Q. Why do we sometimes have to switch off our cell phones on a train?

A. Electronic appliances emit electromagnetic waves that can interfere with wireless transmissions of airplanes, TV stations and screens, and machines that control computers. Electromagnetic waves emitted from cell phones can cause someone's heart pacemaker to malfunction. The types of electromagnetic waves include short waves such as X-rays and longer waves like radio waves. An electromagnetic wave transmits very fast at a speed of about 300,000 km per second. It weakens as it travels longer distances. We have to switch off our cell phone when there is a possibility for strong electromagnetic waves disrupting someone's pacemaker.