A sheet of charge lies flat (horizontal) on a tabletop, and a point charge is fi

Question

A sheet of charge lies flat (horizontal) on a tabletop, and a point charge is fixed in place floating 4 cm above the sheet of charge. The sheet of charge is 1 m by 1 m -- large enough that it can be treated as an infinite sheet -- and has a total charge of +7 C. The point charge has a value of +7 C.

What direction is the net electric field at a point halfway between the point charge and the sheet of charge? If the net electric field at this point is 0, select "No direction -- zero electric field". 1---Select---2UpDownNo direction -- zero electric field

Explain your reasoning, but without referring to any calculations of the electric field.

2

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Explanation / Answer

(1)

Electric field at halfway b/w point charge and sheet of charge,

Since the charge is positively charged so, elecric field due to point charge is downward.

elecric field due to sheet (+vely charged) is upward.

As the electric field due to point charge is more strong so direction of net electric field will be downwards.

(2)

Given that,

distance of point charge, d = 4 cm = 0.04 m

area of sheet, A = 1 * 1 = 1 m^2

elecric field due to point charge at the halfway point-

E1 = kq / (d/2)^2

E1 = 9*10^9*7*10^(-6) / (0.02)^2

E1 = 15.75*10^7 N/C (downward)

elecric field due to sheet of charge at the halfway point-

E2 = q / 2Ae0

E2 = 7*10^(-6) / 2*1*8.85*10^(-12)

E2 = 0.395*10^6 (upward)

Net electric field at halfway point,

E = E1 - E2

E = 1.57*10^8 N/C (downwards)

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