A) 5 cm
B) 25 cm
C) 10 cm
D) 20 cm
Correct Answer: C
Solution :
\[\frac{{{B}_{1}}}{{{B}_{2}}}=\frac{{{d}_{1}}}{{{d}_{2}}}{{\left( \frac{d_{2}^{2}-{{l}^{2}}}{d_{1}^{2}-{{l}^{2}}} \right)}^{2}}\Rightarrow \frac{12.5}{1}=\frac{10}{20}{{\left( \frac{400-{{l}^{2}}}{100-{{l}^{2}}} \right)}^{2}}\] \[\Rightarrow l=5\ cm\] Hence length of magnet \[=2l=10\ cm\]You need to login to perform this action.
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