Physics 202 MWF 10:20 Spring 2004 (Ford)

Exam I Chapts. 18 and 19 in Cutnell and Johnson 6th ed.

Multiple choice questions. Circle the correct answer. No work need be shown and no partial credit will be given.

(3 pts) 1. A thin hollow spherical shell has radius R = 0.60 m. At a point inside the shell, at a distance of 0.30 m from the center of the shell, the electric potential is +300 V. What is the electric potential at the surface of the shell, 0.60 m from the center?

(a) zero
(b) +150 V
(c) +300 V<--------
(d) +600 V


(3 pts) 2. Two large parallel conducting plates are separated by 0.0040 m. The plates have equal and opposite charge. The electric field midway between the two plates is 900 N/C. What is the potential difference between the two plates?

(a) zero
(b) 1.8 V
(c) 3.6 V<--------
(d) 7.2 V
(e) 250 V


(3 pts) 3. A negative point charge moves from point A to point B. The only force on the charge is the electric force. The kinetic energy of the charge at point A is 3.0 J and at point B it is 7.0 J. Which of the following is the correct statement about the relation between the electric potentials at A and B:

(a) V_A < V_B<--------
(b) V_A = V_B
(c) V_A > V_B


(3 pts) 4. A parallel-plate capacitor with air between the plates is connected to a 20.0-V battery until it is fully charged. It is then disconnected from the battery without any charge leaving the plates. After it is disconnected from the battery, a slab of dielectric with dielectric constant = 4.0 is inserted between the plates. When the dielectric fills the space between the plates, what is the potential difference between the plates of the capacitor?

(a) 20.0 V
(b) zero
(c) 80.0 V
(d) 5.0 V<--------


(3 pts) 5. A negative point charge is at point P. There is an electric field at P and this field exerts a force on the charge that has direction due west. What is the direction of the electric field?

(a) east<--------
(b) west
(c) north
(d) south


(3 pts) 6. There is a uniform electric field that is directed upward. Point B is 2.0 m directly below point A. Which of the following is the correct statement about the relation between the electric potentials at A and B:

(a) V_A < V_B<--------
(b) V_A = V_B
(c) V_A > V_B



Show all your work. Partial credit will be given if earned. Write your answers in the blanks provided.


(22 pts) 7. Point charge q₁ = -6.0 × 10^-6 C is at the origin and point charge q₂ = +4.0 × 10^-6 C is on the x-axis at x = 0.4 m. Point P is on the y-axis at y = +0.3 m. What are the x- and y-components of the total electric field at point P due to q₁ and q₂? You must indicate whether each component is positive or negative.



Ans. Ex = ___-1.15 × 10⁵ N/C_____

E_y = __-5.13 × 10⁵ N/C____


(20 pts) 8. A solid conducting sphere with radius R₁ is at the center of a hollow conducting sphere. The hollow sphere has inner radius R₂ and outer radius R₃. There is a net charge +2q on the solid sphere and a net charge of -6q on the hollow sphere.



a) In terms of k, q and the distance r from the center of the spheres, what is the electric field in each of the following regions:

(i) r < R₁ (within the solid sphere)

Ans. ____0____

(ii) R₁ < r < R₂ (in the air space between the two spheres)

Ans. ____2kq/r², outward_______

(iii) r > R₃ (outside the hollow sphere)

Ans. ___4kq/r², inward_

b) In terms of q, what is the total charge on the outer (exterior) surface of the hollow sphere?

Ans. _____-4q____


(20 pts) 9. A small particle with a charge of +8.0 × 10^-6 C is released from rest at point A and moves toward point B. The only force on the particle is the electric force. When the particle arrives at point B it's kinetic energy is 2.0 × 10^-3 J. If the electric potential at point B is 400 V, what is the electric potential at point A?

Ans. ____650 V____


(20 pts) 10. Point charges q₁ = +2.0 × 10^-6 C and q₂ = -2.0 × 10^-6 C are placed at adjacent corners of a square that has length 0.030 m. Point A is at the center of the square and point B is at the empty corner closest to q₂. A point charge q₃ = -5.0 × 10^-6 C moves from point A to point B. How much work is done by the electric force as q₃ moves from A to B? Is this work positive or negative?



Ans. W_AB = ____-0.875 J____

positive or negative? ____negative_______