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A resistance network is connected to a battery as shown in the figure below. If the intrrnal resistance of the battery is 5omega, then the value of R (in omega) for maximum power delivered to the network is

Answer»

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Solution :Given is an unbalanced Wheatstones. bridge, in which current distribution will be as SHOWN
Now in loop ABCA, USING KVL we have,
`- 3Ri_(1)-4R(i_(1)-i_(2))+ 2Ri_(2)= 0`
`- 3Ri_(1)-4Ri_(i)+4Ri_(2) + 2Ri_(2)=0`
`7i_(1)=6i_(2)`
`rArr i_(1)=(6)/(7)i_(2)`
Also,`i_(1)+ i_(2)=i`
Hence, `((6)/(7)+1)i_(2)=i or i_(2)=(7)/(13)i`
`therefore i_(1)=(6)/(7)i_(2)=(6)/(7)XX(7)/(13)i rArr i_(1)= (6)/(13)i`
Now from loop ABDA (which includes cell ), we have, `3Ri_(1) +2Ri_(2) = V` (nearly because internal resistance in not taken in ACCOUNT)
`3Rxx(6)/(13)i+2Rxx(7)/(13)i=iR_(ed)`
`rArr R_(eq)= R ((18 +14)/(13))=(32)/(13)R`
For maximum power delivered to circuit, (internal resistancenof source )= external resistance)
`rArr 5 = (32R)/(13) or R=(13xx5)/(32)=203 Omega`
or `R = 2 Omega`


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