Sometimes, I experience a tingling sensation on touching my MacBook while it's charging.
Recently, this became frequent and, got my attention. On touching my laptop, mild current finds its way through me to the ground. Electronics do this and, it's actually safer than we think (hopefully with laptops).
This post is going to be some everyday science. Current leakage, Potential difference, Ground pin - if you can't connect these words together, let's learn to.
Why I feel it?
Laptops have a metal enclosure which can conduct electricity. While charging, a small leakage may occur which can cause a laptop's exterior to gain potential. Thus while touching the metal enclosure, I close the circuit. The laptop has higher potential than ground and, as I'm between them touching both, a few milliamps current is set up to flow through me.
Laptop chargers output low voltage and considering the resistance of a human body, the current is too low to cause any harm (You won't be reading this otherwise). Also, home circuits will have a circuit breaker (tripper) to save you while things get worse.
I grabbed a wooden chair and, the sensation disappeared the moment I lifted my legs above the ground. (Legs down, feel the electrons. Legs up, nothing)
The extra pin
This is more of a discomfort than a safety issue. That's why we use a 3-pin plug to connect appliances to the electrical socket. The top large pin is the ground pin which literally connects to ground.
If by some means we connect the laptop exterior to the ground, then the electrons will take the low resistance path avoiding us. The laptop exterior is connected to the ground pin through the charger. All the ground pins are connected to a metal rod buried underground somewhere near your house.
Science tells me that I am not supposed to feel the current if I use a 3-pin connector. But I do use a 3-pin connector. Opening up the wall socket board which I use in my home, I found no wires connected to the ground pin back of the socket.
To the electrician,
How to take revenge on the laptop
It's not that only we get electrical shocks. We can give an electric shock to our laptop. (I bet, this is new to you)
"We develop static charges by rubbing our hand against a balloon" - remember seeing this in your school book. Static charges get developed on us during day-to-day activities. If we touch any internal computer parts, we may spoil it because of this phenomenon called Electrostatic discharge (ESD).
Internal Hard disk, RAM chips, and other such things are shipped inside an anti-static bag for this reason. Professionals while fixing your laptop, use ESD wrist strap or grounding mat which connects your hand to the ground.
Next time while opening up your CPU, remember that there exists a possibility of you spoiling it :P
Happy science :)