power loss is also equals to V*V/R, so, when the voltage is high, power loss should be high. but not??? why??

Question

i mean, why do we only consider I*I*R as a formula for power loss but not V*V/R. according to power , both the formulas represent the power loss. thank you in advance for the answers.

Answer 1

You're confusing the system voltage and the conductor voltage DROP.



The resistive losses in a conductor aren't affected by its voltage relative to some other conductor, only on the voltage difference across it.  This voltage difference is proportional to the current.  This is why high voltage systems have lower resistive losses:  they use lower currents for the same power, and the voltage difference across their conductors is smaller.

Answer 2

Either one is acceptable, it's just that current is generally more convenient to use in theoretical problems. They both give the same answer if you have the proper values for V, I and R.



EDIT: Oh if you're wondering about why we use transformers and all that (to get the voltage way up) it does have to do with those equations. You'll notice that if you can get a very high voltage (easy to do with AC) then you can actually increase the resistance to drop the power loss on the cables. Increasing resistance is much easier than decreasing it (which is what you have to do for I*I*R) so we prefer to use high voltages.

Now, you might argue, how can this be true if the I*I*R equation is also supposed to be true. The reason is because as you raise the voltage up through a transformer, you simultaneously lower the current (conservation of energy law), so that your I*I*R value becomes much smaller (and remains equal to V*V/R).

Answer 3

Ohms Law:

Power: P=IE ***"E" is used for "V"***

Voltage: E=IR

Current: I=E/R



Therefore algebraically it is true that

P=I*I*R and P=(E/R)*E



The P=V*(V/E) is rarely used because when in critical situation, the current (which is the amount of electrons flowing per second through a conductor) is factor whether it is a life or death situation. The higher the current, the more electrons moving through per second and the more danger a circuit pose. High current through weak conductors can cause fire. When shocked, the amount of current moving through the body determines whether the victim lives or die. So out of habbit and concern for safety the P=I*I*R formula is more commonly used.

Answer 4

i think,



the equation is,



total power=V*I

power loss=I*I*R



total power=power which is useful + power which is lost (in form of heat)



so when voltage is high (when power remains same..)

accordin' 2 equation VI current decreases ...



so accordin' 2 I*I*R when current decreases power loss also decreases......that's why power transmission is done on high voltage...



ref:gseb text book phy part-1 ch-4 example-6