--schakelaar open--
P2 = 25 Watt     want R1=R2
Pt = 2x25 = 50 Watt
P = UxI  >>>   It= P/U 50/100 = 0.5 A
U = IxR  >>>   Rt= U/I 100/0.5 =200 Ohm
R1 = 100 Ohm en R2 = 100 Ohm
Ur = IrxR     0.5x100= 50 V

---schakelaar gesloten---
R1 vervalt , wordt kortgesloten
I = U/R 100/100 = 1 A
P = UxI 100x1 = 100 Watt
Ur2 = IR2xR2 = 1x100 =100 V

001

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007 P = U x I