A) \[0.85\times {{10}^{7}}m{{s}^{-1}}\]
B) \[\text{1}.0\times \text{l}{{0}^{\text{7}}}\text{ m}{{\text{s}}^{\text{-1}}}\]
C) \[\text{1}.\text{25}\times \text{l}{{0}^{\text{7}}}\text{ m}{{\text{s}}^{\text{-1}}}\]
D) \[\text{1}.\text{65}\times \text{l}{{0}^{\text{7}}}\text{ m}{{\text{s}}^{-1}}\]
Correct Answer: A
Solution :
Given, \[E={{10}^{4}}N{{C}^{-1}}\], \[s=2\times {{10}^{-2}}m\] U = 0 The force acting on the electron = eE Acceleration of electron \[=\frac{eE}{m}\] Now, as \[{{v}^{2}}={{u}^{2}}+2as\] \[{{v}^{2}}=2\times \frac{eE}{m}\times \,s\] \[=2\times [1.76\times {{10}^{11}}\times {{10}^{4}}\times 2\times {{10}^{-2}}]\] \[\left[ \frac{e}{{{m}^{.}}}=1.76\times {{10}^{11}}C\,k{{g}^{-1}} \right]\] \[=7.04\times {{10}^{13}}\] \[\Rightarrow \,\,v=0.85\times {{10}^{7}}m{{s}^{-1}}\]
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