A) \[3\times {{10}^{4}}V{{m}^{-1}}~\]
B) \[3\times {{10}^{6}}V{{m}^{-1}}\]
C) \[3\times {{10}^{-4}}V{{m}^{-1}}\]
D) \[3V{{m}^{-1}}\]
Correct Answer: A
Solution :
: Here, \[Q=3\text{ }nC=3\times {{10}^{-9}}C\] \[R=2cm=2\times {{10}^{-2}}m\] At a point 3 cm from the centre, i.e., \[r=3cm=3\times {{10}^{-2}}m\] \[\therefore \] Electric field, \[E=\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{Q}{{{r}^{2}}}=\frac{9\times {{10}^{9}}\times 3\times {{10}^{-9}}}{{{(3\times {{10}^{-2}})}^{2}}}\] \[=3\times {{10}^{4}}\,V\,{{m}^{-1}}\]
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