Question

n the figure two large, thin metal plates are parallel and close to each other. On their inner faces, the plates have excess surface charge densities of opposite signs and magnitude 7.52

Answer 1

Wow! 7.52*10^-22 C/m^2 is an extremely small charge! Taking into account that the charge of an electron is approximately 1.6*10^(-19) C, the charge density you list would mean that on average there is only one excess electron per 320 m^2 on the negatively charged plate! This hardly warrants using the continuum approximation below (one would need to assume the electron charge is quantum mechanically delocalized uniformly over the plate ), but I will approach the problem along that classical line anyway...

Hence in betweeen the plates,

E = -?/2e0 - ?/2e0 = -?/e0

= 7.5*10^-22 / 8.85*10^-12 = 0.85*10^-10

The electric field of an infinite plane charge density is independent from the distance (E = sigma/eps0).
Because the charge densities on the plates are equal in magnitude but of opposite charge, there is no net field outside the plates. Between the plates the field lines point from the positive charge density to the negative charge density, hence horizontally to the left (c. 4)

Note that because there is no E field outside the plates, there is no determined direction (what would be the direction of a vector of zero length...?) Hence outside the plates the most appropriate answer listed in (a) and (b) would be 6. Undetermined.

Answer 2

The surface charge density of the plates 7.0x1022 Clm2 (a) The electric field to the left of the plates 24 2局 Theelectric field duetolet plateistowardsrightside whereas due to right plate is towardslef side of equal magnitudes because of samech arg e density (b)The electric field to the rigth of the plates 2ら 2ら (c)In betweew the plates σσ Here the electric field due to negtive plate towards left and due to positive plate towards eft so 70x10 2(8.85x10"