A) -9e
B) -7e
C) -5e
D) -3e
Correct Answer: C
Solution :
The given, \[r=1.64\mu m=1.64\times {{10}^{-6}}m\], \[\rho =0.85\times {{10}^{3}}kg/{{m}^{3}},E=1.9\times {{10}^{5}}N/C\] and \[g=9.8\,m/{{s}^{2}}\] \[\because \] \[E=\frac{f}{q}\Rightarrow E=\frac{mg}{q}\] \[m=\frac{4}{3}\pi {{r}^{3}}.\,\rho \] \[q=\frac{mg}{E}\] \[q=\frac{\frac{4}{3}\pi {{r}^{3}}.\,\rho \,.\,g}{E}\] \[q=\frac{4\times 3.14\times {{(1.64\times {{10}^{-6}})}^{3}}\times 0.85\times {{10}^{3}}\times 9.8}{3\times 1.9\times {{10}^{5}}}\] \[q=\frac{461.49\times {{10}^{-20}}}{5.7}C\] \[q=-\frac{461.49\times {{10}^{-20}}}{5.7\times 1.6\times {{10}^{-19}}}e\] \[q=-\frac{461.49\times {{10}^{-1}}}{9.12}e\] \[=-50.6\times {{10}^{-1}}e=-5.0\,e=-5\,e\]
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