Multiple-Choice Homework Problem 2.8 Two infinite planes of charge are drawn to

Question

Multiple-Choice Homework Problem 2.8 Two infinite planes of charge are drawn to the right. One infinite uniform plane of charge occupies the r y plane with charge density, orzy 3.0 C/ Another infinite uniform plane of charge occupies the y-2 plane with charge dens 2.0 C/ Compute the electric field at io (1.0cm, 0, 1.0cm). Select One of the Following: (a) -2.8 x 5 N 10 (b) -1.0 x 10s 3.1 x 103 3N (c) 1.1 x 105 1.7 x 10 5 N (d) 6.0 x 104 (e) -1.1 x 100 N 1.7 x 103 Multiple-Choice Homework Problem 2.9 A +2nC point charge is at the point (-1cm. 2cm, 3cm). Compute the electric field at a point P at (-2cm, -6cm,2cm). Select One of the Following: (a) (-2.4 x 10s 9.4 x 10 2.4 x 103 3N (b) (-2.4 x 105 9.4 x 5N 2.4 x 105 10 (c) (2.4 x 3N 9.4 x 10 2.4 x 10 C) 103 3N (d) (2.4 x 10 N 9.4 x 10 2.4 x 105 5 5N (e) (-2.4 x 10 9.4 x 104 2.4 x 104 4N 4N

Explanation / Answer

problem 2.8:
as we know, for an infinite plane charge with charge density pho,
then electric field magnitude is given by pho/(2*epsilon)

direction of the field will be radially away from the plane of charge if charge is positive and towards it ,

if the charge is negative.

for the charge in y- z axis:
magnitude of electric field=1.13*10^5 N/C

as the charge is negative, the direction will be towards -ve x axis.

for the charge in x-y plane:
magnitude of electric field=1.6949*10^5 N/C

and as the charge is positive, the direction will be along +ve z axis.

hence rounding off all the magnitudes and using unit vector notation,

electric field=-1.1*10^5 x + 1.7*10^5 z

hence the correct answer will be option E.

problem 2.9:
as the charge is positive, the direction of electric field will be from the charge and towards the point P.

then the vector in this direction=(-1,-2,3)-(-2,-6,2)=(1,4,1)

distance between the charge and the point=sqrt(1^2+4^2+1^2)=4.242 cm

unit vector along this direction=(1,4,1)/4.242 =(0.2357,0.943, 0.2357)

magntiude of the electric field=9*10^9*charge /distance^2=10003.021 N/C

hence multiplying with the unit vector, we get the complete expression as

(2357.71,9432.84,2357.71) N/C

hence, after rounding off, the correct answer is option C

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