1. PHY 2049: Physics II We begin with a live clicker today.
Wileyplus homework should be fully operational.
Tea and Cookies: We meet on Tuesdays at 4:00PM for tea and cookies in room 2165.

2. quiz
The electric field at a distance of 1 m from an isolated point particle with a charge of 2×10−9 C is:
A. 1.8N/C B. 180N/C C. 18N/C D. 1800N/C E. none of these c

3. Quiz 2
An isolated charged point particle produces an electric field with magnitude E at a point 2m away from the charge. A point at which the field magnitude is 4E is:
A. 1m away from the particle
B. 0.5m away from the particle
C. 2m away from the particle
D. 4m away from the particle
E. 8m away from the particle

4. PHY 2049: Physics II Last week
Coulomb’s law, Electric Field and Gauss’ theorem
Today
Electric Potential Energy and Electric Potentials
Numerous cases

5. Potential Energy and Potential
Force => work => change in K=> change in Potential energy
ΔU = Uf – Ui = -W = - ΔK
Work done is path independent.
K+U = constant.
U = k q1 q2/r : interaction energy of two charges. Sign matters

6. PHY 2049: Physics II Electric Potential Also V = U/q = -W/q
Units of Joules/coulomb = volt
1 eV = e x 1V = 1.6 x J
Also
V = kq/r
Vf –Vi = -∫E.ds
In case of multiple charges, add as a number

7. Neg., lower ?
Pos., higher
Neg., higher
PHY 2049: Physics II
Conservation of energy tell us that Positive charge moves downhill (its kinetic energy increases) and negative charge moves uphill.
Can you tell the sign of the charge by looking at its behavior over a surface of potentials. Is the speed at the end bigger or smaller than in the beginning.

8. PHY 2049: Physics II Vf-Vi = -∫ k q/r2 dr Choose Vi = V (∞)=0
V(r) = kq/r

9. Uniformly charged disk
V = kpcosθ/r2
E = -∂V/∂s = -
Uniformly charged disk
V = ??

10. A B C
(24 - 6)

11. dq O A
(24 - 8)

12. PHY 2049: Physics II

13. . P r dq
(24 - 7)

14. (24 - 9)

15. ( )

16. S A B  V q S V
( )

17. ( )

18. ( ) A B V
V+dV

19. ( ) A B V
V+dV

20. ( ) x y O q1 q2 q3
r12
r23
r13

21. O x y  q1 Step 1 (24 - 16) x O r12 q1 q2  Step 2 Step 3 x y O r12

22. ( )
path A B
conductor

23. ( )

24. ( )

25. ( ) R