# Current Density and Electron Drift Speed

## Homework Statement

The current in a 1.5 mm X 1.5 mm square aluminum wire is 1.10 A. What are (a) the current density and (b) the electron drift speed?

## Homework Equations

current density: J = I/A
drift speed Vd = J/ne

## The Attempt at a Solution

It's asking for an answer in MA/m^2.. when I divide I(1.1) by A(2.25 x 10^-6) I get 488,888.889. I tried the answer 489 and 488 and it says it's incorrect. Also tried 488,889 just to make sure.. still incorrect. Any help would be appreciated?

berkeman
Mentor

## Homework Statement

The current in a 1.5 mm X 1.5 mm square aluminum wire is 1.10 A. What are (a) the current density and (b) the electron drift speed?

## Homework Equations

current density: J = I/A
drift speed Vd = J/ne

## The Attempt at a Solution

It's asking for an answer in MA/m^2.. when I divide I(1.1) by A(2.25 x 10^-6) I get 488,888.889. I tried the answer 489 and 488 and it says it's incorrect. Also tried 488,889 just to make sure.. still incorrect. Any help would be appreciated?

Welcome to the PF.

When you say you "tried 488,889", you mean 488.889, right? Your answer looks correct to me.

SammyS
Staff Emeritus
Homework Helper
Gold Member
If the answer should be in mA/m2, then use 1.10 A + 1.10×103 mA.

Thanks for your replies. But it says MA/m^2, not mA/m^2. and the answer I've shared here does not work.. any other suggestions?

SammyS
Staff Emeritus
Homework Helper
Gold Member
0.489 MA/m2

so M is 10^6? ooh yea.. thanks!

SammyS
Staff Emeritus
Homework Helper
Gold Member
Ironic how a small thing like M vs. m can cause such a difficulty.

Ironic how a small thing like M vs. m can cause such a difficulty.

Here are the difficulties of Physics

- Units
- Signs
- Wording of the question
- Conventions