# Resistance or current

1. Apr 25, 2015

### gracy

Should not there be R (resistance) instead of I (current)in the last line i.e
I ∝ m/a^2

2. Apr 25, 2015

### Staff: Mentor

Probably.

3. Apr 25, 2015

### XZ923

If this is an electrical question, there's something missing from that final line....

4. Apr 25, 2015

### gracy

Yes,It is.

5. Apr 25, 2015

### gracy

What's that?

6. Apr 25, 2015

### XZ923

I'm trying not to just give it away. Here's a hint: review Ohm's Law

7. Apr 25, 2015

### Staff: Mentor

It is a "proportional to" sign in the last line. It is a weird way to express the proportionality, however.

8. Apr 25, 2015

### XZ923

Very true; I'm just not a fan of expressing a current-to-resistance proportionality without a requirement that "voltage remains constant".

To better answer the OP's question:
Assuming voltage remains constant, resistance and current are inversely proportional to each other
Assuming the physical makeup of the conductor remains the same, cross-sectional area an resistance are inversely proportional to each other
Therefore, assuming voltage and physical makeup of the conductor remain the same, current and cross-sectional area of the conductor are directly proportional

9. Apr 25, 2015

### sophiecentaur

There's something I am not getting about the OP. The symbol ρ is commonly used for Resistivity and also for Density. It strikes me that the two appear to be used interchangeably in the attachment. I don't see the logic of the argument being used in that attachment. Can someone explain. please?

10. Apr 25, 2015

### nasu

Maybe she can provide more context. Is that from the internet?
Without context looks like a bizarre relationship.

They seem to use d for density and ρ for resistivity.

11. Apr 26, 2015

### sophiecentaur

@gracy
It is often possible to take two unrelated expressions, then re-arrange them, algebraically, assume that some of the variables in each expression are the same value and get an unexpected apparent relationship between two variables. It can be mathematically correct but of no meaningfulness in terms of the Physics at work. One needs always to be aware of the physical implications of such bits of maths manipulation.