# Equation of resistance

1. Apr 7, 2012

### sreerajt

Voltage(V) is proportional to current(I). And so V=(a constant)*I. That constant is known as resistance(R), where R=V/I. Why can't we write that I proportional to V and then write R=I/V??

2. Apr 7, 2012

3. Apr 8, 2012

### Staff: Mentor

We write G=I/V
and the units of G used to be known as mhos (that's Ohms spelled backwards) with symbol an upsidedown Ω (omega).

Nowadays, the units have been renamed an uninteresting "siemens".

4. Apr 8, 2012

### Sefrez

Because that is not the reality? I know VR != I. If that were the case, current would increase with resistance. Which completely disagrees with our current definition of resistance!

EDIT:
Oh, I misinterpreted your post. Well, yes, of course you could. But R would be a different quantity, as the right side of the equation implies.

Last edited: Apr 8, 2012
5. Apr 12, 2012

### sreerajt

Could you please make it clear???

6. Apr 12, 2012

### f95toli

Resistance (R) is DEFINED to be what it is. There is no "reason" for it, it is just a convention.

And again, the quantity I/V already has a name of its own: conductance (G), which has the units of Siemens.

7. Apr 12, 2012

### sophiecentaur

I think you means 1/R.

Remember: R is 'how hard'
and G is 'how easy'.

8. Apr 12, 2012