1.
ε=6, C=1200 пФ=1200*10^-12Ф, S=1,2*10^-3 м³. d-?
C=ε0εS/d, d=ε0εS/C.
d=8,85*10^-12*6*1,2*10^-3/(1200*10^-12) = 0,053*10^-3 м = 5,3*10^-5 м.
2.
r1=0,2 м, F1=F2, ε1=2, ε2=1. r2-?
F1=kq1q2/(ε1r1²), F2=kq1q2/(ε2r2²),
kq1q2/(ε1r1²)=kq1q2/(ε2r2²),
1/(ε1r1²)=1/(ε2r2²),
ε1r1²=ε2r2²,
r2²=ε1r1²/ε2.
r2=√(ε1r1²/ε2)=r1√ε1/ε2.
r2=0,2√(2/1)= 0,28 м.