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1. Electric Charges and Fields
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$ABC$ is a right angled triangle in which $AB = 3\,cm$ and $BC = 4\,cm$. And $\angle ABC = \pi /2$. The three charges $ + 15,\; + 12$ and $ - 20\,e.s.u.$ are placed respectively on $A$, $B$ and $C$. The force acting on $B$ is.......$dynes$
A
$125$
B
$35$
C
$25$
D
$0$
Solution
(c) Net force on $B$ ${F_{net}} = \sqrt {F_A^2 + F_C^2} $
${F_A} = \frac{{15 \times 12}}{{{{\left( 3 \right)}^2}}} = 20\,\,dyne$, ${F_C} = \frac{{12 \times 20}}{{{{\left( 4 \right)}^2}}} = 15\,\,dyne$
$==>$ ${F_{net}} = \sqrt {F_A^2 + F_C^2} = \sqrt {{{(20)}^2} + {{(15)}^2}} = 25\,\,dyne$
Standard 12
Physics
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