Curent densitys relation to drift velocity

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Homework Help Overview

The problem involves calculating the current density of a beam containing doubly charged positive ions moving at a specified speed. It is situated within the context of electromagnetism, specifically focusing on current density and drift velocity.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the calculation of current density using the formula J=I/A=nqv, with attempts to apply the given values. There are questions regarding unit conversions, particularly from cubic centimeters to cubic meters, and the implications of these conversions on the calculations.

Discussion Status

The discussion is ongoing, with participants exploring the correct unit conversions and their impact on the calculation of current density. Some guidance has been offered regarding the dimensional analysis and the relationship between volume units.

Contextual Notes

There is a noted confusion regarding the conversion of ion density from particles per cubic centimeter to particles per cubic meter, highlighting the importance of understanding volume relationships in this context.

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

ehild
 
im saying the conversion from cubic centimeters to cubic meters is 400
 
I got it thanks for all the help! WOOT
 

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