Question

Is V directly proportional to I (From V=IR)??

Answer 1

First of all, I is proportional V according to the Ohm's Law. R is merely a constant you need to obtain an equation. However, it is true that R changes with temperature and pressure, therefore Ohm's Law is only applicable in an invariable environment. Also this constant R is different for different materials.

So, do not get confused.

Ohm's law is not a universal law, please remember that as well. Some materials do not follow it and we call them non-ohmic conductors. I hope I helped! ^-^

Answer 2

This question relates to how electricity is transmitted on various NATIONAL GRIDS. AC is used, partly because it can be transformed using a transformer. To get the electricity or maybe I should say the electrical POWER from A 1000 miles to B, if it were transitted at 250 V then the actual CURRENT needed in the line would be very high. That would cause problems in the cables, one of which would be heating. So, the voltage is stepped up to say 2500 V and v possibly more. Then the current going down the transmission lines is less, but the power transmitted is the same. At the B station, the AC is transformed from the 2500V transmission voltage back down to the commercial/domestic voltage of 250V. Then the current required can be drawn, 'cos the power has "got there".