What is this small cylindrical thing on most power adapters ??

Over the last few months I've been intrigued to learn a lot about all sorts of electronic stuffs. Things which I used to play with on a daily basis became my subjects of exploration. I guess mostly its because of my new job where I'm surrounded by geeks and nerds. And being in the RF Engineering dept I think its important to know about each and every electronic circuit, or atleast have an understanding about the circuitry. And thats how I stumbled across the Ferrite beads.

I'm surprised that even though I've been using power adapters, and various cables connecting to computers and other equipments, never once did I ask myself, "What the hell is this ugly cylinder doing in the cable ??". I guess I was self contended in assuring myself that Ignorance is bliss. Not anymore though.

So now for some technical mumbo jumbo. The small cylinders are nothing but ferrite beads, sometimes called Chokes. Their main function is to reduce RF or Electromagnetic interference. The purpose is to suppress Common Mode Noise. Let me paint a clearer picture. Computers have Oscillators in them which can potentially broadcast radio signals at their frequencies. This makes them noisy(interferers). Also because of the length of the cables which makes them long antennae, they can now carry these signals. The signals can very well interfere with TV and radio. The cables due to the same antenna property can also receive signals and trasmit them into the computers/laptops. Thus ferrite chokes/beads are placed at the end of the cables to eliminate the RF interference. They have the function of capturing or choking the signals and convert them to heat.

Heyy now we've learnt something new :).