2. PHY 2049: Physics II Coulomb’s law:
Two kinds of charges, positive and negative, unlike attract, like repel.
Electrons and Protons:
q = ± x C
Current I = dq/dt Amp. = 1 C/s
Add forces as vectors

3. 3,1,2
PHY 2049: Physics II
Balls are touched and then separated. Rank them by
Charge left
Magnitude of Force before
After
Charge transferred

4. PHY 2049: Physics II
A rule
Try to calculate the force magnitude by ignoring the signs of charges. Then assign the direction by looking at the signs.
Never do both (using the charge signs in the calculation of the force and then assign the direction).

5. Phy 2049: Physics II trial run
[-0.344N, N], º
Phy 2049: Physics II trial run
In Fig. at right, the particles have charges q1 = -q2 = 300 nC and q3 = -q4 = 200 nC, and distance a = 4.0 cm.
What is the direction of the force on particle 4?
A B.
C D.

6. TALP: Take a look Problem
PHY 2049: Physics II
Force on the center charge = 6kq2/d2
Direction: -x, 180º, d

7. PHY 2049: Physics II q1 = q4 = Q; q2 = q3 = q
what is Q/q so that the force on 1 is zero
All charges same sign. There is no solution.
Q and q different sign. There is a possible solution.
Is the answer the same if the force on 3 is to be zero

8. PHY 2049: Physics II What is the force on the central chlorine ion?
Suppose that we put in an electron that sits on a cesium site and neutralizes it, which way does the Chlorine move?

9. PHY 2049: Physics II Electric Field Force F = qE E = k ∑ rˆ qi/ri2
environment
Electric Field
Force F = qE
E = k ∑ rˆ qi/ri2
Test charge

10. PHY 2049: Physics II
q1 = 2Q
q2 = - 2Q
q3 = -4Q
E at origin

12. Electric field lines denote direction
Their density represents magnitude
They do not cross

13.     
Physics II

14. PHY 2049: Physics II

15. PHY 2049: Physics II Induction and charge transfer on contact
Forces summed as vectors
Electric fields

16. PHY 2049: Physics II

17. Potentials add like numbers
Physics II