Question

factor on which strength of motor depends

Answer 1

he electric motor speed depends on both the applied voltage and the number of turns of its coil.
The more turns the motor has the higher the strength of the rotor magnetic field if the current is maintained constant. The problem is that, as you add turns, the electric resistance of the coil increases so you also have to rise the voltage to keep the current same as before.
As the strength of the magnetic field increases also the attraction - repulsion force of the rotor increases and in consequence its speed increases.

Answer 2

1.Number of turns of insulated copper wire
2.Strength of current