a) R2 si R3 in paralel
[tex] \frac{1}{r2} + \frac{1}{r3} = \frac{1}{rp} [/tex]
[tex] \frac{1}{40} + \frac{1}{10} = \frac{5}{40} [/tex]
5Rp=40 => Rp=8
Rp si R1 in serie Rp+R1=8+20 =28
Re=28
b) I(R+r)=E
I(28+2)=30
I×30=30 => I= 1A
c) U=R1×I
U=20 V
P1=U×I
P1=20×1 =20 W
