This potential difference is also called voltage. The SI unit of potential difference is “Volt” and it is denoted by V.

1 Volt = 1 Joule/1 Coulomb

1V = 1J/C

• What is the direction of electric current in terms of potential difference?
• Do positive charges move in a conductor? Can you give an example of this?

Let us recall your experience of electrolysis and electroplating and conductivity of fluids that you had learned in earlier classes. When electric current is allowed to pass through fluids, the positive ions (cations) and negative ions (anions) move in opposite directions. The direction of the motion of positive charges in an electrolyte is always in the direction of the electric field while negative charges move in a direction opposite to that of positive charges. Thus for conduction in fluids there exists motion of both positive and negative charges. Whereas in case of metal conductors there will be only motion of electrons. (The positive charges are fixed in the lattice)

If positive charges move from point A to B in a conductor, the electric field does positive work so W/q is positive for free positive charges. You can say that the direction of the electric field is from A to B and the point A is at high potential and point B is at low potential. As negative charges always move in a direction opposite to the electric field we consider that electrons move from low potential to high potential.

We know that in a battery or cell a constant potential difference is maintained till the battery is completely discharged.

• How does a battery maintain a constant potential difference between its terminals?

• Why does the battery discharge when its positive and negative terminals are connected through a conductor?

To answer this, we need to know about how a battery or a cell works. A battery consists of two metal plates (electrodes) and a chemical (electrolyte). The electrolyte (chemical) between the two metal plates consists of positive and negative ions which move in opposite directions (see figure 6). The electrolyte exerts a certain force on these ions and makes them move in a specified direction. Let us call this force as a chemical force (Fc ). Depending upon the nature of the chemical, positive ions move towards one of the plates and accumulate on that plate. As a