Hello, hello? My phone's almost dead...drat.

Electricity and Magnetism Level 2

Cell phone batteries are rated by their voltage and total ability to output current, usually in units of milliamperes \(\times\) hours, for which we use the abbreviation mA-h. If a battery has a value of \(1000~\mbox{mA-h}\), this means it can deliver \(1000~\mbox{mA}\) of current for one hour. The cell phone battery in this question has a voltage rating of \(3.7~\mbox{V}\) and current rating of \(1100~\mbox{mA-h}\). How much energy in Joules does the battery store when fully charged?

Details and assumptions

  • Assume the voltage remains constant as the battery discharges. The voltage of real batteries decreases as they discharge, but we'll ignore that effect for simplicity.
  • Hint: Try converting the rating to Amp-seconds and think how you could use that unit with Volts to get an energy.

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