1.

B. When two resistors are connectedin series, their effective resistanceis 80 12. When they are connectedin parallel, their effective resistanceis 20 92. What are the values of thetwo resistances?

Answer»

In series, R1 + R2 = 80in parallel, 1/R1 + 1/R2=1/20R1+R2/R1R2 = 1/2080/R1.R2 = 1/20R1.R2 = 1600put R2=80-R1R1(80-R1)=160080R1-R1^2 = 1600R1^2 - 80R1 + 1600=0R1^2 - 40R1- 40R1 + 1600=0R1(R1-40)-40(R1-40)=0(R1-40)(R1-40)=0R1=40 R2=80

R2=80-R1=80-40=40 ohm



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