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i have the correct answers and equations, i just am not ending up with those ans

ID: 1699108 • Letter: I

Question

i have the correct answers and equations, i just am not ending up with those answers.....
Two parallel plates have dimension of 25cm x 36cm, adn they each have voltage of 75V applied across them
a)if the plate separation is 4mm, what is the electric field between the plates?
***E=18,750V/m
b)what is the surface charge density on each of teh plates?
***1.66(10^7)C/m^2
c)what is total charge on each plate?
***Q=.015
d)if a proton is released from the positive plate, what speed will it acquire when it hits the negative plate.
***v=2(10^5)m/s

Explanation / Answer

Given

area of plates A = 0.25*0.36 m^2   = 0.09 m^2

potential across the plates   V = 75 V

a) the distance between the plates d = 4*10^-3 m

    Electric field between the plates   E = V / d  

                                                               = 75 / 4*10^ -3

                                                               =    18750 V / m

b) surface charge density on each plate

                  = E _o

                         = 18750 * 8.85*10^ -12 = 1.659*10^ -7 C / m^2

c) charge on each plate

                Q = A

                     = 1.659 *1^ -7   * 0.09 = 0.149 *10^ - 7 C

d)   1 / 2 m v^2    = V q

        1 / 2 ( 1.6*10^ -27 ) v^2   = 75 *1.6*10^ -19

                 v^2   = 150*10^ 8

                    v = 12.24*10^ 4

                       = 1.224 *10^ 5 m/s