Cracking the SAT Physics Subject Test

potential at A due to Q 2 alone (ignoring the presence of Q 1 ) is

ΦA2 = k Q 2 /rA2 = (9 × 10^9 )(−5 × 10−9)/(5 × 10−2) = −900 V

Therefore, the total electric potential at Point A, due to both source charges, is

ΦA = ΦA1 + ΦA2 = (3000 V) + (−900 V) = 2100 V

Similarly, the total electric potential at Point B is

Summary of Equations so Far

We’ve learned a lot of equations up to this point. Let’s put some relations behind
them: