all electrical equipment produce an EMF even the humble mp3 player albeit very low power hence the no electrical equipment rule ALSO the most dangerous part of any flight is take off and landing passengers should not be distracted so that they do not miss important [possibly life saving ] instructions from the aircrew

As stated above its more to do with take-off and landing being the most "risky" parts of the flight so they don't want people to be distracted in the case the worse happens. For example if you are listening to music with earphones, or watching a video and the crew need to pass urgent safety information....

joeseptuk ,

In addition to the above, any loose items in the event of an emergency becomes projectiles. With aircraft taking off or approaching at anything up to 200mph, any sudden changes in speeds would render something like an mp3 player or mobile phone a leathal projectile. The last thing you want is something whacking you in the back of your head. If you have your tray table down to put something like a laptop on, that would block and hinder your escape route in the event of an evacuation. Not only for yourself, but those sat adjacent to you. The main reason is distraction as mentioned above, ie situational awareness. Rules are there for a reason, for both aircraft and passenger safety.

Darren