Download Physics 2401 Summer 2, 2012 Exam 1

Physics 2401 Summer 2, 2012
Exam 1
e = 1.60x10-19 C, m(electron) = 9.11x10-31 kg, ε0 = 8.845x10-12 C2/Nm2,
-9
ke = 9.0x109 Nm2/C2, m(proton) = 1.67x10-27 kg. n = nano = 10 , µ = micro = 10-6, m = milli = 10-3
Put your answers on the orange scantron which you brought. Write down and bubble in
(correctly) your R# before you do anything else. All questions are weighted equally.
1. Two point charges which are a distance d apart exert a force F on each other. If their
separation is increased to 3d, the force becomes
a) 9F b) 3F c) F d) F/3 e) F/9
2. We rub two objects together and they acquire charges. Which of the following is true?
a) protons move to the object which becomes positively charged
b) electrons move to the object which becomes negatively charged
c) Both a) and b)
d) the negatively charged object has a greater magnitude of charge than the positively charged
object
3. Two positive 2.0 microCoulomb charges are placed on the y axis at y=-0.20 m and y=0.20 m.
What is the electric field at x=0.30 m on the x axis, in N/C?
5
a) 1.54x106, +x direction b) 1.54x106, +y direction c) 2.30x10 , +x direction
d) 2.30x105, - x direction
4. A 2.0 gram particle with a charge of –2.5 microCoulombs is placed in a 120,000 N/C electric
field which points in the +y direction. Its acceleration when released is, in m/s2,
a) 50, +y direction b) 50, -y direction c) 150, +y direction d) 150, -y direction
5. A hollow metallic sphere is placed in an electric field that points upwards. Which statement
about the electric field in the sphere’s interior is correct, iof it has reached electrostatic
equilibrium?
a) The field is upwards
b) The field is downwards
c) The field is radially outwards from the sphere’s center
d) The field is zero
6. Two conducting plates of area 1.8 square meters are placed parallel to each other, separated by
0.80 cm. They carry equal and opposite charges with a magnitude of 25 microCoulombs. The
electric field between them is, in N/C,
a) 1.57x106 b) 0.0031 c) 2.82x106
d) 112,000
e) 0.0056
7. A +6.0 microCoulomb charge is at x=0 and a –2.0 microCoulomb charge is at x=0.50 m on the
x axis. Where, in m, is the electric field zero?
a) 0.32 m b) 1.28 m c) 4.72 m
d) 1.18 m
e) 0.75 m
8. A + 3.0 microCoulomb has 10 field lines attached to it in an electric field diagram. A nearby
–18.0 microCoulomb charge will have which of the following?
a) 18 lines pointing in
b) 6 lines pointing in
c) 60 lines pointing in
d) 18 lines pointing out
e) 60 lines pointing out
9. A circular ring has a uniform charge per unit length λ = 50 microCoulombs/meter and a radius
of 2.0 cm. The electric field on the axis a distance of 25 m away is approximately what non-zero
value, in N/C?
a) 1800 b) 44 c) 230 d) 90 e) 720
10. An proton moves a distance of 3.5 cm in the direction of a 10,000 N/C electric field. If it
begins at rest, its final speed is what, in m/s?
a) 2.6x105 b) 1.1x107 c) 1.6x107 d) 2.5x106 e) 1.8x105
11. A cube with sides a has a point charge Q at its center. What is the electric flux through ONE
of the faces of the cube?
a) Q/ε0
b) 6Q/ε0
c) 4Q/ε0
d) Q/4ε0
d) Q/6ε0
12. We have three point charges, q1, q2, and q3 all at different points in space. A closed surface S
encloses q1 and q2, but not q3. The net flux through S is
a) q3/ε0 b) (q1+q2)/ε0 c) (q1+q2-q3)/ε0 d) (q1+q2+q3)/ε0
e) 0
13. A conducting sphere with charge 3Q is surrounded by a conducting, concentric shell with a
net charge of –Q. The charge residing on the inner surface of the conducting shell is
a) –Q b) 0 c) 3Q
d) –2Q
e) –3Q
14. The electric field magnitude a distance r away from the center of the center sphere in
problem 13, where r is located outside of the shell, is
a) ke
€
Q
r
2
b) 2 ke
Q
r
2
c) -2 ke
Q
r
2
d) 0
e) 3 ke
Q
r2
15. The electric potential inside a charged spherical conductor in electrostatic equilibrium is
a) constant
€ and equal€to the value at its surface
€
b) zero everywhere inside
c) increases from the surface value to a multiple of it at the center
d) drops linearly to zero as the center is approached
16. A +20 microCoulomb charge is placed at the origin, while a -35 microCoulomb charge is
placed on the x axis at x=5.0 m. For what value of x on the x axis will the electric potential be
zero?
a) -2.2 b) -6.7 c) 0.78 d) 2.8 e) 1.8
17. The electric potential in some region of space is given by V (x) = 3.5x 2 − 1.6xy + 4.4 y 2 . The x
component of the electric field is
a) 3.5x –1.6y b) +1.6y -4.4y2
c) -1.17x3+0.8x2y-4.4xy2
d) -7.0x+1.6y
€
18. When a charge with q = 2e moves under the influence of the electric force and an external
force through a potential difference of -80 V, its kinetic energy increases by 200 eV. The work
done by the external force is, in eV,
a) 200 b) -160 c) 160 d) 40 e) -60
20. Three equal charges Q = 30 microCoulombs are held at the corners of an equilateral triangle
with sides 0.050 m. If one of the charges, which has a mass of 0.0020 kg, is released, what is its
speed in m/s when it has flown away to a great distance from the other charges?
a) 570
b) 320 c) 32,000 d) 330,000
e) 3x108