Question 1

A pair of parallel plates,forming a capacitor,are connected to a battery.While the capacitor is still connected to the battery maintaining a constant voltage,the plates are pulled apart to triple their original distance.What is the ratio of the final energy stored to the original energy stored?

Accepted Answer

A)  3 
B)  1 
C)  1/3 
D)  1/9 
E)  ​9

Question 2

If two parallel,conducting plates have equal positive charge,the electric field lines will:

Accepted Answer

A)  leave one plate and go straight to the other plate. 
B)  leave both plates and go to infinity. 
C)  enter both plates from infinity. 
D)  none of the above.

Question 3

If an electron is accelerated from rest through a potential difference of 1,000 V,find its approximate velocity at the end of this process.(e = 1.6 × 10−19 C;me = 9.1 × 10−31 kg)

Accepted Answer

A)  2.4 × 107 m/s 
B)  18.8 × 107 m/s 
C)  1.9 × 107 m/s 
D)  3.5 × 107 m/s 
E)  ​12.4 × 107 m/s

Question 4

Two equal positive charges are separated by d.Then one of the charges is replaced by a negative charge of the same magnitude.Take the potential at infinity to be zero.In which situation is the potential higher midway between the charges;is this value of potential zero?

Accepted Answer

A)  the first situation;yes 
B)  the first situation;no 
C)  the second situation;yes 
D)  the second situation;no

Question 5

Two parallel-plate capacitors have the same plate area,and the gap between the plates is filled with a dielectric with a dielectric constant equal to 8.The gap in capacitor A is one half that in Capacitor B.What is the ratio of the capacitance of A to B?

Accepted Answer

A)  4 
B)  1 
C)  1/4 
D)  8 
E)  ​The ratio is not given.

Question 6

What is the equivalent capacitance of the combination shown?

Accepted Answer

A)  24 µF 
B)  100 µF 
C)  12 µF 
D)  4.6 µF

Question 7

There is a hollow,conducting,uncharged sphere with a negative charge inside the sphere.Consider the electrical potential at the inner and outer surfaces of the sphere.Which of the following is true?

Accepted Answer

A)  The potential on the inner surface is greater. 
B)  The potential on the outer surface is greater. 
C)  The potentials on both surfaces are zero. 
D)  The potentials on both surfaces are equal but not zero.

Question 8

Two capacitors with capacitances of 1.0 μF and 0.35 μF,respectively,are connected in parallel.The system is connected to a 40-V battery.What electrical potential energy is stored in the 1.0-μF capacitor?

Accepted Answer

A)  0.1 × 10−3 J 
B)  0.3 × 10−3 J 
C)  0.8 × 10−3 J 
D)  1.1 × 10−3 J 
E)  ​2.8 × 10−3 J

Question 9

A free electron is in an electric field.With respect to the field,it experiences a force acting:

Accepted Answer

A)  parallel. 
B)  anti-parallel (opposite in direction). 
C)  perpendicular. 
D)  along a constant potential line.

Question 10

If the distance between two negative point charges is increased by a factor of three,the resultant potential energy is what factor times the initial potential energy?

Accepted Answer

A)  3.0 
B)  9.0 
C)  1/3 
D)  1/9

Question 11

If C1 = 30 µF,C2 = 25 µF,C3 = 15 µF,and ΔV0 = 22 V,determine the energy stored by C2.

Accepted Answer

A)  2.0 mJ 
B)  1.4 mJ 
C)  1.7 mJ 
D)  1.1 mJ 
E)  ​5.4 mJ

Question 12

A 4-μF capacitor is attached to a 10-V power supply.How much energy is stored in the capacitor?

Accepted Answer

A)  0.40 × 10−3 J 
B)  4 × 10−3 J 
C)  1.60 × 10−4 J 
D)  4 × 10−4 J 
E)  ​1.50 × 10−3 J

Question 13

Two protons,each of charge 2.2 × 10-19 C,are 4.6 × 10-5 m apart.What is the change in potential energy if they are brought 2.3 × 10-5 m closer together? (ke = 8.99 × 109 N·m2/C2)

Accepted Answer

A)  0.95 × 10−23 J 
B)  1.35 × 10−19 J 
C)  1.89 × 10−16 J 
D)  0.12 × 10−14 J 
E)  ​0.23 × 10−19 J

Question 14

Two capacitors with capacitances of 1.25 and 3.75 μF,respectively,are connected in parallel.The system is connected to a 45-V battery.What charge accumulates on the 1.25-μF capacitor?

Accepted Answer

A)  4.69 μC 
B)  56.25 μC 
C)  0.10 μC 
D)  9.60 μC 
E)  0.33​ μC

Question 15

A 20-μF capacitor is attached across a 1000-V power supply.What is the net charge on the capacitor?

Accepted Answer

A)  10 mC 
B)  20 mC 
C)  40 mC 
D)  none of the above

Question 16

A parallel-plate capacitor with plate area A and plate separation d has a capacitance of 3 
With the gap between the plates unfilled.The gap is then filled with two dielectric materials,one with dielectric constant 3 and the other one with dielectric constant 6.Each slab of dielectric has area A and thickness d/2,the layering of the dielectrics resulting in the gap being completely filled.Which of the following combinations of capacitors will have the same capacitance as the newly filled parallel-plate one?

Accepted Answer

A)  a 9-
 capacitor and a 18-
 capacitor in parallel 
B)  a 9-
 capacitor and a 18-
 capacitor in series 
C)  a 18-
 capacitor and a 36-
 capacitor in parallel 
D)  a 18-
 capacitor and a 36-
 capacitor in series 
E)  ​a 9-
 capacitor and a 36-
 capacitor in parallel

Question 17

A capacitor is made by taking two sheets of aluminum foil,each 0.022 mm thick and placing between them a sheet of paper which comes from a ream of 520 sheets,the ream being 5.3 cm thick with sheets measuring 216 mm by 279 mm (the usual 8 1/2 by 11).What is the capacitance of the capacitor made this way if the dielectric constant of the paper is 3.7? (ε0 = 8.85 × 10-12 C2/N × m2)

Accepted Answer

A)  33 nF 
B)  45 nF 
C)  19 nF 
D)  1.5 nF 
E)  ​5 nF

Question 18

If the distance between two isolated parallel plates that are oppositely charged is doubled,the electric field between the plates is essentially unchanged.However,the:

Accepted Answer

A)  potential difference between the plates will double. 
B)  charge on each plate will double. 
C)  force on a charged particle halfway between the plates will get twice as small. 
D)  force on a charged particle halfway between the plates will get four times as small.

Question 19

A solid conducting sphere of 9 cm radius has a net charge of 17 nC.If the potential at infinity is taken as zero,what is the potential at the center of the sphere?

Accepted Answer

A)  2.5 μV 
B)  13.8 μV 
C)  1.7 × 103 V 
D)  >1.7 × 104 V 
E)  ​9.3 μV

Question 20

Three capacitors of 0.6,1.6,and 2.6 μF are connected in series.Find the combined capacitance.

Accepted Answer

A)  2.68 μF 
B)  4.80 μF 
C)  7.00 μF 
D)  0.37 μF 
E)  0.85​ μF

Exam 16: Electrical Energy and Capacitance