JAMB - Physics (1984 - No. 28)
The electromotive force obtained from a simple dynamo may be increased by
increasing the cross-sectional area of the coil
winding the coil on a soft-iron armature so as to decrease the magnetic flux through the coil
increasing the speed of rotation
making the field magnet longer
using low-resistance copper coils
Forklaring
Increasing the rotation speed enhances the electromotive force (EMF) generated due to Faraday's law of electromagnetic induction.