Six lead-acid type of secondary cells each of emf `2.0` V and internal resistance `0.015Omega` are jouned in series to provide a supply to a resistance of `8.5Omega`. What are the current drawn from the supply and its terminal voltage ?
(b) A secondary cells after long use has an emf of `1-9` V and a large internal resistance of `380 Omega`. What maximum current can be drawn from the cell ? Could the cell drive the starting motor of a car ?

Explanation

Six cells are joined in series.

Equivalent emf is `2xx6=12V`
Equivalent internal resistance is `0.015xx6=0.09Omega`
Current drawn from the battery
`I=(12)/(8.5+0.09)=(12)/(8.59)=1.4A`
Terminal voltage of the battery
`V=epsilon-Ir=12-1.4xx0.09`
`V=12-0.126=11.87V`
(b) Maximum current is drawn from a battery when external resistance is treated to be zero.
`I_(max)=(1.9)/(380)=0.005A`.
To start a car a current of the order of 100 A is needed, so the battery mentioned above can not drive the starting motor of a car.