Question

The emf of a flashlight battery is roughly constant with time, but its internal resistance increases with age and use. What sort of meter should be used to test the freshness of a battery?

Short answer

An ohmmeter is used to test the freshness of a battery.

Step-by-step solution

Determining the type of meter

An Ohmmeter is used to directly test the battery's internal resistance.

If the short circuit current is measured with an ammeter, the internal resistance may be computed using Ohm's law using the measured current and the battery's electromotive force ($\epsilon$).

$r=\frac{s}{l_{sc}}$

Hence, an Ohmmeter is used to test the freshness of a battery.