Originally posted by daisy_polly
The difference between conventional current and electron flow. Also explain why were these two conventions developed?
I'm assuming that, by conventional current, you mean the abstract idea that protons are positive and electrons are negative, and that this conventional current flows from high (positive charge) to low (negative charge).
The difference is very simply stated (but don't be discouraged that it didn't occur to you, because it's just one of those things that you have to be told):
Electrons flow in the opposite direction of conventional current. Why? Because the electron wasn't well enough understood at the time the convention was established.
One thing to note: the convention does not affect the physics of circuits, only the way you do calculations. It does come to issue when dealing with magnetism, which is how it was determined that the negative charges are actually the ones flowing (see the hall effect).
Originally posted by daisy_polly
How is direct current different from alternating current, ...
Direct current does not alternate (in polarity). Meaning, the direction that you draw the arrows on a circuit to represent the current do not change for direct current. Alternating current alternates (in polarity). Meaning, the side at which current enters a circuit element and the side at which current leaves a circuit element alternate periodically.
DC and AC also mean something more general than just referring to current. They are used in the most general sense to characterize any electrical signal, not just current (i.e. DC can mean a steady voltage level whereas AC would mean a voltage that varies periodically/sinusoidally).
Originally posted by daisy_polly
... why is the alternating current system chosen in Canada?
It is chosen everywhere in the world. It is chosen for the sake of power distribution. Loss occurs in transmission lines do to current. So, if you transmit the same amount of power at a lower current but higher voltage, then you don't lose as much power. The most effecient way to make the conversion is using transformers, but transformers only work with AC.
