Surface charge density problem

  • #1
1. A spark occurs at the tip of a metal needle if the electric field strength exceeds 4.00×106 N/C, the field strength at which air breaks down. What is the minimum surface charge density for producing a spark?



2. surface charge density = Q/A



3. The answer is 3.54*10-5 C/m2. How was this obtained? I couldn't figure out by playing with dimensions...
 

Answers and Replies

  • #2
lightgrav
Homework Helper
1,248
30
Gauss' Law ...
Starting with Coulomb's kQ/r^2 = E , move the r^2 over with the E .
... x 4 pi , and it looks like the E-field is spread over a surface surrounding 4 pi kQ :
=> E.A = 4 pi k Q ... E has to pierce the Area A , which has to enclose charge Q
 
  • #3
I don't understand. E*A = 4pikQ but you don't know A or Q...
 

Related Threads on Surface charge density problem

  • Last Post
Replies
17
Views
4K
  • Last Post
Replies
1
Views
675
  • Last Post
Replies
11
Views
2K
  • Last Post
Replies
4
Views
2K
  • Last Post
Replies
3
Views
2K
  • Last Post
Replies
11
Views
991
  • Last Post
Replies
12
Views
12K
  • Last Post
Replies
2
Views
2K
Replies
1
Views
1K
  • Last Post
Replies
1
Views
11K
Top