# Colulomb's Law?

1. Dec 11, 2003

### mustang

Problem 3.
Two identical conduction spheres are placed with their centers 0.34m apart. One is given a charge of +13*10^-9 C amd the other is given a charge of -14*10^-9 C. The spheres are connected by a conductiong wire.
After equilbrium has occured, find the electric force between the teo spheres. Answer in N.
Note: Would you add up the charges divide by two and the put it in Colulomb's law were it is the charged squared? From there find the electric force?

Problem 9.
Three point charges , q_1=+6.6 uC, q_2=+2.4uC, and q_3=-2.4uC, lie along the x-axis at x=ocm, x-2.4 cm, and x=5.3 cm, respectively.
a. What is the force exerted on q_1 by the two charges? (To right is positive) Use 8.99*10^9 N*m^2/C^2. Answer in N.
Note: How would put these values in Coulomb's law?

2. Dec 11, 2003

### himanshu121

yes for first part

Find the field at the point q1 due to q2 & q3 sayit is E

Then force will be q1E

3. Dec 11, 2003

### Chi Meson

re #9:

remember that E is a vector. THe "+" and "-" values that you get with Coulomb's equation do not tell you the direction is to the right or to the left. Draw a picture for E from q2 and from q3. IF they point in the same direction then the two E's add up. IF they point in different directions, then you subtract values, and the direction of the net E is the same as the larger E.

4. Dec 11, 2003

### himanshu121

From Couloumbs law u can calculate the direction

the Vector form for Coulombs law is

$$\vec F = \frac{kq_1q_2}{\vec r^3} \vec r$$

The thing is u have to put the sign of q1&q2 along with magnitude

Last edited: Dec 11, 2003
5. Dec 11, 2003

### mustang

regarding question 9

To find magnitiude of the force of q_1 don't I use Coulomb's law twice. Once with the second charge to be 2.4uC and another time with second charge -2.7uC, with both charges being multiplyied with 6.6uC.
Then I will get two amounts whih i would multiply with what?

6. Dec 12, 2003

### himanshu121

I was just giving the formula in vector form

U got it right u will have to do with charges

Got the force due to both charges say F1,F2

Apply the superposition Net force= F1+F2

Note you have to add vectors force is vector

7. Dec 12, 2003

### mustang

8. Dec 13, 2003

### himanshu121

U never get such an enormous force generally in Coulombs law or in Electrostatics

I just noticed there is a simple way of doing the problem

The given set of charges forms a dipole

U can use the equation of Field in axial line for a dipole