Electric field strength -- calculating distance from charge

  • #1

Homework Statement


At a distance D from a very long (essentially infinite) uniform line of charge, the electric field strength is 1000 N/C. At what distance from the line will the field strength to be 4000 N/C?

Homework Equations


E=kq/r2

The Attempt at a Solution


I know that E is inversely proportional like so: E~1/r2
hence by rearranging for 'r' I got: r~sqrt(1/E)
then I plugged in 4E because 4000 N/C is four times 1000 N/C: r~sqrt(q/4E)
and I got r~E/2 but the answer is E/4 and I don't know how?

Thanks in advance
 

Answers and Replies

  • #2
BvU
Science Advisor
Homework Helper
13,880
3,432
HI,

You want to develop an expression for the electric field of a long line charge first. Your relevant equation doesn't fit that.
 
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  • #3
Fab
What is the relevant equation that fits this scenario then?
 

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