Question

Why potential difference is greater than emf during charging?

Answer 1

During the charging process of a battery, the potential difference across the terminals of the battery can be greater than the electromotive force (EMF) of the battery. Here's why:

1. EMF of the Battery:
   

   - The EMF is the voltage that the battery is designed to provide when no current is flowing. It represents the maximum potential difference the battery can deliver under ideal conditions (when it's not connected to a load or during charging).

1. Charging Process:
   

   - When a battery is being charged, an external power source (like a charger) is connected to the battery. The charger applies a voltage that forces current to flow into the battery, reversing the chemical reactions that occur when the battery discharges.
   - The external power source must overcome not only the internal resistance of the battery but also the voltage already present across the battery’s terminals (the potential difference).

1. Why the Potential Difference is Greater:
   

   - As the battery charges, the current flowing into the battery causes a voltage drop across the battery’s internal resistance. This means that the total potential difference across the battery's terminals becomes higher than the EMF.
   - The charging voltage (provided by the charger) is higher than the EMF in order to push the current into the battery. This is required because the charger needs to "fight" against the battery’s internal resistance and also overcome the potential difference already present in the battery.
   - Essentially, the charger provides a higher voltage than the EMF to push current into the battery and store energy.

In summary, the potential difference is greater than the EMF during charging because the charger applies a higher voltage to overcome the internal resistance of the battery and the voltage present inside the battery, ensuring that the battery gets charged.