## Survey of E+M

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Two small objects, each with a net charge of +Q, exert a force of magnitude F on each other:

We replace one of the objects with another whose net charge is +4Q:

1. The original magnitude of the force on the +Q charge was F; what is the magnitude of the force on the +Q charge now?

4F                                   F
5F/2                               F/4
3F                                   None of the above
2F

2. What is the magnitude of the force on the +4Q charge?

4F                                   F
5F/2                                 F/4
3F                                   None of the above
2F

Next we move the +Q and +4Q charges to be 3 times as far apart as they were:

3. Now what is the magnitude of the force on the +4Q charge?

4F/3                                 F/9
4F/9                                 F/36
F/3                                     4F
5F/18                               None of the above
2F/9

4. Here are two charges of equal magnitude but opposite sign, separated by a distance s:
Choose from the following possible directions to answer the questions below:
What is the direction (a-j) of the electric field at location 1 (marked with an x)?

 a.   right g.   out b.   up-right h.   in c.   up i.   zero d.   up-left j.   None of the above e.   left f.   down

5. What is the direction (a-j) of the electric field at location 2 (marked with an x)?

 a.   right g.   out b.   up-right h.   in c.   up i.   zero d.   up-left j.   None of the above e.   left f.   down

6. A moving electron with charge -e travels along the path shown, and passes through a region of electric field. There are no other charges present. The electric field is zero everywhere except in the gray region.

Choose from the following possible directions to answer the question below:
What is a possible direction (a-g) of the electric field in the region where the field is non-zero?

a.   right
b.   up
c.   left
d.   down
e.   out
f.   in
g.   None of the above

7. A non-conducting wall is given a negative net charge. Next, a sheet of very flexible rubber with zero net charge is suspended from the ceiling near the charged wall as shown below.
The rubber sheet will:

not be affected by the charges on the wall since rubber is an insulator.
not be affected by the charged wall because the rubber sheet has zero net charge.
bend away from the wall due to the electrical repulsion between the electrons in the rubber and the charges on the wall
bend away from the wall due to the polarization of the rubber molecules by the charged wall.
bend toward the wall due to the polarization of the rubber molecules by the charged wall
none of the above

8. Salt water contains n sodium ions (Na+) per cubic meter and n chloride ions (Cl-) per cubic meter. A battery is connected to metal rods that dip into a narrow pipe full of salt water. The cross-sectional area of the pipe is A.

What is the direction of conventional current flow in the salt water?

To the right.
To the left.
There is no conventional current because the motions of the positive and negative ions cancel each other out.

9. The magnitude of the drift velocity of the sodium ions is vNa, and the magnitude of the drift velocity of the chloride ions is vCl. Assume that vNa > vCl. (+e is the charge of a proton)

What is the magnitude of the ammeter reading?

e n A vNa - e n A vCl
e n A vNa + e n A vCl
e n A vNa
e n A vCl
zero

10. A student has set up the three circuits shown. The light bulbs and the batteries are identical.

Rank all 3 ammeters (A1, A2, A3,) in order of their current measurements from greatest to smallest.

A1 = A2 = A3                   A3 > A1 = A2
A1 = A2 > A3                   A3 > A1 > A2
A1 = A3 > A2                   A3 > A2 > A1
A2 = A1 > A3                   None of the above
A2 = A3 > A1

11. In these three circuits, all the batteries are identical and have negligible internal resistance, all of the light bulbs are identical.

Rank all 5 light bulbs (A, B, C, D, E) in order of brightness from brightest to dimmest.

A = B = C > D = E           A = D = E > B > C
A > B = C = D = E           A > D = E > B = C
A > B = C > D = E           D = E > A > B = C
A > B > C > D = E           None of the above
A = D = E > B = C

12. Which of the following statements is true about the electric field inside the bulb filament?
The electric field must be zero because the filament is made of metal.
The electric field must be zero because a current is flowing.
The electric field must be zero because any excess charges are on the surface of the filament.
The electric field must be non-zero because the flowing current produces an electric field.
The electric field must be non-zero because no current will flow without an applied field.
The electric field must be zero for reasons not given above.
The electric field must be non-zero for reasons not given above.

13. The capacitor is originally charged. How does the current I in the ammeter behave as a function of time after the switch is closed?
I = 0 always.
I = constant (non-zero).
I increases, then is constant.
I instantly jumps up, then slowly decreases.
None of the above.

In a certain region of space there is a uniform electric field of magnitude E. Four points are marked by X's (labeled 1-4). They are separated by horizontal distance w and vertical distance h, as shown here:

Use this figure to answer the next three questions:

14. What is the potential difference V2 - V1 = ?
+Ew
-Ew
+Eh
-Eh

zero

15. What is the potential difference V3 - V1 = ?
+Ew
-Ew
+Eh
-Eh

zero

16. What is the potential difference V4 - V1 = ?
+Ew
-Ew
+Eh
-Eh

zero

17. What is the magnitude of the potential difference between points A and B on the circuit, while the switch is open?
0 volts
3 volts
6 volts
12 volts
None of the above

18. Here is a cylinder on whose surfaces there is a vertical electric field of varying magnitude as shown. The electric field is uniform on the top face with magnitude 800 V/m, and also uniform on the bottom face, but with a different magnitude, 400 V/m.
The cylinder encloses
no net charge.
net positive charge.
net negative charge.
There is not enough information available to determine whether or not there is a net charge inside the cylinder.

19. In static equilibrium, the potential difference between two points inside a solid piece of metal
is zero because metals block electric interactions.
is zero because the electric field is zero inside the metal.
is non-zero if the piece of metal is not spherical.
is non-zero if there are charges on the surface of the metal.
is non-zero for reasons not given above.
is zero for reasons not given above.

20. A proton is initially at rest in a region of constant magnetic field (show below). There are no other charges present.

Choose from the following possible directions to answer the question below:

What is the direction (a-h) of the initial magnetic force on the proton?

a.   right
b.   up
c.   left
d.   down
e.   out
f.   in
g.   zero force
h.   None of the above

21. Here is a bar magnet. The magnetic field made by the bar magnet at one location is shown in the diagram:

Choose from the following possible directions to answer the questions below:

What is the direction (a-j) of the magnetic field of the bar magnet at location 1 (marked with an X)?
 a.   right g.   out b.   up-right h.   in c.   up i.   zero d.   up-left j.   None of the above e.   left f.   down

22. What is the direction (a-j) of the magnetic field of the bar magnet at location 2 (marked with an X)?
 a.   right g.   out b.   up-right h.   in c.   up i.   zero d.   up-left j.   None of the above e.   left f.   down

23. A moving electron with charge -e travels along the path shown, and passes through a region of magnetic field. There are no other charges present. The magnetic field is zero everywhere except in the gray region.

Choose from the following possible directions to answer the questions below:

What is a possible direction (a-g) of the magnetic field in the region where the field is non-zero?
a.   right
b.   up
c.   left
d.   down
e.   out
f.   in
g.   None of the above

24. Two identical circular loops of wire, perpendicular to the page, carry the same conventional current I:
Choose from the following possible directions to answer the questions below:
In the front view, what is the direction (a-h) of the magnetic field due to the loops at location P, midway between the loops?
a.   right
b.   up
c.   left
d.   down
e.   out
f.   in
g.   zero field
h.   None of the above

25. Two wires lie in the plane of the page. Wire 1 carries conventional current to the left, and wire 2 carries conventional current to the right:
Choose from the following possible directions to answer the questions below:

What is the direction (a-h) of the magnetic force that wire 1 exerts on wire 2?
a.   right
b.   up
c.   left
d.   down
e.   out
f.   in
g.   zero force
h.   None of the above

26. A proton, moves with a constant velocity v to the right through a region where there is a uniform magnetic field of magnitude B that points into the page. There is also an electric field in this region. The magnetic field and electric field are produced by devices not shown on the diagram.
Choose from the following possible directions to answer the question below:
What is the direction (a-g) of the electric field in this region?
a.   right
b.   up
c.   left
d.   down
e.   out
f.   in
g.   None of the above

27. What is the magnitude of the electric field?
(Note: +e is the charge of the proton, and the question is asking for a magnitude )
 e v B vB/e v B e v B None of these

28. Here is a long solenoid (coils of wire along a cylinder), and an end view of the solenoid. Conventional current runs counter- clockwise in the solenoid and is increasing with time.
Choose from the following possible directions to answer the questions below:

What is the direction (a-h) of the electric field at location 1 (marked with an x)?
a.   right
b.   up
c.   left
d.   down
e.   out
f.   in
g.   zero field
h.   None of the above

29. What is the direction (a-h) of the electric field at location 2 (marked with an x)?
a.   right
b.   up
c.   left
d.   down
e.   out
f.   in
g.   zero field
h.   None of the above

30. A neutral metal bar is moving at constant velocity v to the right through a region where there is a uniform magnetic field pointing out of the page. The magnetic field is produced by some large coils which are not shown in the diagram.
Which of the following diagrams best describes the state of the metal bar?

a
b
c
d
e
f
g

A variable power supply is connected to a coil and an ammeter, and the time dependence of the ammeter reading is shown. A nearby coil is connected to a voltmeter.

31. Which of the following graphs correctly shows the time dependence of the voltmeter reading?

a
b
c
d
e
f

32. The next few questions refer to the circuit below in which four identical bulbs are connected to a battery. (The switch, S, is initially closed as in the diagram.)
Assume the battery is ideal (no internal resistance), and the connecting wires have no resistance. Unlike most real bulbs, the resistances of the bulbs do not change as the current through them changes.

Which of the following correctly ranks the currents flowing through the bulbs?
All bulbs have the same current flowing through them.
The current through 1 is largest, 2 next largest, 3 next largest, and 4 smallest.
The current thought 1 is largest, 2 is the same as 3, and each is smaller than 1. 4 is smallest.
The current through 1 and 4 is the same. 2 is the same as 3, and each is smaller than 1 or 4.
The current through 2 and 3 is the same. 1 is the same as 4, and each is smaller than 2 or 3.
The current through 1 is largest, 4 is next largest. 2 is the same as 3, and each is smaller than 4.
None of these is correct.

(Same situation described above)

33. Which of the following correctly ranks the potential differences across the bulbs?
All the bulbs have the same potential differences across them.
The potential difference across 1 is largest, 2 next largest, 3 next largest and 4 smallest.
The potential difference across 1 is largest. 2 is the same as 3, and each is smaller than 1. 4 is smallest.
The potential difference across 1 is the same as 4. 2 is the same as 3, and each is smaller than 1 or 4.
The potential difference across 2 is the same as 3. 1 is the same as 4 , and each is smaller than 2 or 3.
The potential difference across 1 is largest 4 is next largest. 2 is the same as 3, and each is smaller than 4.
None of these is correct.

34. What happens to the current through bulb 1 if the switch, S, is opened?
It increases.
It remains the same.
It decreases.
Not enough information is given.

35. How seriously did you just take this diagnostic exam?
I pretty much blew it off, didn't think much about a lot of the answers.
I took it sort of seriously, but when I didn't know an answer I didn't think very hard about it.