# Sample Exam 2 Phys 121 Number 6 Spring 2013 1. Identical 2.0

```Sample Exam 2 Phys 121 Number 6
Spring 2013
1. Identical 2.0-&micro;C charges are located on the vertices of a square with sides that are 2.0 m in length. Determine the electric potential
(relative to zero at infinity) at the center of the square.
A) 38 kV
B) 51 kV
C) 76 kV
D) 64 kV
E) 13 kV
3. A 15-cm radius conducting sphere is charged until the electric field just outside its surface is 120 V/m. The electric potential of the
sphere, relative to the potential far away, is:
A)
B)
C)
D)
E)
4.
0
6V
12 V
18 V
24 V
An electron is accelerated from rest through a potential difference of 2.5 kV. What is its final velocity?
A. 8x107 m/s
B. 3x107 m/s
C. 5x106 m/s
D. 8x105 m/s
E. 7x104 m/s
5. The potential energy at x = 8 m is -2000 V and at x = 2 m is 400 V. What is the magnitude and the direction of the electric field?
A)
B)
C)
D)
E)
100 V/m directed parallel to the +x-axis
250 V/m directed parallel to the - x-axis
400 V/m directed parallel to the + x-axis
400 V/m directed parallel to the -x – axis
600 V/m directed parallel to the +x-axis
4. A hollow metal sphere is charged to a potential V. The potential at its center is:
A. V
B) 0
C) -V
D) 2V
E) -2 V
6. In the circuit shown capacitor C1 = 2nF is first charged by closing of switch S, and connecting it to
battery of ∆V = 42 V. Switch S1 is then opened, and charged capacitor is connected to the uncharged
capacitor C2 by closing switch S2. If the final potential across C2 is 15 V, what is the capacitance of
capacitor C2?
A)
B)
C)
D)
E)
1 . 6 nF
2 .0 nF
3.6 nF
6.0 nF
4.2 nF
7. What maximum potential difference (before it breaks down) can be applied to an air filled parallel-plate capacitor C = 2 nF if the
surface area is 8x10 -4 m2? (dielectric strength of air is E = 3x106 V/m)
A)
B)
C)
D)
E)
2V
5V
7V
11V
15 V
8. Find the distance between two parallel, circular, metal plates of radius 10 cm that constitutes a capacitor with C= 40 pF.
A)
B)
C)
D)
E)
2.2mm apart.
7mm apart
0.7m apart.
22mm apart.
70mm apart
9. Determine the energy stored by C4 when C1 = 20 &micro;F, C2 = 10 &micro;F, C3 = 14 &micro;F, C4 = 30 &micro;F, and V0 = 45 V.
A)
B)
C)
D)
E)
3.8 mJ
2.7 mJ
3.2 mJ
2.2 mJ
8.1 mJ
10. A 10-m long aluminum wire with a radius of 0.4 mm carries a current of 5 A. If resistivity of aluminum is 2.75x10-8 Ωm. what is the
potential difference across this wire?
A)
B)
C)
D)
E)
2.7 V
8.6 V
12.5 V
18.2 V
23.4 V
11. A 1.5-V potential difference is maintained across a 1.5-m length of tungsten wire (resistivity =5.25x10-8 Ωm) that has a cross-sectional
area of 0.6 mm2. How much power is dissipated in the wire?
A) 17 W
B) 15 W
C) 12 W
D) 8 W
E) 4 W
12. What is the current in the 15-Ω resistor when ε = 9.0 V?
20 Ω
+
15 Ω
E
30 Ω
–
A)
B)
C)
D)
E)
0.20 A
0.30 A
0.10 A
0.26 A
0.60 A
13. The current in a wire is I = 15x10-3A. How many electrons will pass a point in this wire in 4 min? (e = 1.6x1 0-19C)
A) 8.1014
B) 5.4.1016
C) 1.22.1015
D) 2.25.1019
E) None
14. A 0.26 V potential difference is applied to a 2 m long copper wire of cross –section of 2.25 mm2. The resistivity of copper is
1.68x10-8 Ωm and the number of charge carriers per unit volume is 8.48x1028 m-3 . What is electron drift velocity?
A) 5.7x10-4 m/s
B) 2.3x10-1 m/s
C) 1.5x10-4 m/s
D) 5.7x10-2 m/s
E) 1.7x10-6 m/s
15.
A conductor of radius r, length and resistivity ρ has resistance R. It is melted down and formed into a new conductor, also
cylindrical, with one third the length of the original conductor. The resistance of the new conductor is
A)
B)
R
C) R
D) 3R
E) 9R
16. Light bulb A is rated at 60 W and light bulb B is rated at 100 W. Both are designed to operate at 110 V. Which statement is correct?
A) The 60 W bulb has a greater resistance and greater current than the 100 W bulb.
B) The 60 W bulb has a greater resistance and smaller current than the 100 W bulb.
C) The 60 W bulb has a smaller resistance and smaller current than the 100 W bulb.
D) The 60 W bulb has a smaller resistance and greater current than the 100 W bulb.
E) We need to know the resistivities of the filaments to answer this question.
17.
What is the potential difference VB – VA when I = 0.50 A in the circuit segment shown below?
10 Ω
16 Ω
+
–
15 V
A)
B)
C)
D)
E)
+28 V
+2.0 V
–28 V
–2.0 V
+18 V
I
B
A
For circuit shown
18. Find the equivalent resistance of the circuit is
A) 5 Ω
B) 10 Ω
C) 15 Ω
D) 20 Ω
E) 26 Ω
19. Find the potential difference across resistance R3.
A) 2.8 V
B) 5.5 V
C) 7.1 V
D) 8.9 V
E) 10 V
Consider the circuit below:
20. What is the magnitude of the current in the 20-Ω resistor?
A)
B)
C)
D)
E)
0.75 A
0.00 A
0.25 A
0.50 A
1.00 A
21. What is the current through 10 V battery?
A) 0.21 A
B) 0 74 A
C) 0.11 A
D) 0.0 A
E) 0.55 A
```