Question

The side of an equilateral triangle is 20 cm. Two equal point chargers (+) 3 nC are placed at its two corners. What will be the amount of work done in bringing a (+) nC test charge from infinity to third corner of the triangle.? (1 mark for formula, 1 mark for calculation).​

Answer 1

We know that work done = potential ×  charge

Let  ABC  be the equilateral triangle

Let  +3nC  charges are placed on corners of  A  and  B  

Let we have to bring  +1nC  charge from infinity to points  C  

to find potential at  C  

potential at  C=  potential due to  A  + potential due to  B  

=kqAAC+kqBBC  

but  qA=qB=+3nC  

and  AC=BC=20cm=0.2m  

∴  potential at  C=k×3nC0.2+k×3nC0.2  

=9×1092×3×10−92×10−1  

=54×1012  

=270V  

∵  Work done=potential × charge

∴  Work done =

W=270×1nC  

=270×10−9J  

=2.7×10−7J: