A) \[2.0\,\Omega \]
B) \[1.5\,\Omega \]
C) \[1.0\,\Omega \]
D) \[0.5\,\Omega \]
Correct Answer: D
Solution :
(d) \[0.5\,\Omega \] Current drawn from the cell, \[l=\frac{\varepsilon }{R+r}\] \[0.9=\frac{\varepsilon }{2+r}\] Or \[\varepsilon =0.9\,(2+r)\] (1) Similarly, \[0.3=\frac{\varepsilon }{7+r}\] Or \[\varepsilon =0.3\,(7+r)\] (2) From eqs. (1) and (2), we get \[0.9(2+r)=0.3(7+r)\] \[3(2+r)=7+r\] \[\Rightarrow ~6+3r=7+r~\] \[\Rightarrow ~2r=1~\] or \[r=0.5\,\Omega \]
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