An electric motor includes a rotating part called the 1. , made of a coil of wire wound around an armature and placed inside the 2. , which is a permanent magnet. When current is applied, the rotor rotates between the poles of the permanent magnet. The rotation creates a 3. , which spins a 4. that transmits 5. energy to the device. There are two main types of electric motors. In 6. motors the direction of current is constant, so a 7. is needed to reverse it; in older motors it is connected to the rotor through 8. . In 9. motors, on the other hand, the 10. of current is automatically reversed.
5. Complete the text with the correct phrases taken from it and given below.
• and an electromagnet • almost every mechanical movement that you see around you • provided it is used under normal operating conditions. • whether AC or DC is chosen • electric motor. • require less maintenance • learn a lot about magnets • will attract the south end of the other. • Inside an electric motor • into mechanical energy • you know about the fundamental law of all magnets: • alternating current.
How an Electric Motor Works Electric motors are everywhere. In your house, 1. is caused by an AC (alternating current) or DC (direct current) 2. . By understanding how a motor works, you can 3. , electromagnets, and electricity in general. An electric motor uses magnets to create motion. If you have ever played with magnets, 4. opposites attract and likes repel. So, if you have two bar magnets with their ends marked “north” and “south”, then the north end of one magnet 5. On the other hand, the north end of one magnet will repel the north end of the other (and south will repel south). 6. , these attracting and repelling forces create rotational motion. A very small electric motor has two small permanent magnets, 7. a commutator, two brushes, made by winding wire around a piece of metal. It works the same way a larger version does, but on a much smaller scale. A DC electric motor converts direct current electrical energy 8. , unlike the AC version that uses 9. . Under test conditions, an electric motor can last between 15 to 20 years, 10. AC motors are generally more powerful and 11. than DC motors; however, DC motors tend to be more efficient. The type of application requiring the electric motor tends to influence 12.
6. Listen to the recording and create a brief summary that includes the differences between an AC and a DC motor, following the prompts.
• Power source • Commutation • Speed control • Starting torque • Efficiency • Maintenance
aperta
Soluzione suggerita:An AC motor runs on alternating current directly from the electrical grid and does not require commutation, whereas a DC motor uses direct current from batteries or rectified AC and relies on a commutator with brushes. When starting up, a DC motor offers a starting torque six times higher than an AC motor, and its speed is easily controllable, while controlling the speed of an AC motor is more challenging. In terms of performance, AC motors are better suited for high-power applications and large-scale industrial use, while DC motors are more efficient at lower power levels and in smaller devices. Finally, regarding upkeep, AC motors require lower maintenance, whereas the physical brushes in DC motors lead to more frequent maintenance.