A) 50
B) 100
C) 150
D) 200
Correct Answer: B
Solution :
Let \[{{r}_{1}}\] be the radius of porcelein cylinder and\[N\]be the number of turns required, then \[l=2\pi {{r}_{1}}N\] Let \[{{r}_{2}}\] be the radius of wire, then \[A=\pi {{r}_{2}}^{2}\] We know, \[R=\rho \frac{l}{A}=\rho \frac{2{{\pi }_{1}}N}{\pi {{r}_{2}}^{2}}\] \[\therefore \] \[N=\frac{R{{r}_{2}}^{2}}{2\rho {{r}_{1}}}=\frac{20\times {{(0.5\times {{10}^{-3}})}^{2}}}{2\times {{10}^{-6}}\times (2.5\times {{10}^{-2}})}=100\]
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