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(b) Two resistors, when connected in series have total resistance of 25 ohms. If they areconnected in parallel the value goes down to 6 ohms. Find their values. |
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Answer» Answer: The total resistance of resistors in series is equal to the sum of their individual resistances. That is, R total =R 1 +R +R 3 . The total resistance will always be less than the value of the SMALLEST resistance That is, R total
1 = R 1
1 + R 2
1 + R 3
1 thatis,R=R total
−1 . In this case, the total resistance of the resistors CONNECTED in series is given as R 1 +R 2 =45 - eqn 1 The total resistance of the resistors connected in parallel is given as R 1
1 + R 2
1 = 10 1 thatis, R 1
1 + R 2
1 =0.1 - eqn 2 Putting the value of R 1 +R 2 in eqn 2, we get, R 1 R 2 =10×45=450ohms. Now, From the identity, (R 1 −R 2 ) 2 =(R 1 +R 2 ) 2 −4R 1 R 2 ,weget,R 1 −R 2 =15ohms - eqn 3. Adding eqn 2 and eqn 3, 1 =60ohmsThatis,R 1 =30ohms. Substituting this value in eqn 3, we get, R 2 =(30−15)=15ohms. Hence, the values of the resistors are 30 OHMS and 15 ohms
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