Physics

Problem

A battery rated

9\,\text{V},\;3000\,\text{mAh}

powers a gadget that draws a steady current of

300\,\text{mA}

. Which one of the following changes will approximately double the operating time on a single charge? a) Decreasing the gadget current to

200\,\text{mA}

while using the same battery b) Connecting two identical

9\,\text{V},\;3000\,\text{mAh}

batteries in series to obtain an

18\,\text{V}

supply at

300\,\text{mA}

c) Replacing the battery with one rated

9\,\text{V},\;6000\,\text{mAh}

while keeping the current

300\,\text{mA}

d) Replacing the battery with one rated

12\,\text{V},\;3000\,\text{mAh}

while keeping the current

300\,\text{mA}