Working of a battery

 

WORKING OF BATTERY:

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 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 result of this accumulation of charges on this plate it becomes positively charged (called anode). Negative ions move in a direction opposite to the motion of positive ions and accumulate on the other plate. As a result of this the plate becomes negatively charged (called cathode). This accumulation of different charges on respective plates continues till both plates are sufficiently charged.

         But the ions in motion experience another force , when sufficient number of charges are accumulated on the plates. Let us call this force as electric force (Fe). The direction of this force is opposite to the direction of chemical force Fc and the magnitude of this force depends on the amount of charge accumulated on the plates.

  The motion of ions continue towards their respective plates if the chemical force Fc is stronger than electric force Fe. 

The accumulation of charges on plates is continuous till the electric force Fe becomes equal to chemical force Fc. At this situation there will not be any motion in ions due to balance of forces Fe and Fc.

      It is shown in the new battery that we buy from the shop is at a stage where the ions in the electrolyte are under the influence of balanced forces. This is the reason for the constant potential difference between the terminals of a battery. The amount of charge accumulated on the plates depends on nature of the chemical used in the battery.

 What happens when the battery is connected in a circuit?

  When a conducting wire is connected to the terminals of the battery, a potential difference is created between the ends of the conductor. This potential difference sets up an electric field throughout the conductor (the direction of electric field is from positive terminal to negative terminal in the conductor).

We know that the conductor contains large number of electrons. The electrons near the positive terminal of the battery are attracted by it and start to move towards positive terminal. As a result, the amount of positive charge on this plate decreases. So the electric force Fe becomes weaker than chemical force Fc and chemical force pulls negative ions from the positive plate (anode) and makes them move towards the negative plate (cathode). The negative terminal pushes one electron into the conductor because of stronger repulsion between negative terminal and negative ion. Hence, the total number of electrons in the conductor remains constant during the current flow. The above said process continuous till equilibrium is attained between the forces Fe and Fc.

So, each and every time when the electron enters from wire to battery at positive terminal, Fc has to become stronger than Fe to drag that electron to negative terminal. In order to do so, Fc utilizes the chemical present in the battery. When all the chemical is utilized then the battery is exhausted, now again two forces come to equilibrium Fc=Fe.