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1. Electric Charges and Fields
hard
For given arrangement, where four charge fixed at ends of as quare as given, find value of additional charge $Q$ to be put on one of the vertices so that component of net electric field along the vertical symmetric axis is zero at every point on the vertical

A
$-q$
B
$-3q$
C
$-5q$
D
$-4q$
Solution
For zero electric field compment along axis
$\frac{\mathrm{k}(4 \mathrm{q}) \mathrm{h}}{\left(\frac{\mathrm{a}^{2}}{2}+\mathrm{h}^{2}\right)^{3 / 2}}=\frac{\mathrm{K}(\mathrm{Q})}{\left(\frac{\mathrm{a}^{2}}{2}+\mathrm{h}^{2}\right)^{3 / 2}}$
$Q=4 q$
$Q=4 q$ (with, negative sign)
Standard 12
Physics