A long conducting cylindrical rod is inside a long conducting enclosure with a s

Question

A long conducting cylindrical rod is inside a long conducting enclosure with a square cross-section as shown to the right.

The rod is maintained at a potential of +5000 volts with respect to the square which is grounded (V=0). The contour lines are equipotentials at V = +4000, +3000, +2000, and +1000 volts.

Select a response for each statement below. (Use 'N', North, towards top of page (+y dir), and 'E', East, to the right (+x dir), 'NE' for in between 'N' and 'E', etc.)
1. The direction of the force on a small (-) charge at 9 is ....

2. The y-component of the E-field at 4 is negative.

3. The direction of the force on a small (+) charge at 9 is ....

4. The direction of the E-field at 5 is ....

5. The magnitude of the E-field at 7 is greater than that at 4

6. The y-component of the E-field at 7 is zero.

7. The magnitude of the E-field at 1 is very small (~ zero).

The answers I have are but either 1 or more is apparently wrong :

1. N

2. False

3. S

4. SW

5. False

6. True

7.False

Explanation / Answer

1 N. Straight up.

2 False. The E field is directed NW so the y-component is positive.

3. S. Straight down.

4. SW (at point 5)

5. False. The equipotentials are closer together at point 7 so the voltage change per meter is greater there.

6. True. The field is pointed directly in the positive x direction there.

7. True, E fields inside a conductor are zero.

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