One is with a 10MΩ FET analog meter for measuring the voltage across a smoke precipitator ... in case some of the resistors shorted. The calculations for that are very involved so I won ...

A LED takes a current of \(12.5 mA\) when the voltage across it is 2 V. Draw a suitable circuit and calculate the value of the series resistor needed to operate the LED from a \(9 V\) battery.