A) 2 : 1
B) 4 : 1
C) 3 : 1
D) 1 : 4
Correct Answer: C
Solution :
In stretching \[R\propto {{l}^{2}}\] Þ \[\frac{{{R}_{2}}}{{{R}_{1}}}=\frac{{{l}_{2}}^{2}}{{{l}_{1}}^{2}}\]Þ \[\frac{{{R}_{2}}}{{{R}_{1}}}={{\left( \frac{2}{1} \right)}^{2}}\] Þ\[{{R}_{2}}=4{{R}_{1}}\]. Change in resistance \[={{R}_{2}}-{{R}_{1}}=3{{R}_{1}}\] Now, \[\frac{\text{Change}\,\,\text{in}\,\,\text{resistance}}{\text{Original}\,\,\text{resistance}}=\frac{3{{R}_{1}}}{{{R}_{1}}}=\frac{3}{1}\]
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