Why does terminal voltage change when current flows through a real battery?

[Tanishq Nandan]

Hey,
My question isn't exactly a problem,it's just a doubt which occurred in my mind,while studying current electricity.The potential difference across the emf of an ideal battery is considered to be constant,whereas if the battery has an internal resistance (the case for all real life batteries),the potential difference across it's terminals changes as soon as a current flows through it.

What is the exact reason for this??

 

[ehild]

Hey,
My question isn't exactly a problem,it's just a doubt which occurred in my mind,while studying current electricity.The potential difference across the emf of an ideal battery is considered to be constant,whereas if the battery has an internal resistance (the case for all real life batteries),the potential difference across it's terminals changes as soon as a current flows through it.

What is the exact reason for this??

The current flows through the internal resistance, and causes potential drop across it.

 

[Tanishq Nandan]

The current flows through the internal resistance, and causes potential drop across it.

Oo..that simple?
K,thanks

 

[CWatters]

Yes that simple.

Just for info... The internal resistance isn't always constant. Sometimes a used AA cell will read 1.2-1.4 V on a volt meter even though it's nearly empty. But if you try and draw any significant current from it the voltage falls much further than it would if the battery was new/full. The internal resistance has increased as the cell was used. The internal resistance of a cell can also vary with cell temperature. All this means that measuring the voltage of a cell isn't necessarily a good indication of how much energy is left in it.