Physics Problems: electric forces and electric fields

 

1. Five styrofoam balls are suspended from insulating threads. Several experiments are performed on the balls and the following observations are made:

I. Ball A attracts B and repels C.

II. Ball D attracts B and has no effect on E.

III. A negatively charged rod attracts both A and E.

What are the charges, if any, on each ball?

          A  B C D  E           A  B C D  E      A  B C D  E      A  B C D  E

(a) +  – +   0   +        (b) + –   +   +   0   (c) +  –   +   0   0   (d) –  +  – 0   0

 

2. A conducting sphere has a net charge of -4.8 × 10-17 C. What is the approximate number of excess electrons on the sphere?     (a) 100    (b) 200    (c) 300    (d) 400    (e) 500

             

3. One mole of a substance contains 6.02 × 1023 protons and an equal number of electrons. If the protons could somehow be separated from the electrons and placed in very small, individual containers separated by 1.00 × 103 m, what would be the magnitude of the electrostatic force exerted by one box on the other?

(a) 8.7 × 108 N        (b) 9.5 × 109 N        (c) 2.2 × 1010 N      (d) 8.3 × 1013 N      (e) 1.6 × 1019 N

 

4. A -4.0-µC charge is located 0.30 m to the left of a +6.0-µC charge. What is the magnitude and    direction of the electrostatic force on the positive charge?

(a) 2.4 N, to the right       (b) 2.4 N, to the left    (c) 4.8 N, to the right (d) 4.8 N, to the left

 

5. Three charges are located along the x axis as shown in the drawing. The mass of the –1.2 µC is 4.0 × 10-9 kg. Determine the magnitude and direction of the acceleration of the –1.2 µC charge when it is allowed to move if the other two charges remain fixed.

(a) 2 × 105 m/s2, to the right        (b) 1 × 105 m/s2, to the left          (c) 7 × 104 m/s2, to the right

(d) 3 × 105 m/s2, to the left          (e) 4 × 106 m/s2, to the right

6. Each of two small non-conducting spheres is charged positively, the combined charge being 40 µC.  If each sphere is repelled from the other by a force having a magnitude of 2.0 N when the two spheres are 50 cm apart, determine the charge on the sphere having the smaller charge. 1.4 µC

 

7. A particle (charge = +40 µC) is located on the x axis at the point x = –20 cm, and a second particle (charge = –50 µC) is placed on the x axis at x = +30 cm.  What is the magnitude of the total electrostatic force on a third particle (charge = –4.0 µC) placed at the origin (x = 0)?  56 N

 

8. Three point charges, two positive and one negative, each having a magnitude of 20 µC are placed at the vertices of an equilateral triangle (30 cm on a side).  What is the magnitude of the electrostatic force on the negative charge? 69 N

 

9. Three point charges, two positive and one negative, each having a magnitude of 20 µC are placed at the vertices of an equilateral triangle (30 cm on a side).  What is the magnitude of the electrostatic force on one of the positive charges?  40 N

10. Which one of the following statements is true concerning the magnitude of the electric field at a point in space?

(a) It is a measure of the total charge on the object.

(b) It is a measure of the electric force on any charged object.

(c) It is a measure of the ratio of the charge on an object to its mass.

(d) It is a measure of the electric force per unit mass on a test charge.

(e) It is a measure of the electric force per unit charge on a test charge.

 

11. What is the magnitude of the electric field due to a 4.0 × 10-9 C charge at a point 0.020 m away?

(a) 1.8 × 103 N/C         (b) 9.0 × 104 N/C         (c) 1.0 × 105 N/C         (d) 3.6 × 106 N/C         (e) 7.2 × 107 N/C

 

12. A +2.0-nC point charge is placed at one corner of a square (1.5 m on a side), and a –3.0-nC charge is placed on a corner diagonally away from the first charge.  What is the magnitude of the electric field at either of the two unoccupied corners? 14 N/C

 

13.  A +15-nC point charge is placed on the x axis at x = 1.5 m, and a –20-nC charge is placed on the y axis at y = –2.0m.  What is the magnitude of the electric field at the origin?  75 N/C

 

14. A +20-nC point charge is placed on the x axis at x = 2.0 m, and a –25-nC point charge is placed on the y axis at y = –3.0 m.  What is the direction of the electric field at the origin?  209°

 

15. A charge Q is placed on the x axis at x = +4.0 m.  A second charge q is located at the origin.  If Q = +75 nC and q = –8.0 nC, what is the magnitude of the electric field on the y axis at y = +3.0 m? 23 N/C

 

16. A 40-µC charge is positioned on the x axis at x = 4.0 cm.  To produce a net electric field of zero at the origin where should a –60-µC charge be placed? 4.9 cm

 

17. A charge of 50 µC is placed on the y axis at y = 3.0 cm and a 77-µC charge is placed on the x axis at x = 4.0 cm.  If both charges are held fixed, what is the magnitude of the initial acceleration of an electron released from rest at the origin? 1.2 x 1020 m/s2

 

18. In the Diagram shown below, determine the resultant electrostatic force (magnitude and direction) on charge q1 due to the other charges shown.

 

19. In the diagram shown below, determine the resultant electric field (magnitude & direction) at point P due to the three charges shown. E = 7.2 x 107 n/c @ 95.5o

21. An edge-on view of two very large charged parallel plates is shown below.

If the total charge density on each plate is 20 uC/m2, determine the Electric Field between the plates. 2.26 x 106 n/c

If a positive 5 uC charge is placed next to the positive plate, determine the force on the charge. 11.3 n

Determine the velocity of the 5 uC charge when it reaches the negative plate. 23.7 m/s

The separation of the plates is 10 cm, and the mass of the charge is 4 grams.

22. Two charged thin spherical shells are shown below. Q1 = + 50 uC, Q2 = - 80 uC, R1 = 20 cm, R2 = 40 cm.

Determine the Resultant Electric Field at R =10 cm, R =30 cm, & R = 50 cm. (0, 5 x 106 n/c, -1.08 x 106 n/c)

Determine the Electric Potential at R =10 cm, R =30 cm, & R = 50 cm. (450,000 V, -300,000 V, -540,000 V)

 

23.  An edge on view of three very large (infinite) sheets of charge are shown below.  Sheet 1 has a surface charge density of +2 uC/m2 , Sheet 2 has a charge density of -4 uC/m2 , Sheet 3 has a charge density of +6 uC/m2.

 

Determine the resultant electric field due to all three sheets:  a) To the left of sheet 1. b) Between sheet 1 & 2. c) Between sheet 2 & 3. d) the right of sheet 2. ( -2.26 x 105 n/c, 0, -4.52 x 105 n/c, -2.26 x 105 n/c)

 

Determine the potential difference between point A in the exact middle between sheet 1 & 2, and point B in the exact middle between sheet 2 & 3. (4.52 x 104 Volts)