Problem 4: who is right? Two parallel, infinite planes of charge have charge densities +20 and -o as shown in Fig. O They are at a distance Lo from each other. Three students are asked to determine the electric field at points A and B, at a distance L above the top plane, and at a distance L below the bottom plane, respectively, as shown in the figure. Each student comes up with a different answer and a different explanation. Read carefully their statements below. The students are reminded that the electric field magnitude of an infinite plane of charge with charge density o is E = +26 +26 Figure 1: Two equivalent views of the two infinite parallel planes • Student 1 draws the sketch in Fig. 2 (top) and says: "I think from the outside we can think of the two planes as a single infinite plane with charge density +20 - oa =a, so then we know the electric field must be a/(2o) pointing upwards at point A and also a/(2co) pointing dounwards at B". • Student 2 draws the sketch in Fig. 2 (middle and says "I don't agree with you, I think you need to consider the effect of each single plane, so at point A there will be a field upwards due to the top plane with magnitude 20/(2ro) = a/ea, and at point B there will be a field upuards due to the bottom plane with magnitude a/(2o)". • Student 3 draws the sketch in Fig. 2 bottom and says "Do we just add the electric fields together? I'm going magnitude a/ea +a/(2eo) = 30/(2ro), and at point BI get the same 30/(2eo) but now pointing dounward" add up the field from each plane at both points. So at A I get a field upward of Evaluate each student's statement. Decide whether or not the statement is correct. If the student explanation contains incorrect reasoning, explain how the argument is flawed. studets 1%. 국 +936-6) student 2 studeut 3 % up +1 = 32 down Figure 2: Students' sletches.
Problem 4: who is right? Two parallel, infinite planes of charge have charge densities +20 and -o as shown in Fig. O They are at a distance Lo from each other. Three students are asked to determine the electric field at points A and B, at a distance L above the top plane, and at a distance L below the bottom plane, respectively, as shown in the figure. Each student comes up with a different answer and a different explanation. Read carefully their statements below. The students are reminded that the electric field magnitude of an infinite plane of charge with charge density o is E = +26 +26 Figure 1: Two equivalent views of the two infinite parallel planes • Student 1 draws the sketch in Fig. 2 (top) and says: "I think from the outside we can think of the two planes as a single infinite plane with charge density +20 - oa =a, so then we know the electric field must be a/(2o) pointing upwards at point A and also a/(2co) pointing dounwards at B". • Student 2 draws the sketch in Fig. 2 (middle and says "I don't agree with you, I think you need to consider the effect of each single plane, so at point A there will be a field upwards due to the top plane with magnitude 20/(2ro) = a/ea, and at point B there will be a field upuards due to the bottom plane with magnitude a/(2o)". • Student 3 draws the sketch in Fig. 2 bottom and says "Do we just add the electric fields together? I'm going magnitude a/ea +a/(2eo) = 30/(2ro), and at point BI get the same 30/(2eo) but now pointing dounward" add up the field from each plane at both points. So at A I get a field upward of Evaluate each student's statement. Decide whether or not the statement is correct. If the student explanation contains incorrect reasoning, explain how the argument is flawed. studets 1%. 국 +936-6) student 2 studeut 3 % up +1 = 32 down Figure 2: Students' sletches.
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![Problem 4: who is right?
Two parallel, infinite planes of charge have charge densities +20 and -o as shown in Fig. 1 They are
at a distance L, from each other. Three students are asked to determine the electric field at points A
and B, at a distance L above the top plane, and at a distance L below the bottom plane, respectively, as
shown in the figure. Each student comes up with a different answer and a different explanation. Read
carefully their statements below.
The students are reminded that the electric field magnitude of an infinite plane of charge with charge
density a is E = .
+26
3+26
Figure 1: Two cquivalent views of the two infinite parallel planes
• Student 1 draws the sketch in Fig. 2 [top] and says: "I think from the outside we can think of the
two planes as a single infinite plane with charge density +20 - o =0, so then we know the electric
field must be a/(2) pointing upwards at point A and also o/(2c) pointing doumwards at B".
• Student 2 draws the sketch in Fig. 2 middle and says "I don't agree with you, I think you need
to consider the effect of each single plane, so at point A there will be a field upwards due to the
top plane with magnitude 20/(2eo) = a/eo, and at point B there will be a field upwards due to the
bottom plane with magnitude a/(2eo)"
• Student 3 draws the sketch in Fig. 2 bottom) and says "Do we just add the electric fields together?
I'm going to add up the field from each plane at both points. So at A I get a field upward of
magnitude a/eo +a/(2eo) = 30/(2ro), and at point BI get the same 30/(2eo) but now pointing
downward"
Evaluate each student's statement. Decide whether or not the statement is correct. If the
student explanation contains incorrect reasoning, explain how the argument is flawed.
studats
11111 1&.
student 2
student 3
½ up
%3D
3, down
Figure 2: Students' sketches.
blue
口
-](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F1606b766-bfa8-4083-9557-a4bb20db7c66%2Ff82e253f-05ff-4a53-9ec4-86a1bf748d6d%2Fak27a4_processed.jpeg&w=3840&q=75)
Transcribed Image Text:Problem 4: who is right?
Two parallel, infinite planes of charge have charge densities +20 and -o as shown in Fig. 1 They are
at a distance L, from each other. Three students are asked to determine the electric field at points A
and B, at a distance L above the top plane, and at a distance L below the bottom plane, respectively, as
shown in the figure. Each student comes up with a different answer and a different explanation. Read
carefully their statements below.
The students are reminded that the electric field magnitude of an infinite plane of charge with charge
density a is E = .
+26
3+26
Figure 1: Two cquivalent views of the two infinite parallel planes
• Student 1 draws the sketch in Fig. 2 [top] and says: "I think from the outside we can think of the
two planes as a single infinite plane with charge density +20 - o =0, so then we know the electric
field must be a/(2) pointing upwards at point A and also o/(2c) pointing doumwards at B".
• Student 2 draws the sketch in Fig. 2 middle and says "I don't agree with you, I think you need
to consider the effect of each single plane, so at point A there will be a field upwards due to the
top plane with magnitude 20/(2eo) = a/eo, and at point B there will be a field upwards due to the
bottom plane with magnitude a/(2eo)"
• Student 3 draws the sketch in Fig. 2 bottom) and says "Do we just add the electric fields together?
I'm going to add up the field from each plane at both points. So at A I get a field upward of
magnitude a/eo +a/(2eo) = 30/(2ro), and at point BI get the same 30/(2eo) but now pointing
downward"
Evaluate each student's statement. Decide whether or not the statement is correct. If the
student explanation contains incorrect reasoning, explain how the argument is flawed.
studats
11111 1&.
student 2
student 3
½ up
%3D
3, down
Figure 2: Students' sketches.
blue
口
-
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