Which of the following increases the strength of an electric motor's magnetic field?

Increasing the current and the number of turns in the coils enhances the strength of an electric motor's magnetic field due to the principles of electromagnetism.

When an electric current flows through a wire, it generates a magnetic field around that wire. The strength of this magnetic field is directly proportional to the amount of current flowing. By increasing the current, you amplify the magnetic field strength.

Moreover, wrapping the wire into coils and increasing the number of turns significantly strengthens the magnetic field as well. Each loop of wire contributes to the total magnetic field, and thus, more loops result in a greater combined effect. The magnetic fields from each coil add together, leading to an overall stronger magnetic field. This principle is fundamental to the operation of electric motors, where a robust magnetic field is necessary for effective motion and force generation.

Both aspects—higher current and more turns—work in tandem to boost the magnetic field strength, making the motor more efficient and powerful in its operation.