Question

+q, +2q, +3q, +4q, ……(up to +20q) charges are situated at coordinates (0,0) , (1,0) ,(2,0) , ….. (Up to 20). What is the total charge stored in the system?

(a) +20q

(b) +210q

(c) +420q

(d) +190q

The question was posed to me during an online exam.

This is a very interesting question from Basic Properties of Electric Charge in section Charges and Fields of Physics – Class 12

Answer 1

Right option is (b) +210q

For explanation I would say: As charge is additive, total charge will be (1+2+3+4+…. +20)*q=\(\frac{20*21}{2}\)*q= 210q. But if the polarities of the charges are different i.e. some of them are positive and some are negative, then the result will be different. We have to add separately the positive charges and the negative charges.