An electric fan rotates due to the interaction between the electric motor's electromagnetic field and its stationary magnetic field. When electricity is supplied to the motor, it creates a rotating magnetic field, which in turn induces a current in the fan's blades, causing them to spin.

The rotation of an electric fan is a result of the principles of electromagnetic induction and the conversion of electrical energy into mechanical energy. When the fan's motor is powered on, an alternating current (AC) flows through the motor's windings, creating a magnetic field. This magnetic field interacts with the permanent magnets or electromagnets within the motor, causing the motor's shaft to rotate. The fan's blades are attached to this shaft, so as the shaft rotates, the blades move, creating air movement.

According to the National Electrical Manufacturers Association (NEMA), the average household fan consumes about 70 watts of power. This energy is converted into mechanical energy that moves the fan's blades. The efficiency of this conversion is influenced by various factors, including the design of the motor and the fan's aerodynamic shape.

The efficiency of an electric fan's motor can be estimated using the following formula:

Efficiency = (Power Out / Power In) 100

Where Power Out is the mechanical power delivered to the fan blades and Power In is the electrical power consumed by the motor. Modern electric fans typically have an efficiency of around 60-70%, meaning that approximately 60-70% of the electrical energy is converted into mechanical energy, while the rest is lost as heat.

The design of the electric fan also plays a crucial role in its performance. For instance, a fan with a higher blade pitch (the angle between the blades) will move more air at a lower speed compared to a fan with a lower blade pitch. This is because a higher blade pitch creates a more efficient airflow, which can be achieved with less energy.

In conclusion, an electric fan rotates due to the electromagnetic induction principle, where the interaction between the motor's electromagnetic field and its stationary magnetic field causes the motor shaft to rotate. This rotation is then transferred to the fan's blades, creating air movement. The efficiency of this process is influenced by the motor's design and the fan's aerodynamic shape, with modern fans typically achieving an efficiency of 60-70%.