A) \[5\,\Omega \]
B) \[1\,\Omega \]
C) \[7\,\Omega \]
D) \[3\,\Omega \]
Correct Answer: B
Solution :
As \[I=\frac{\varepsilon }{R+r}\] In first case, \[I=0.5\,A;\,R=12\Omega \] \[0.5=\frac{\varepsilon }{12+r}\Rightarrow \varepsilon =6.0+0.5\,r\] (i) In second case, \[I\text{ }=\text{ }0.25\text{ }A;\text{ }R\text{ }=\text{ }25\text{ }\Omega \] \[\varepsilon =6.25+0.25\,r\] (ii) From equation (i) and (ii), \[r=1\Omega \]
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