PHY2054 - Final - Fall 1997 - Selman Hershfield
- As shown in Fig. 1(a) and (b),
when a rod is moved closer to an electroscope, the leaves of the
electroscope move further apart.
Which of the following is true?
- The electroscope must be charged, i.e, the net charge is not zero.
- The rod can not be overall neutral and metallic.
- The electroscope can have an overall positive charge, if the rod is a positively charged insulator.
- The electroscope can have an overall positive charge, if the rod is a negatively charged insulator.
- None of the other answers is correct.
- Four charges are arranged on a rectangle as shown in Fig. 2.
What is the magnitude of the force on Q3 ?
- 1340 N
- 1490 N
- 1560 N
- 1730 N
- 1900 N
- In the above problem, what is the direction of the force on Q3 ?
- 112 degrees
- 145 degrees
- 176 degrees
- 184 degrees
- 248 degrees
- The large parallel planes shown in Fig. 3 have charge per unit
area of sigma 1 = -8x10-9 C/m2 ,
sigma 2 = -8x10-9 C/m2 , and sigma 3 = 2x10-9 C/m2 .
What is the electric field at point P2? Use the convention
that positive is in the +x direction, and negative is in the
-x direction.
- -1017 N/C
- -791 N/C
- -113 N/C
- +113 N/C
- +1017 N/C
- A spherical conductor is surrounded by two conducting shells
as shown in Fig. 4. The radius of the sphere is 1m. The inner radius
of the middle shell is 1.5 m, and the outer radius of the same shell
is 2m. Finally, the inner radius of the outside shell is 2.5 m,
and the outer radius of the outer shell is 3m. Given that the
electric field at r=1.2m is 6.24x103 N/C, the charge on the inside
of the outer shell is 7.00x10-6 C, and the net charge on the outer
shell is 6.00x10-6 C, what is the electric field at r=2.3m in N/C?
(We are using the convention that the electric field is positive
going away from the center of the sphere and negative going towards
the center.)
- -12000 N/C
- -10200 N/C
- +1700 N/C
- +10200 N/C
- +12000 N/C
- In Fig. 5, which point, P2 or P3, has (i) the higher potential energy
for an electron and (ii) the higher electrical potential for an electron?
(The charge densities are the same as for Fig. 3:
sigma 1 = -8x10-9 C/m2 ,
sigma 2 = -8x10-9 C/m2 , and sigma 3 = 2x10-9 C/m2 .)
- (i) P2, (ii) P2
- (i) P2, (ii) P3
- (i) P3, (ii) P2
- (i) P3, (ii) P3
- None of the other answers is correct.
- If the current through R4 in Fig. 6 is 4A, what is the
net current, I, through the whole network?
- 15 A
- 16 A
- 17 A
- 18 A
- 19 A
- In the circuit shown in Fig. 7, what is the voltage difference
VB - VD ?
- -24 V
- -4 V
- +4 V
- +12 V
- +24 V
- In the circuit shown in Fig. 8, each of the resistors are
light bulbs with identical resistance.
List the light bulbs from dimmest to brightest.
Group light bulbs with the same brightness in parentheses.
- dimmest (B),(AD),(CEF) brightest
- dimmest (B),(AD),(EF),(C) brightest
- dimmest (B),(CEF),(AD) brightest
- dimmest (B),(EF),(ACD) brightest
- dimmest (B),(EF),(AD),(C) brightest
- What is the effective capacitance of the circuit shown
in Fig. 9?
- 4.6 micro-F
- 5.3 micro-F
- 6.5 micro-F
- 7.4 micro-F
- 27 micro-F
- In the RC circuit shown in Fig. 10, what is the current
through R2 (a) immediately after the switch is closed,
(b) a long time after the switch is closed?
- (a) 0 mA, (b) 0 mA
- (a) 0 mA, (b) 6 mA
- (a) 0 mA, (b) 12 mA
- (a) 6 mA, (b) 0 mA
- (a) 12 mA, (b) 0 mA
- An electron travels in the x-y plane as shown in Fig. 11.
It experiences a force in the z direction due to a uniform
magnetic field.
Which of the following are possible directions for the magnetic field?
- The magnetic field can be in the x direction or the y direction.
- The magnetic field can be in the x direction or the -y direction.
- The magnetic field can be in the -x direction or the y direction.
- The magnetic field can be in the -x direction or the -y direction.
- The magnetic field can be in the x direction or the z direction.
- A proton moves perpendicular to an magnetic field of 3 Tesla.
How long does it take the proton to complete one orbit?
- 3.5 x 10-12 sec
- 2 x 10-11 sec
- 2 x 10-9 sec
- 3.5 x 10-9 sec
- 2 x 10-8 sec
- Two wires with current flowing perpendicular to the
plane of the page produce the magnetic field lines shown in Fig. 12.
Which direction is the current moving in each wire?
- into the page for wire A, into the page for wire B
- into the page for wire A, out of the page for wire B
- out of the page for wire A, into the page for wire B
- out of the page for wire A, out of the page for wire B
- None of the other answers is correct.
- In Fig. 13 (a) the current in the outer loop is going clockwise
and decreasing. (a) What is the direction of the induced current
in the inner loop? In Fig. 13 (b) the current in the wire is
moving down and increasing. (b) What is the direction of the
induced current in the loop to the left of the wire?
- (a) clockwise, (b) clockwise
- (a) clockwise, (b) counterclockwise
- (a) counterclockwise, (b) clockwise
- (a) counterclockwise, (b) counterclockwise
- None of the other answers is correct.
- Light is incident at angle A from a media with n = 1.5
to one with n = 2.0 as shown in Fig. 14. What is the minimum value for A
so that there is total internal reflection at point P, which is at the
interface between the n = 2 and n = 1 materials?
?
- 25 degrees
- 30 degrees
- 35 degrees
- 42 degrees
- 49 degrees
- An object of height 5 cm is placed 30 cm in front of spherical concave
mirror. If the image is real and 10 cm high, what is the radius of
curvature of the mirror?
- 10 cm
- 20 cm
- 40 cm
- 60 cm
- 120 cm
- Two lenses are placed on the x-axis. The first lens is a diverging
lens with focal length 4cm placed at x = -2cm.
The second lens is a converging lens with focal length 7cm placed at x = 8cm.
If an object is placed at x = -18cm, what is the position of the image
on the x-axis? (Choose the closest answer.)
- x = 11 cm
- x = 15 cm
- x = 19 cm
- x = 21 cm
- x = 23 cm
- In the above problem, which of the following characterizes the
final image when compared to the original object?
- real, upright, and larger
- real, upright, and smaller
- real, inverted, and larger
- real, inverted, and smaller
- virtual, upright, and larger
- Place your name, social security number, and exam number on
your bubble sheet -- NOW. Also, print and sign your name on the
exam printout.
- Done correctly.
- Done incorrectly.
- Done incorrectly.
- Done incorrectly.
- Done incorrectly.
Answers
- Answer = (3) The electroscope can have an overall positive charge, if the rod is a positively charged insulator.
- Answer = (2) 1490 N
- Answer = (3) 176 degrees
- Answer = (3) -113 N/C
- Answer = (1) -12000 N/C
- Answer = (2) (i) P2, (ii) P3
- Answer = (4) 18 A
- Answer = (2) -4 V
- Answer = (5) dimmest (B),(EF),(AD),(C) brightest
- Answer = (1) 4.6 micro-F
- Answer = (4) (a) 6 mA, (b) 0 mA
- Answer = (2) The magnetic field can be in the x direction or the -y direction.
- Answer = (5) 2 x 10-8 sec
- Answer = (3) out of the page for wire A, into the page for wire B
- Answer = (2) (a) clockwise, (b) counterclockwise
- Answer = (4) 42 degrees
- Answer = (3) 40 cm
- Answer = (5) x = 23 cm
- Answer = (4) real, inverted, and smaller
- Answer = (1) Done correctly.