a) Rtđ = 600 + 2000 = 2600 ôm

I = 100 / 2600 = 1/26 A

b) Rtđ = 1000 ôm

I = 100 / 1000 = 0,1 A

a) 4 cách:

R nt R nt R => Rtđ 1: 3R

R nt (R //R) => Rtđ 2: 3R/2

R // (R nt R) => Rtđ 3: 2R/3

R // R // R => Rtđ 4: R/3

=> R/3 < 2R/3 < 3R/2 < 3R

=> Rtđ 4 < Rtđ 3 < Rtđ 2 < Rtđ 1

=> I4 > I3 > I2 > I1

=> I1 = 0,3 A

=> U = I1 . Rtđ 1 = 0,3 . 3R = 0,9R

=> I2 = U/Rtđ 2 = 0,9R / (3R/2) = 0,6 A

=> I3 = U/Rtđ 3 = 0,9R / (2R/3) = 1,35 A

=> I4 = U/Rtđ 4 = 0,9R / (R/3) = 2,7 A

a) Rtđ = 70 + 50 = 120 ôm

U = Rtđ . I = 120 . 0,5 = 240 V

b) U1 = I . R1 = 0,5 . 70 = 35 V

U2 = I . R2 = 0,5 . 50 = 25 V

c) P1 = U1 . I = 35 . 0,5 = 17,5 W

P2 = U2 . I = 25 . 0,5 = 12,5 W

Vì U ko đổi, I1 < I2 ( 4A < 6A )

=> R1 > R2

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