12.39: For the circuit shown, all wires have no resistance,
cf0ab5 hl/ n-a,4mb;ro4eow othe battery has a constan
b- ,4fo5/laoanco4bw; e0m hrt internal resistance of $r = 8.0Ω$ and the two lightbulbs (#1 and #2) are identical, each with resistance R bulb. The variable resistor is initially setto $R = 26.0Ω$ . The switch in the circuit now is closed. To what resistance must the variable resistor be set if bulb #1 is to have the same brightness after the switch is closed as it did with the switch open?