Hi, I have been trying to solve 2 questions of same type but I don\'t know how t

Question

Hi,

I have been trying to solve 2 questions of same type but I don't know how to find R1 when there is no Requivalent is not given.

I have attached the picture, sorry when I uploaded on chegg the picture is too big.

Question 7-6

http://imageshack.us/a/img145/89/82501777.jpg

Circuit Diagram for question 7-6

http://imageshack.us/photo/my-images/203/71040323.jpg/

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Question 7-31 with circuit diagram

http://imageshack.us/a/img580/439/96911494.jpg

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Please can someone show me how to solve these 2 questions.

Thank you

Explanation / Answer

This qs can be solves by simple series parallel techniques Not necessary to go for KVL (A) Fig 7.18 R1is unknown R5 &R4 are parallel R54 = R5*R4(R5+R4) = 211.630 ohm R54,R2 &R3 are in series R1net = R54+R2 + R3 = 120+230 + 211.630 ohm R1net =>561.63 ohm R1net & R1 are parallel Rnet = R1net*R1/(R1net + R1) Req = Rnet = V/I = 50/(0.2) = 100 ohm 100 = 561.3*R1/(561.3 + R1) =>56130 + 100R1 = 561.3R1 =>R1 = 121.68 ohms (B) Fig 7.31 R2 is unknown R2&R1 are in parallel R21 = R2*R1/(R2+R1) = 29*R2/(29+R2) R4,R5,R6 are in series R1net = R4 + R5 + R6 = 16 + 11 +5 = 32 kiloohm R1net is in parallel with R3 R2net = 15.75 kiloohm Rnet = R1net + R21 (They are in series) Req = Rnet = V/I = 29761.90 = 29.762 kilo ohm R21 = Rnet - R1net = 29.762 - 15.75 = 14.1 kilo ohm R21 = 29*R2/(29+R2)= 14.1 =>29*R2 = 408.9 +14.1*R2 R2 = 408.9/(29-14.1) = >27.44 kilo ohm

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