Please remember that I'm not a science or physics student, so please explain as simply as you can. Thanks. In the case of DC current electrons flow from a negative terminal to a positive. A negative terminal is full of electrons and the positive is electron deficient. I'm trying to understand how AC current flows. It is said AC switches on and off several times a second, let's saying it's 50 times. Now please have a look on the linked diagram: http://img405.imageshack.us/img405/4516/howacworks.jpg Does that 50 times on/off mean that A (or B) changes its polarity 50 times in one second? When A is +ive, B is -ive. When B is +ive, A is -ive. Please help me to understand this. Thank you.