A2L Item 203

• Description: Indicate the charge situation that can account for a specified field constraint.
• Goal: Reason regarding electric fields
• Source: 283 -
• Keywords: Electromagnetism, Electric Field, Vectors

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The question for students:

Charge, Q, is at the origin. Points A-E are positions where other charges may be present. E_total at point F is non-zero and points in the +i direction. Which of the following situations could account for this?

1. Another charge is present at position A.
2. Two other charges are present at C & D.
3. Two other charges are present at D & B.
4. Two other charges are present at E & A.

1. A only
2. B only
3. C only
4. D only
5. A and B
6. A, C and D
7. A, B, and D
8. A, B, C, and D

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Commentary for teachers:

Answer

(2) Only a charge at C can counter the y component of the field of Q at F. A charge at B or D can then create a field at F that points in the i direction.

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