WORK, CAPACITANCE AND DIELECTRICS

1. An electron in a TV picture tube is accelerated through a potential difference of 10 kV

before it hits the screen What is the kinetic energy of the electron in electron volts? (1 eV

= 1.6 10-19 J)

a. 1.0 104 eV b. 1.6 10-15 eV c. 1.6 10-22 eV d. 6.25 1022 eV

2. Three capacitors of 1.0, 1.5, and 2.0 microFarads are connected in series. Find the

combined capacitance.

a. 4.5 microFarads b. 4.0 microFarads c. 2.17 microFarads d. 0.46 microFarads

3. If three 4.0 F capacitors are connected in parallel, what is the combined capacitance? a. 12 microFarads b. 0.75 microFarads c. 8.0 microFarads d. 0.46 microFarads

4. A 10.0 microFarad capacitor is attached to a 20 V power supply. How much energy is

stored in the capacitor?

a. 2 10-3 J b. 1.2 10-3 J c. 2 10-4 J d. 5.2 10-4 J

5. The unit of capacitance, the farad, is dimensionally equivalent to which of the following?

a. volt/coulomb b. volt coulomb c. joule/volt d. coulomb/volt

6. Two capacitors with capacitances of 1.0 and 0.5 microFarads, respectively, are connected

in series. The system is connected to a 100 V battery. What charge accumulates on the 1.0

microFarad capacitor?

a. 150 microCoul b. 100 microCoul c. 50 microCoul d. 33 microCoul

7. If C1 = 15F, C2 = 10 F, C3 = 20 F, and Vo = 18 V, determine the energy stored by C2

a. 0.72 mJ

b. 0.32 mJ

c. 0.50 mJ

d. 0.18 mJ

8. If C = 36 F, determine the equivalent capacitance for the combination shown.

a. 36 F

b. 32 F

c. 28 F

d. 24 F

9. A parallel-plate capacitor is constructed by filling the space between two square plates with blocks of three dielectric materials, as in Figure. You may asume that l >>d. (a) Find an expression

for the capacitance of the device in terms of the plate area A and d, k1, k2, and k3. (b) Calculate the capacitance using the values A= 1 cm2, d = 2 mm, k1 = 4.90, k2= 5.60, and k3= 2.1

10. a) Find the work to move a charge Q=-20 C from the origin to (4,0,0) m in the field:

b) Now move the charge from (4,0,0 )to (4,2,0) and determine the work done.

C

C 2C

2C

V0+-

C1

C2 C3