Sample Problems 2

Practice problems for exam 2. Physics 2150.

A 16-nC charge is distributed uniformly along the x axis from x = 0 to x = 4 m. Which of the following integrals

is correct for the magnitude (in N/C) of the electric field at x = +10 m on the x axis?

a.

b.

c.

d.

e. none of these

ANS: A PTS: 2 DIF: Average

A uniform linear charge of 3.0 nC/m is distributed along the y axis from y = 3 m to y = 2m. Which of the following integrals is correct for the magnitude of the electric field at y = 4 m on the y axis?

a.

b.

c.

d.

e. none of these

ANS: A PTS: 2 DIF: Average

Charge Q is distributed uniformly along a semicircle of radius a. Which formula below gives the correct

magnitude of the electric field at the center of the circle?

a.

. b.

.

c.

. d.

. e.

.

ANS: D PTS: 2 DIF: Average

Two infinite, uniformly charged, flat surfaces are mutually perpendicular. One of the sheets has a charge density

of +60 pC/m2, and the other carries a charge density of 80 pC/m2. What is the magnitude of the electric field at any point not on either surface?

a. 1.1 N/C b. 5.6 N/C c. 7.9 N/C d. 3.8 N/C e. 4.0 N/C

ANS: B PTS: 2 DIF: Average

A long cylinder (radius = 3.0 cm) is filled with a nonconducting material which carries a uniform charge density

of 1.3 C/m3. Determine the electric flux through a spherical surface (radius = 2.0 cm) which has a point on the axis of the cylinder as its center.

a. 5.7 N m2/C b. 4.9 N m2/C c. 6.4 N m2/C d. 7.2 N m2/C e. 15 N m2/C


A long nonconducting cylinder (radius = 6.0 mm) has a nonuniform volume charge density given by r2, where = 6.2 mC/m5 and r is the distance from the axis of the cylinder. What is the magnitude of the electric field at a point 2.0 mm from the axis?

a. 1.4 N/C b. 1.6 N/C c. 1.8 N/C d. 2.0 N/C e. 5.4 N/C

ANS: A PTS: 3 DIF: Challenging

A 5.0-nC point charge is embedded at the center of a nonconducting sphere (radius = 2.0 cm) which has a charge

of 8.0 nC distributed uniformly throughout its volume. What is the magnitude of the electric field at a point that is 1.0 cm from the center of the sphere?

a. 1.8 105 N/C b. 9.0 104 N/C c. 3.6 105 N/C d. 2.7 105 N/C e. 7.2 105 N/C

ANS: C PTS: 2 DIF: Average

A particle (charge = +2.0 mC) moving in a region where only electric forces act on it has a kinetic energy of 5.0

J at point A. The particle subsequently passes through point B which has an electric potential of +1.5 kV

relative to point A. Determine the kinetic energy of the particle as it moves through point B.

a. 3.0 J b. 2.0 J c. 5.0 J d. 8.0 J e. 10.0 J


Point charges q and Q are positioned as shown. If q = +2.0 nC, Q = 2.0 nC, a = 3.0 m, and b = 4.0 m, what is

the electric potential difference, VA VB?

a. 8.4 V b. 6.0 V c. 7.2 V d. 4.8 V e. 0 V


Four identical point charges (+4.0 C) are placed at the corners of a square which has 20-cm sides. How much work is required to assemble this charge arrangement starting with each of the charges a very large

distance from any of the other charges?

a. +2.9 J b. +3.9 J

c. +2.2 J d. +4.3 J e. +1.9 J

ANS: B PTS: 3 DIF: Challenging

A charge per unit length given by (x) = bx, where b = 12 nC/m2, is distributed along the x axis from x = +9.0 cm to x = +16 cm. If the electric potential at infinity is taken to be zero, what is the electric potential at the

point P on the y axis at y = 12 cm?

a. 5.4 V b. 7.2 V c. 9.0 V d. 9.9 V e. 16 V


A charge of 10 nC is distributed uniformly along the x axis from x = 2 m to x = +3 m. Which of the following integrals is correct for the electric potential (relative to zero at infinity) at the point x = +5 m on the x

axis?

a.

b.

c.

d.

e.


2.Determine the equivalent capacitance of the combination shown when C = 15 mF.

a. 20 mF b. 16 mF c. 12 mF d. 24 mF e. 75 mF


3. Determine the equivalent capacitance of the combination shown when C = 12 nF.

a. 34 nF b. 17 nF c. 51 nF d. 68 nF e. 21 nF


Determine the energy stored in C2 when C1 = 15 F, C2 = 10 F, C3 = 20 F, and V0 = 18 V.

a. 0.72 mJ b. 0.32 mJ c. 0.50 mJ d. 0.18 mJ e. 1.60 mJ

ANS: D PTS: 3 DIF: Challenging

A 30-F capacitor is charged to 40 V and then connected across an initially uncharged 20-F capacitor. What is the final potential difference across the 30-F capacitor? a. 15 V b. 24 V

c. 18 V d. 21 V e. 40 V


33. A capacitor of unknown capacitance C is charged to 100 V and then connected across an initially

uncharged 60-F capacitor. If the final potential difference across the 60-F capacitor is 40 V, determine C.

a. 49 F b. 32 F c. 40 F d. 90 F e. 16 F


Addition of a metal slab of thickness a between the plates of a parallel plate capacitor of plate separation d is

equivalent to introducing a dielectric with dielectric constant between the plates. The value of is a.

. b. d. c. d a. d.

. e.

.


A 4.0- resistor has a current of 3.0 A in it for 5.0 min. How many electrons pass through the resistor during this time interval?

a. 7.5 1021 b. 5.6 1021 c. 6.6 1021 d. 8.4 1021 e. 2.1 1021


8. If 5.0 1021 electrons pass through a 20- resistor in 10 min, what is the potential difference across the resistor?

a. 21 V b. 32 V c. 27 V d. 37 V e. 54 V


A conductor of radius r, length and resistivity has resistance R. What is the new resistance if it is stretched to 4 times its original length?

a.

R b.

R c. R d. 4R e. 16R

ANS: E PTS: 2 DIF: Average

A small bulb is rated at 7.50 W when operated at 125 V. The tungsten filament has a temperature coefficient of

resistivity = 4.50 103 / C. When the filament is hot and glowing, its temperature is seven times room temperature (20 C). What is the resistance of the filament (in ohms) at room temperature? a. 234 b. 1 350 c. 2 080 d. 4 530 e. 5 630


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