Bài 1:
a, $F=k.\dfrac{|q_{1}.q_{2}|}{MN²}=9.10^{9}.\dfrac{3.10^{-8}.4.10^{-8}}{0,05²}=4,32.10^{-3}N$
b, Ta có: $\vec{E_{1}}↑↑\vec{E_{2}}$
$⇒E=E_{1}+E_{2}=k.\dfrac{|q_{1}|}{OM²}+k.\dfrac{|q_{2}|}{ON²}$
$=9.10^{9}.\dfrac{3.10^{-8}}{0,01²}+9.10^{9}.\dfrac{4.10^{-8}}{0,04²}$
$=2925000V/m$
Bài 2:
a, $E_{CD}=\dfrac{U_{CD}}{d_{CD}}=\dfrac{100}{0,04}=2500V/m$
$U_{AB}=0$
$U_{BC}=E.d_{BC}=2500.AB=200V$
b, $A_{BC}=e.U_{BC}=1,6.10^{-19}.200=3,2.10^{-17}J$
$A_{BD}=e.U_{CD}=1,6.10^{19}.100=1,6.10^{-17}J$
