A question on the thevenin equivalent?

Question

When a current of 0.1A is drawn from a fresh AA-size manganese-alkaline cell, the terminal voltage is observed to fall from 1.50-1.48V.

1) Give a Thevenin equivalent for the cell

2) Hence estimate the cells short-circuit current. What is the terminal voltage under short-circuit conditions?

Answer 1

The Thevenin equivalent circuit is a source of emf (Eth) in series with a resistance (Rth)

With no current flowing, there is no p.d. across Rth so Eth = terminal voltage = 1.5v

With 0.1A flowing, the pd across Rth = 1.50 - 1.48 = 0.02 v

Rth  = V / I = 0.02 / 0.1 = 0.2 ohms

With the terminals shorted all  of Eth will be across Rth

Isc = 1.5 / 0.2 = 7.5 A

Terminal voltage = 0.