• Support PF! Buy your school textbooks, materials and every day products Here!

HELP on electric field problem

  • Thread starter redhawks
  • Start date
  • #1
6
0

Homework Statement


A 2g plastic ball is suspended by a 2cm string in a uniform electric field of 1.0 x 10^4 N/C (the arrows point to the right)

a) is the balls charge positive of negative?
(B) If the ball is in equilibrium when the string makes a 15 degree angle with the vertical, what is the net charge. (15 degree angle going towards where the E arrows point)


Homework Equations


E=Ck((q1*q2)/r^2)

The Attempt at a Solution


a) i know it is positive
b) i did work but i can never get the right answer which is 5.3*10^-7C
 

Answers and Replies

  • #2
LowlyPion
Homework Helper
3,090
4
I'm not sure which direction your suspended object is going, but for b) consider the angle of the string. Won't it be the sum of m*g down and the electrostatic force horizontally? So isn't tan15 then the ratio of the 2 forces?
 
  • #3
6
0
its going right
 
  • #4
6
0
i dont understand. help, pleaseee
 
  • #5
LowlyPion
Homework Helper
3,090
4
i dont understand. help, pleaseee
So isn't tan15 then the ratio of the 2 forces?
F = q*E

and

q*E/(m*g) = tan15

q = m*g*tan15/E

Isn't that all there is to it?
 
  • #6
rl.bhat
Homework Helper
4,433
5
i dont understand. help, pleaseee
The force on the charged ball due to electric field is Eq, and weight of the ball is mg. The ratio of the forces is Eq/mg = tanθ. Solve for q.
 

Related Threads for: HELP on electric field problem

  • Last Post
Replies
3
Views
1K
  • Last Post
Replies
1
Views
918
  • Last Post
Replies
3
Views
6K
  • Last Post
Replies
2
Views
1K
  • Last Post
Replies
1
Views
3K
Replies
4
Views
2K
  • Last Post
Replies
0
Views
2K
Replies
33
Views
6K
Top