3
votes
2answers
118 views

Why do batteries become weaker

I was thinking about my phone (Sony Xperia Z2) and when I put it to charge and remove it, the phone says "Please remove the charger, to save battery life," which is very intuitive question for a ...
4
votes
1answer
4k views

Why does it spark when I push a plug in the electrical socket?

When I slowly push a plug into the electrical socket I can often see sparks. Can anybody explain why? Can this be possibly harmful for the devices I plug in?