176 CHAPTER 20 Answers to Conceptual Questions 2. Consider the copper tube to be a large set of rings stacked one on top of the other. As the magnet falls toward or falls away from each ring, a current is induced in the ring. Thus, there is a current in the copper tube around its circumference. 4. The flux is calculated as cos B BA B A θ ⊥ Φ= = . The flux is therefore maximum when the magnetic field vector is perpendicular to the plane of the loop. We may also deduce that the flux is zero when there is no component of the magnetic field that is perpendicular to the loop. 6. No. Once the bar is in motion and the charges are separated, no external force is necessary to maintain the motion. An applied force in the x direction will cause the bar to accelerate in that direction. 8. As water falls, it gains velocity and kinetic energy. It then pushes against the blades of a turbine transferring this energy to the rotor or coil of a large alternating current generator. The rotor moves in a strong external magnetic field and a voltage is induced in the coil.
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