Today I learned why there’s a tingling sensation from the metallic body of, say, a MacBook when it’s charging. The effect is called electrovibration, and it arises due to parasitic capacitive coupling and the absence of grounding in the standard power supply. This seemed kind of obvious, but exactly how it works was not.
Inside the charger, there is a capacitor, which allows a safe but noticeable potential of AC current to seep into the aluminum laptop case. When you touch the cover, your body and the laptop become a sort of living capacitor, with a thin layer of aluminum and skin acting as an insulator that separates the charges.
The pulsation of current in the socket – 50-60 Hz. The electric field between the finger and the body sometimes strengthens, sometimes weakens. According to Coulomb’s Law, this causes the skin to be attracted to the metal and then released. If you simply rest your hand on the laptop, the force of this attraction is too small to notice.
It results in sensory deception – nerve endings in the finger pads, which in nature are responsible for recognizing textures, go haywire from such microscopic friction chaos. The brain is completely unable to directly recognize electrostatic microcurrents, so it chooses the most logical interpretation for itself and convinces you that it’s the metal itself that is vibrating.
Hi, I'm Rauf Aliev. 