is a material-dependent parameter called the conductivity. This reformulation of Ohm's law is due to Gustav Kirchhoff.
Find the supply voltage of a ladder circuit shown, so that I=7A. Assume R=11Ω. (The unit must be placed)
Hello, everyone. Please, help me with this. Could someone explain to me how to solve such tasks. I literally spent the whole day watching Khan Academy and trying to figure out how to solve...
It's ABCD question with answers attached.
Problem is that, I don't think that neither of those are correct. From KVL the equation seems to be i = (E2-E1)/(2r1+2r2 + R). I've attached images of the circuit, answers, and my solution.
Can someone please point me if I am wrong, and if yes, where's...
Here is the actual question.
And here is my attempt at a solution
In Summary I did the following
Found the Equivalence Resistance to Be 5.9 ohms and the Current throughout the entire resistor to be 1.53 Amperes
Worked backwards from my resistor simplifications. When the resistors were in...
Hello everyone new here :)
I've recently enrolled myself in a computer technician course and I've encountered a few (basic) electrical sums.
I have absolutely no electrical background, and the course mentioned no requirement of such, but I'm already being presented with work I have no idea of...
Homework Statement
The following circuit is given, and all voltage, current, resistance and power must be found for each resistor.
I have found the following information:
Vsrc = ?
Isrc = .5A
Rsrc = ?
Psrc = ?
V1 = ?
I1 = .5A
R1 = ?
P1 = ?
V2 = 2.5V
I2 = .25A
R2 = 10
P2 = .625W
V3 =...
Homework Statement
Homework Equations
Vf+(Vi-Vf)e-t/RC
Tau = RC
The Attempt at a Solution
[/B]
Normally, I would use the eq'n mentioned above to find Vr in an RC circuit. However, this second capacitor is throwing me off. Is there a new equation I should use? How do I think about this...
Homework Statement
Two cells of same emf E and different internal resistance r1 and r2 are connected in series to an external resistance R.The value of R for which the potential difference across the first cell is zero is given by
(A) R=r1/r2
(B)R=r1+r2
(C)R=r1-r2
(D)R=r1r2
Homework Equations...
Homework Statement
I have to write about voltage within a parallel circuit and the formula for voltage in parallel is Vt=V1=V2=V3. But I was wondering if that's only the case if the resistors have the same resistance becasue I used resistors with different values
Homework Equations
V1=V2=V3...
Homework Statement
hello, just came across this type of question for first time.
A voltmeter with a range of 0-30volts is to be used to measure a 120 volt circuit. calculate the value of the resistor to be placed in series with the meter. the sensitivity of the meter is 1000 ohms per volt ...
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Two lightbulbs in series, one with 50W one with 100W which is brighter. I have two different solutions and can't see my error. Using PR=V^2 and I^2=P/V 50/√50R1=100/√100R2 with the same current and R2=2R1. Using PR=V^2 and the same voltage across both bulbs yields 50R1=100R2 or R1=2R2. Which...
Homework Statement
A pair of power transmission lines each have 0.68-Ω resistance and carry 650 Amp. If the primary voltage of the 10:1 step-up transformer is 4.6 kV, calculate the input voltage of the step-down transformer at the other end.
Homework Equations
P=IV
V=IR
IpVp = IsVs
The...
Hello.
Resistive Ohm's law is famously known as V = IR. We can derive its microscopic version as being followed.
V = El, where E and l are, respectively, an electric field and a resistive load length over which a voltage drop V is developed.
I = JS, J and S are a current density and a...
Homework Statement
The circuit of the given problem is attached to this post (jpg file). All info is given in the photo.
Problem: find VA, VB, IA.
Homework Equations
Ohms law
KCL equations
P = VI or V^2/R
The Attempt at a Solution
- First, I noted that VB = 9 - VA.
- next, i set up a KCL...
Homework Statement
I'm trying to find the voltage drop V1 of the following circuit, assuming Vin=1v, and for the life of me can't seem to get the right answer.
Homework Equations
KCL, Ohm's law
The Attempt at a Solution
I basically tried to use KCL at the top node,
Vin/2+2V1 = V1/3 +...
I have a DC powered pump, that has suddenly stopped working.
During troubleshooting I came up with the following results, that I just cannot reconcile:
Input wires, not connected to pump: 12v
Input wires connected to pump: 0v
Sounds like a short in the pump right? However, connecting the...
hello i was wondering about how a dc motor would work as a generator and how the voltage and current would scale with ohms law. for example let's say i had a 350 watt motor that's 36 volts and generates 9.72 amps now let's say i use that motor as a generator but only generate 200 watts how would...
Hi Guys
I'm new the PF and hope I'm posting I the correct place, apologies to admin if not ;-). I'm working on a project at home and maths is not my strong suit. I have an equation that I need to complete and involves converting thermal heat capacity in water into electric power. From what I...
Homework Statement
In the following figure, R1= 3.1 Ω, R2= 4.9 Ω, L1= 0.155 H, L2= 0.2 H and the ideal battery has ε = 5.6 V. Just after switch S is closed, at what rate is the current in inductor 1 changing?
Homework Equations
{ \varepsilon }_{ induced }\quad =\quad L\frac { di }{ dt } \\...
Hey guys, hopefully this is the right subforum..
Anyways, I am wondering how to read the ratings of a relay. Here is what I am looking at:
http://www.ebay.com/itm/5pcs-5V-T73-SRD-5VDC-SL-C-5Pin-10A-Relay-Module-Arduino-ARM-PIC-AVR-DSP-/161755474571?pt=LH_DefaultDomain_0&hash=item25a960aa8b...
Homework Statement
Homework Equations
Current = Voltage / Resistance.
The Attempt at a Solution
I know this requires me using the formula Current = Voltage / Resistance, but I'm confused to which measurements I use. I think possibly I take 0.9 from 5 volts then do 4.1 / 10000?
Homework Statement
A student is calculating the resistance of a piece of fuse wire. He takes 5 readings on the voltmeter and ammeter for different settings of a variable resistor.
He decides that instead of measuring the gradient of the graph to calculate the resistance, it would be okay to use...
Homework Statement
Hello.
The resistance of a wire increases when the temperature increases.
How would this cause the shape of the graph to change? Explain why. The graph shown is a straight line graph with the line traveling at 45 degrees path. The x-axis is VOLTS. The y-axis is CURRENT...
Homework Statement
http://i.gyazo.com/c6b73ca3a53b7d36bce59a0aa5009d27.png
Homework Equations
Kirchhoff's Current and Voltage Laws, Resistors in parallel and in Series.
The Attempt at a Solution
The main thing confusing me is the diagonal 6 Ohms, not too sure what it is parallel too and how...
Is ohm's law (V=IR) works for both AC and DC. PLz explain in details
Also let me know which formula is right for power calculation for AC and DC circuits. (P=VI or P=VICos)
Does anybody understand the fundamentals of what is happening in this circuit?
Tungsten welding info is all about high current... but this is a low current scenario.
AC input, CDI Coil generated 20Kv (estimated) suffers voltage drop over 100mm of tungsten rod.
The larger the diameter... the...
Hi, i didnt know where to put this question cos its kind of multitopic, here is why...
I am working on a better way to take mechanical energy from muscles, i made a teste bench for pedalling in very different ways, including traditional(circular) pedalling, the thing is. I am measuring the power...
At high school we were taught basic circuit formulas such as V=IR, P=IV etc but now I am studying circuits in Engineering (at university)
we have been introduced to the techniques of nodal and mesh analysis.
My question is, when and why do we use these techniques rather than the...
Homework Statement
Using all the following resistors : 2 x 12 ohms , 2 x 24 ohms , and 2 x 36 ohms. create a circuit where the total resistance will be 4 ohms.
The problem states that I have to use ALL of the resistors..making it so complicated
Homework Equations
1/Req = 1/R1 + 1/R2...
I have a solar cell that is rated 3.6 amps .5 volts 1.8 watts when you take a ammeter it does put out 3.6 amps, but this is basically a dead short reading. What I want to know is these cells put out .5 volts using ohms law how much resistance is needed to have a voltage output of .3 volts so you...
I recently learned that ohms law is not always obeyed. I found this surprising because I thought ohms were defined in terms of volt and amperes by the equation R=V/I. I did a little googling and found the following definition...
This clarified things a little in that the definition of an ohm...
We have all seen Ohms law, J=σE. This approximations makes sense in simple electric fields in which the charges are accelerated in parallel.
However as I will demonstrate, this implies a few conditions on the charge density (ρ) associated with the current density (J).
Now, from the continuity...
Look at the attached problem with solutions. I don't understand what the author means in c) when he says that succesive shells contribute less and less because the cross sectional area grows proportional to r2. The flux through a closed surface is always the same (Gauss' law). Rather the reason...
Here is my question: When I look a p.d divider circuit I get slightly confused, because the way I was reading the explanation it says: that when the a thermistors has 0 resistance it has 0V across, so when the resistance increase the voltage increases and the will turn on the base emitter to...
Does Ohms Law have practical limits?
For example:A piece of steel wire of length of length 10um and of CSA 20E-10.
Can we calculate the resistance of such a tiny piece of wire (resistor) in the usual way?
thanks
Hello, I am trying to get my head around biasing.
I do understand the principles.
In the attached circuit the Collector current is 2.5mA and the collector resistor is 1K. Therefore my circuit here is biased at 2.5V. The power supply is 5V.
So that would give a 2.5V drop over the collector...
1. Write the equation for each run in the form (potential=constant x current)
{the form has two numerical list to work with}
2. How do I find the constant from these 2 lists? Is it the correlation that the question is looking for? or, Is it OHMs constant, that the question is talking about??
A colleague and I are looking at modelling a hot electron beam hitting a initially charge neutral plasma. Initially we're looking at the 1D problem, the equations we're using are:
\begin{array}{rcl}
\gamma^{3}(v/c)\left(\frac{\partial v}{\partial t}+v\frac{\partial v}{\partial x}\right) & = &...
Homework Statement
See picture.
Homework Equations
Ohms Law-V=IR
The Attempt at a Solution
i do not know what to do once i find Rt (8.714...) because there is a parallel and a series in this circuit...
I think what I am doing is pertaining to ohms law but I'm not sure because we're not suppose to rely on equations or literal physics terms, but when we learned from previous labs. So this is mostly conceptual and I want to make sure I'm thinking through this correctly.
Diagram 1...
I've never really understood the relationship between voltage, current, and resistance. The more I read about them, the less comfortable I feel discussing them. V=IR...mathematically, it doesn't get any simpler than Ohms Law, yet when I try to predict the behavior of its variables in real world...
Thermistor Temperature- Ohms Law??
Hi All!
I am trying to convert a current of 795mA to a temperature in degrees celcius but I don't understand how to do it.
I realize that Ohms law of V= A/ R is involved somehow but that's the extent of my knowledge.
PLEASE HELP!
I have also been...
i have attached a picture showing the problem;
just wanting to know if my working out and reasoning is correct please.
http://img29.imageshack.us/img29/5412/questionsq.jpg [Broken]
The Attempt at a Solution
i have used KCL to answer (a) and (b) and have answers 0.6 and 1 respectively.
for (c)...
What does increasing the frequency of a computers main bus [the bus that connects the CPU to the chipset] imply about the voltage ["information"] traveling on a bus? (what IS the frequency of a bus effectively measuring, data units per second?)
The way i see it (please correct me if I'm...
can someone please explain to me physically how is it that
when i have an AC source and i measure Voltage on a resistor its the same with and without the resistor
and when i have a DC source and i measure Voltage again on the resistor and now there's a different reading
its like ohm law...
Hello
I'm trying to get my head around ohms law, and have a question.
If I have a motor that draws 12volt 100amp, and I would like to drop the amps down to 30, would I put a 360ohm resister in line.
12 * 30 = 360
V * I = R
Side note can you get a resister that is 480 watt...
Probably a simple question for electrical people, to which I never picked up the answer in my studies. I know I'm missing something simple, or just thinking about it the wrong way.
A transformer increases voltage, and decreases current. And yet...Ohms law states that higher voltage results...