A2L Item 234

• Description: Identify the correct statement(s) regarding the force between two current carrying wire segments.
• Goal: Reason regarding forces between current elements
• Source: 283-660 Force between two wires
• Keywords: Current, Electromagnetism, Forces, Magnetic Field

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The question for students:

A very long wire lies in a plane with a short wire segment. The long wire carries current I, while the short wire of length L carries current i. The two wires are parallel to each other. Which of the following statements are true?

1. The direction of the magnetic force exerted by the long wire on the short wire is directed away from the long wire.
2. The magnitude of the force on the short wire is μ₀IiL/2πd.
3. The long wire experiences a force of exactly the same magnitude as the force experienced by the short wire.

1. A only
2. B only
3. C only
4. A and B
5. A and C
6. B and C
7. A, B, and C
8. None of them are true

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Commentary for teachers:

Answer

(6) The force is attractive between the wires so statement A is false. Students need to interpret the phrase ‘very long’ as implying that the wire is infinite.

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