✔ 最佳答案
1. When the cable is pulled at constant speed across a uniform magnetic field, the conducting cable cuts magnetic field lines. In so doing, free electrons inside the conducting cable are driven to one end of the cable (the force in pushing the electrons under such situation is called Lorentz force). Since movement of charges (free electrons) constitutes an electric current, there will then be a current flowing along the cable. This phenomenon is called electromagnetic induction.
As long as the cable is pulled, the electromagentic induction process goes on and a steady current is maintained in the cable. The electrical energy so produced is, in fact, comes from the work done by the pulling force.
2. A spring loaded switch is jsut one that when you press the switch button to switch on the circuit, a spring is also compressed. Whence, when you press the button again, the spring will automatically release the button to switch off the circuit.
2010-11-18 17:03:42 補充：
It is GIVEN in the question that there exist a current. This imples that a complet circuit is formed.
The pulling force is NOT directly acting on the electrons. It acts on the cable. That is, it does work on moving the cable....(contd)
2010-11-18 17:04:09 補充：
(cont'd).... Such motion induced an emf and current. The electrons are compelled to move by electromagentic forces. There involves an energy transformation from mechanical to electrical energy.
