In: Electrical Engineering
correct option is
(4). "current is the movement or flow of electrons in a circuit".
Let us understand Current.
The flow of electrons from one atom to another atom is known as current and is designated with symbol ‘I ‘.
The amount of current flowing is determined by number of electrons that pass through a cross section of conductor in one second. Due to very small size of atoms, it takes about 10^24 electrons to fill one cubic centimeter of a copper conductor. Trying to represent small value of current in terms of electrons would be very difficult. That is why current is represented as Ampere.
A current of one ampere means, in one second 6.24 X 10^18 electrons move through a cross section of a conductor.
When discussing current, the direction of current flow needs to be considered. There are two different theories about this:
Conventional Flow: This theory states that electrons flow from positive to negative. Benjamin Franklin theorized this when very little was known about electricity. It states that an invisible fluid known as electricity tended to flow through a wire from the positive to the negative. Ben’s theory became the convention (hence the term “conventional current”) in electrical theory, mathematics, textbooks and electrical equipment for the next hundred years.
Electron Flow: This theory states that electrons flow from negative to positive. When more was known about the behaviour of electrons, scientists discovered that electrons actually flow from negative to positive. Since electrons are negatively charged, it follows that they are attracted by positively charged bodies and repelled by negatively charged bodies.
Understanding Current with water analogy:
If we consider a water tank over the roof of residential house, the flow of water coming through tap can be visualized as equivalent to ‘Current’.
We can say in short that, the current is ‘flow of electrons’ in an electric circuit.