Is it ok to fill an electric kettle straight after it's been emptied? I heard that it does something to the element. Please help!
Shock cooling anything is never good, strictly speaking, but whether there is serious harm in practice will depend on many factors. Refilling a hot kettle with cold water immediately after emptying probably will not make that much of a difference to the longevity of it.
If you are excessively cautious and a bit pedantic, I would say completely emptying a hot kettle will create more problems, such as increase of scaling especially if you have hard water and iron piping or corrosion. There is far more shock cooling from the last few drops of hot water evaporating off the element. I would not worry too much about refilling straight after. If you really do care, it would be more beneficial to not drain it of hot water to the point of exposing the element out of water.
Additionally, if you have limescale in your kettle (either on the element or the inside of the kettle), the cold shock may cause that to come off. Whether you want that, is up to you.
I used this with a non-electric kettle to get rid of the limescale
(put it on the heat, let it dry out and heat up, then immediately pour in water from the tap).