Ever Wondered What’s Inside This Bead At End Of Your Laptop Charger? Mystery Solved!

Ferrite beads

We all have a basic idea about the purpose of each wire going in and out of our computer. But a few wires seem a bit off when it comes to their appearance. They have a cylindrical bead dangling near the end. So what’s this bead doing on that wire and what purpose does it serve? Today, we are going to unravel this mystery for you.
Ferrite bead

You will not only find this bead at end of charging cables but also mouse, keyboard and other peripheral cables. It turns out that lump’s called a ferrite bead or, more generically, a choke. It’s a fancy name for what’s basically an electromagnetic wave-bouncer. If you open this bead, you will not find any complex circuits but only a ferrite cylinder that is magnetic in nature. It is this magnetic quality of the bead that serves the purpose.
Ferrite bead 2

So basically, when current passes through any cable, it generates electromagnetic interference (EMI). Your electronic gadgets also produce EMI during operation. For example, if you connect a camera to your monitor, the camera would produce intereference and cause your monitor to flicker without the presence of a ferrite bead. If left unabated, EMI can wreck havoc with your computer peripherals.
electromagneticMagnetic Field
These ferrite chokes ensure that signals are only sent in the intended directions and no EMI is transmitted between the peripherals. The choke dampens these EMI waves by acting as an EMI blocker. The blocking is most effective when it is near the source of the EMI, thats why you will only find these ferrite beads near the end of the cables. So, this little mystery is now solved! These tiny cyst-like beads make sure that our computer peripherals work properly and don’t cause any issues for the computer itself.



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    1. Yeah magnetic field is created when dc current flows through a wire and that’s what causes Electromagnetic interference. Same applies in case of ac current expect the fact the magnetic field changes direction as per ac current frequency.

    2. Yeah magnetic field is created when dc current flows through a wire and that’s what causes Electromagnetic interference. Same applies in case of ac current expect the fact the magnetic field changes direction as per ac current frequency

  1. Very nice… Only, one does not “wreck” havoc, one wreaks havoc… If you wrecked the havoc, that’s great! No more havoc, because you wrecked it, leaving only glorious harmony!

  2. What if i say the bead provided is for protection against an unexpected EXTERNAL magnetic fields as mentioned earlier the flow is DC so no effect from the inside for the outside.. as if its a usb cable 7 pins and 7 wires.. if it was like that it would interfere with one another as they are very closed.. nd no such bead like things are there..

    Final summation its to provide saftey against external fields interaction with the cable.. to avoid corruption of data..

    1. the Right Hand rule is for Electron fIow believe. That’s what the Navy teaches.

      The rest of the world uses Hole Flow. Electrons are negatively charged and therefore are opposite to the direction of current flow.

      I think the diagram is based on hole flow and therefore looks backward to you.

      I could be wrong. It’s happened before.

  3. I wonder y ppl r so interested in d mistake wht he has done regarding interpreation of magnetic field,, when they have such a neat explanation abt a major setup around dem to check out. Good job bro..!!

  4. Is this true when the laptop is running on battery? Why does the screen not flicker when one connects a camera when the laptop is running on battery?

  5. Boys……. magnetic field have nothing to do with hemisphere………….. Its universal for any point of earth geographic magnetic field is uni-directional… North-South poles of a magnet do not changes ….. on altering hemispheres…

  6. I think the direction of current and magnetic field shown in fig is wrong, it doesn’t obey right hand rule.
    kindly clear my doubt.

  7. may be your analysis is right my point of view that EMI is works has a choke which is controlled the up and down of voltage level and protect our computer like a auto transformer.

  8. It’s very real. I just clamped one onto the power cord of a guitar amplifier to stop RF interference. I was getting radio signals through my amp without it, and now I don’t.

  9. Does it matter what hemisphere your in? Could it be like water down a plug hole? Left hand or right hand depending on whether you are northern or southern…

  10. I must agree with Mr. Brennan. We all know that electromagnification and derivitives are actually a religion and not born out by real physics such as Jesus, pub etiquette, and the notion that one can actually believe it is butter. The “bead” is actually placed there to ensure when you pull the power cord towards you to continue whatever you were using your laptop for (and for 90% that will for accessing porn, 5% for ordering takeaway, 3% pressing “post comment”, 4% for eBay and Amazon shopping and 0.5% despising mathematics) that it snags a lamp, cup or family pet and causes carnage. Or it might not.

  11. Bollox… its just a grip to make pulling wire out easier! Electromagnetic interference hahaha. Cut it off, rewire it without and you’ll see theres no difference. Bellends!

    1. bren,

      due to faraday & lenzes law
      an induced current is made such that to oppose the change in magnetic flux.
      But I do understand your point with the right hand rule!

      1. Hmm very true! That would make much more sense – Althought if that were true then this article ought to be on wonderfulphysics.com b/c engineers never think of current like 😉

      2. It depends on wat type of current it is… Conventinal is right hand, while electron, or whatever u call the negitve flow, is left hand…. Since this is talking about an appliance and most appliances run off conventinal it is correct

        1. I’m sorry but I have to point out that an appliance can’t simply “choose” to just run on a specific type of current flow. All electrical energy that flows in this world no matter what, flows opposite to the direction of convention current, this is the electron flow, and no matter what it will always be the same, it doesn’t change simply because an appliance chooses to change it.

      1. Most Computer Peripherals are connected thru USB and flat 7 pin connector for monitor.The USB provides signal path as well as power to connected device. The Power Supplies in all peripherals use direct current (DC) and they are source of interference, while signals are of very negligible current train of voltage pulses (+ve DC Volt for “1” and no Volt for “0”). If no protection is provided in the form of ferrite bead, signal distortion and error creep into system. To provide immunity to signal from electromagnetic interference produced by Power Supply current pulses, tgese ferrite beads are used, as explained. The ferrite bead does not cause any problem to DC Current but dampens out noise produced by current pulses,