1. General Physics II, Lec 4, By/ T.A. Eleyan 1 Lecture 4 Discussion

2. General Physics II, Lec 4, By/ T.A. Eleyan 2 [1] In figure, two equal positive charges q=2x10 -6 C interact with a third charge Q=4x10 -6 C. Find the magnitude and direction of the resultant force on Q.

3. General Physics II, Lec 4, By/ T.A. Eleyan 3 [2] A charge Q is fixed at each of two opposite corners of a square as shown in figure. A charge q is placed at each of the other two corners. If the resultant electrical force on Q is Zero, how are Q and q related.

4. General Physics II, Lec 4, By/ T.A. Eleyan 4 [3] Two fixed charges, 1µC and -3µC are separated by 10cm as shown in figure (a) where may a third charge be located so that no force acts on it? (b) is the equilibrium stable or unstable for the third charge?

5. General Physics II, Lec 4, By/ T.A. Eleyan 5

6. 6 [4] Find the electric field at point p in figure due to the charges shown. Solution:

7. General Physics II, Lec 4, By/ T.A. Eleyan 7 [5] A charged cord ball of mass 1g is suspended on a light string in the presence of a uniform electric field as in figure. When E=(3i+5j) *10 5 N/C, the ball is in equilibrium at Θ=37 o. Find (a) the charge on the ball and (b) the tension in the string. Substitute T from equation (1) into equation (2) Substitute by q into equation (1) to find T=5.44*10 -3 N

8. General Physics II, Lec 4, By/ T.A. Eleyan 8 [6] A 1.3µC charge is located on the x-axis at x=-0.5m, 3.2µC charge is located on the x-axis at x=1.5m, and 2.5µC charge is located at the origin. Find the net force on the 2.5µC charge

9. General Physics II, Lec 4, By/ T.A. Eleyan 9 [7] Two free point charges +q and +4q are a distance 1cm apart. A third charge is so placed that the entire system is in equilibrium. Find the location, magnitude and sign of the third charge. Is the equilibrium stable?

10. General Physics II, Lec 4, By/ T.A. Eleyan 10 [8] Two protons in a molecule are separated by a distance of 3.8*10 -10 m. Find the electrostatic force exerted by one proton on the other. [9] The electric force on a point charge of 4.0mC at some point is 6.9*10 - 4 N in the positive x direction. What is the value of the electric field at that point?

11. General Physics II, Lec 4, By/ T.A. Eleyan 11 [10] Two point charges are a distance d apart. Find E points to the left P. Assume q1=+1.0*10 -6 C, q2=+3.0*10 -6 C, and d=10cm

12. General Physics II, Lec 4, By/ T.A. Eleyan 12 [11] Calculate E (direction and magnitude) at point P in Figure.

13. General Physics II, Lec 4, By/ T.A. Eleyan 13 [12] A uniform electric field exists in a region between two oppositely charged plates. An electron is released from rest at the surface of the negatively charged plate and strikes the surface of the opposite plate, 2.0cm away, in a time 1.5*10 -8 s. (a) What is the speed of the electron as it strikes the second plate? (b) What is the magnitude of the electric field.

14. General Physics II, Lec 4, By/ T.A. Eleyan 14 [13] Three charges are placed on corners of an equilateral triangle as shown in Figure 1. An electron is placed at the center of the triangle. What is the magnitude of the net force on the electron?

15. General Physics II, Lec 4, By/ T.A. Eleyan 15 [14] A uniform electric field exists in the region between two oppositely charged plane parallel plates. An electron is released from rest at the surface of the negatively charged plate and strikes the surface of the opposite plate 2x10 -8 s later. If the magnitude of the electric field is 4x10 3 N/C, what is the separation between the plates?