The Ferrite bead offers a high impedance to High frequency signals, thus stopping them from moving further up the circuit. These signals are attenuated as heat. This makes them useful in electronic equipment to filter EMI(Electromagnetic Noise)
Common sources of Electromagnetic noise are power cables in close proximity, earthing connections,
Ferrite Beads can be found in common electronic data cables and in cellphone cables. Ferrite beads can also be connected to cellphone headphones to block high frequency signals from reaching the earphones.