# Three identical metal plates with large surface areas are kept parallel to each other.The leftmost plate is given a charge Q, the rightmost is given a charge -2Q & the middle one remains neutral.Find the charge appearing on the outer surface of the rightmost plate.      { plzz  let me know how to you take the sign meaning + or - for the electric field due to each surface of the plate}

Arun Kumar IIT Delhi
8 years ago
Let's say three plates charges Q1,Q2,Q3
We find equations by assuming electric field in the conductor zero.
Charges are conserved on each plate.
$Q_{a,left}=Q_{c,right}\\ Q_{a,right}+Q_{b,left}=0\\ Q_{b,right}+Q_{c,left}=0\\ Q_{a,left}+Q_{a,right}=Q1 \\Q_{b,left}+Q_{b,right}=Q2 \\Q_{c,left}+Q_{c,right}=Q3 \\adding\,all=>Q_{a,left}=(Q1+Q2+Q3)/2=Q_{c,right}=-Q/2 \\=>Q_{c,left}=Q3-Q_{c,right}=(Q3-Q2-Q1)/2=-3Q/2 \\=>Q_{b,right}=-Q_{b,left}=3Q/2 \\=>Q_{a,right}=-3Q/2$
Thanks & Regards
Arun Kumar
IIT Delhi
NDACE
11 Points
6 years ago
GOOD effort.