A2L Item 236

• Description: Identify the effects on a conducting bar moving through a magnetic field on rails.
• Goal: Hone understanding of Faraday's Law
• Source: 283-710 Conducting bar on rails
• Keywords: Flux, Electromagnetism, Electric Field, Magnetic Field

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The question for students:

A conducting bar is placed on a set of horizontal rails. After a uniform magnetic field is set up perpendicular to the rails, the bar is given a push. As the bar moves along the rails, which of the following statements are true.

1. There is an E field in the bar
2. There is a current in the bar
3. The bar moves with a constant speed

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 are true

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Commentary for teachers:

Answer

(4) In the absence of a force sustaining the motion, the bar slows down. It is interesting to discuss what happens to the kinetic energy as the bar slows down. Advanced students can work out that the energy is dissipated in the resistance of the bar.

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