Which of the following factors increases the speed of an electric motor?

The choice of increasing the number of turns in the coils is correct because it directly impacts the strength of the magnetic field generated by the motor. When more turns of wire are wound in the coil, it creates a larger magnetic field for a given amount of current. This enhanced magnetic field results in a greater torque produced by the motor, which ultimately increases the speed at which the motor can operate.

The interaction between the magnetic field and the current flowing through the coils is what drives the motion in an electric motor. Thus, increasing the number of turns amplifies this interaction, leading to improved performance and speed.

In contrast, using a weaker power supply reduces the voltage and thus the current flowing through the motor's coils, which would decrease the motor's speed. Similarly, using a longer wire adds resistance to the circuit, which can also lower current and consequently reduce the speed of the motor. Reducing current limits the magnetic force and, in turn, the motor's rotational speed. Therefore, adding more turns to the coils is the most effective method among the options presented to enhance the motor's speed.