Curent densitys relation to drift velocity

[DODGEVIPER13]

Homework Statement

A beam contains 4.0x10^8 doubly charged positive ions per cubic centimeter, all of which are moving north with a speed of 1.2x10^5 m/s.

(a) What is the magnitude of the current density ?
(b) What is its direction?
(c) What additional quantity or quantities are needed to calculate the total current in this ion beam?

Homework Equations

J=I/A=nqv (v = drift velocity)

The Attempt at a Solution

Well I tried this (4.0e8)(2)(1.6e-19)(1.2e5) which I thought would give what I wanted but apparently not. I was thinking by looking a dimensional analysis that it has something to do with the seconds in the velocity but I am not sure?

 

[ehild]

Take care with the units of length. The ion density is given in particles/cubic centimeters, the velocity is given in m/s. The current density has to be in C/m².

ehild

 

[DODGEVIPER13]

Ok I did that I converted (4e8) in particles/ cubic centimeter to 400 particles per cubic meter but it still did not give the right answer?

 

[ehild]

There are 400000000 particles in one cm³. How many cm³ makes one m³? (which one is bigger? 1 cm³ or 1 m³?) Where are there more particles? In a big volume or in the small volume?

ehild

 

[DODGEVIPER13]

Huh wait your confusing me I though 400 cubic meters was correct is it not?

 

[ehild]

What was 400 cubic meters?

ehild

 

[DODGEVIPER13]

im saying the conversion from cubic centimeters to cubic meters is 400

 

[DODGEVIPER13]

I got it thanks for all the help! WOOT