An engineer is testing a miniature wind-turbine prototype. The turbine features a rectangular armature coil of wire suspended between the opposite poles of two strong permanent magnets.
Initially, the armature coil is connected to a direct current (d.c.) power supply to test the apparatus as a motorized fan. When the current is switched on, the turbine blades begin to rotate. Explain why the coil rotates.
State two changes to the design of the turbine or the electrical circuit that would cause the blades to rotate at a higher speed when operated as a fan.
The power supply is then disconnected, and the armature coil is connected to a low-power light-emitting diode (LED) to form a complete circuit. When wind is blown onto the turbine, the blades spin. Explain why the LED lights up.