When it comes to stopping the operation of an electronic device, is there any difference between the two phrases?
As to "turn off", what devices that needs no electricity to work such as "tap" can be its objective? (Ex: I turned off the tap.)
I can't think of any except "tap".
Not a teacher.
I would say, especially concerning electric devices, that whenever a device is turned off by use of a switch, then turning off and switching off are the same.
Regarding your second question, you could turn off a car or a lawn mower or other internal-cumbustion engine. You could also turn off gas lighting, a gas stove, etc.