Ohms Law

Hello harjeetsinghengg

You are confusing yourself with your abbreviations for various standard items. (and I see that this a recent idea from where I am unsure)

Ohms Law has worked just fine for many years, and that Law still holds true today.

Ohms Law as originally stated shows:

W = Power in Watts

E = Voltage in Volts = EMF = ElectroMotive Force

I = Current in Amperes

R = Resistance in Ohms

and so on....

There is no contradiction at all, and I cannot see how you say there is a "contradiction with Ohms Law".

W = EI

W = E²/R

W = I² x R

etc....

Read more about Ohms Law here: http://en.wikipedia.org/wiki/Ohm%27s_law

Advise after reading that, if you are still confused, with

Kind Regards....

hi, thanks 4 ur valuable suggestion

will u plz clear this

we know V directly proportional to I

in transmission system to maintain same power at sending and receiving ends we increase V and decrease I, but both are directly proportional.

need ur clarification

we increase V and decrease I,

NO this is impossible!... In a transmission system at the 'sending' end you control the voltage and frquency.. It is the load at the 'receiving' end which determines what current is drawn.

Del

You must havnt read Sparkstation thread carefully.

I guess you are new student in a middle school, so has such a question.

its very simple. if you keep power constant, you have to increase voltage while reduce current proportally.

what change at present? have a think, of cause , its resistor! its no other than this resistor 's chnge that made power keep constant. otherwise, the power will be increase after voltage increase, at same time cureent will be increased as well.

pay more attation to your tearcher 's instruction in the class.

the similar question has also speed etc.

In transmission case, there is something that called "data" and "carrier frequency", the bandwidth of this freq is depend to voltage amplitude ( not the current ) and the data is depend to bandwidth of the carrier, as the higher voltage amplitude the bandwidth is high too, it use for reach a far place with out loosing any data that carried by frequency carrier.

To reach the proportional power and to make data save ( not lost for a far place ), so it must be increase the frequency carrier voltage and decrease the current.

I hope it can clear your problem.

There is no contradiction; you are mixing two distinctly different formulae! You refer to Ohm's Law, yet the equation you show (P=V*I) is is not Ohm's, but Joule's First Law.

Ohm's Law (E=I*R) relates the current through a circuit to the voltage impressed across the circuit.

Joule's First Law (P=E*I) relates the heat dissipated by a resistor to the current through the resistor.

A good discussion of the relationship between the two can be found here.

There is no contradiction. The want to maintain similar power levels on two different systems is not ohms law. To achieve it, however, you use Ohms law.

The missing component is the resistance. Do not confuse the power equation with ohms law. Write out the whole equation. You are comparing two volt system with a five volt system.

10 = 2 * 5 is actually "10Watts = 2Volts * 5Amps "

using Ohms law to find R;

E= I X R

2V = 5Amps X 0.4 Ohms

So if you want to maintain the same power levels of two systems with differing potential differences, you must change the resistance.

dont make a misunderstand his meanning.

he must hope to express this idea, from view of transmission system, why need so higher voltage transmit on line with small current throught it?

Thats why I said he hasnt read carefully spartstation's thread of 1

I can express again. if the power is constant, he must either increasing voltage reducing cutrent, or vice visa,

duo to increase voltage on line, and get in the result of currenet reducing, so that the loss power on the line will be reduced, too.

thats why !!!!

thats why our china develop so higher up to 1000KV line for transmitting elecgtric power.

Vote as a Good answser, quickly, ... who will get a profit from my threads. ...

haha, the more the best ...........

wow, its pity, so much good answer get back a off topic?

incridible?

haha

To the original poster... you must remember:

Resistance increases with distance in transmission applications.

I will leave it up to you to research the cross-sectional resistivity of the medium in your particular application.

That is why you must adjust your Voltage or current to satisfy Ohm's Law.

Of course, there's always the Edison Effect to take into consideration.

Ohm's law holds good.You have confused it by combining transformation with it.When we step up the voltage current has to reduce to maintain the same power.Stepping up is different and is through a transformer.So when u step up through a tranformer he circuit is different, resistance is also diffrent.For this again V/r =I will hold good.

but singhji that was a real googly.you bowled me.

thanx NESUBRA

but, I think ohm's law is applicable to all systems. It doesn't matter, where u r applying the ohm's law, it should prove right even in transformer.

that is not different ckt.

Hello harjeetsinghengg

When transformers are used, a different set of Rules apply, as for AC Circuits.

Now into AC Equations cometh these:

1. Winding DC Resistance
2. Windings Insulation Resistance
3. Bushings Insulation Resistance
   
4. Inductance
   
5. Interwinding Capacitance
6. Winding to case Capacitance
7. Hysteresis loss
8. Copper Losses
9. Phase angle alterations (Connection Vectors)
   
10. And more....

Enjoy the day.

Kind Regards....

It is applicable .But R in primary and secondary is the not the same.The linkage is magnetic between two windings.What I meant was Ohm 's law still holds good.Your surmise is that when we step up why current goes down .But circuit parameters as well other factors as explained adequately by spark station come in to play.best wishes

To use your terminology:

P=power

V=Voltage

I=Amperage

P=V*I

You are leaving out R=resistance

V=I*R

Raising resistance (R) will decrease amperage (I) for a set voltage (V).

Raising voltage (V) will increase amperage (I) for a set resistance (R).

You can not change amperage (I) without changing either voltage (V) or resistance (R) or both.

You have to look at both equations to get your answer. Not only power equals voltage times amperage but also voltage equals amperage times resistance.

To answer your question, you have to increase your resistance proportionately to maintain the same level of power if you increase your voltage.

Please correct me if I am wrong, but it appears you are dealing with power transmission & distribution design. We use transformers to solve the power transformation & manipulation issues.

Here is a basic standard power statement that should help clear the confusion.

Power In = Power Out

For example:

A "Step-Down" Power Transformer with 24,000 VAC primary input and 2,400 VAC secondary output mimics the following simple theory.

Primary Side Input Power: 24,000 VAC x 15 Amperes = 360,000 Watts or 360KW

Secondary Side Output Power: 2,400 VAC x 150 Amperes = 360,000 Watts or 360KW

As you can see the ratio is 1/1 and input power is equal to the output power. This example is for illustration only and is not entirely accurate as you must also factor transformer hysterisis losses (predominantly due to heating) and Power Factor into the equation.

There are several reasons for using higher voltages for power transmission. Some of which are: it allows the conductors used to be smaller and easier to work with while providing lower installation costs and the higher transmission voltage dynamics are less influenced by lightning and other ambient conditions.

The "Power-In" = "Power-Out" and Ohm's Law remain consistent when dealing with any voltage level device and are the basis of all electrical design criteria. You cannot change any one of the three factors (Voltage/Energy, Amperage, or Resistance) in Ohm's Law without affecting the power.

Hopefully this helps clear some of the confusion.

I'M CONFUSED!

Dude! You have posted several questions to CR4 requesting advice on (what appeared to be) design projects. Now you are stumped by Ohm's Law and fundamental electrical concepts?

My advice to you is to step away from everything that even remotely resembles electricity before you kill yourself or someone else.

To maintain same level of power you can either increse the voltage and decrease the current or vice versa.