So it could follow the correct mass for the atom
The EMF of the battery includes the force to to drive across its internal resistance. the total resistance:
R = internal resistance r + resistance connected rv
R = r + rv
Now find the current:
V 1= IR
I = R / V1
find the voltage at the battery terminal (which is net of internal resistance) using
V 2= IR
So the voltage at the terminal is:
V = V2 - V1
This is the potential difference vmeter measured by the voltmeter.
Scientists use models to study atoms, Because atoms are very tiny, and almost impossible to cut open and look inside.. And the center of an atom is the nucleus and that is ever smaller.