Question Details

Two large plane parallel sheets shown in the figure have equal but opposite surface charge densities +σ and–σ. A point charge q placed at points P1, P2, and P3 experiences forces F1, F2, and F3 respectively. Then,



Choose the correct answer from the options given below.

Options

A

F1 =0, F2 =0, F3 =0

B

F1=0,F20,F3=0

C

F10,F20,F30

D

F1=0,F30,F2=0

Show Answer

Correct Answer :

Option B

F1=0,F20,F3=0

Solution :

The correct answer is:
F 1 = 0 , F 2 0 , F 3 = 0

Step-by-Step Explanation:

1. Understanding the Setup from the Image:
The provided image shows two large, vertical, parallel plane sheets:
- The left sheet has a uniform positive surface charge density of +σ.
- The right sheet has a uniform negative surface charge density of -σ.
Three distinct points are marked:
- P1: located in the region to the left of the positive sheet.
- P2: located in the region between the two parallel sheets.
- P3: located in the region to the right of the negative sheet.
At each of these points, a test point charge q is placed, experiencing forces F1, F2, and F3 respectively.

2. Electric Field due to an Infinite Plane Sheet of Charge:
According to Gauss's Law, the magnitude of the electric field E produced by an infinite, non-conducting plane sheet of uniform surface charge density σ at any nearby point is constant (independent of the distance from the sheet) and is given by:
E = σ 2 ε 0
The direction of this electric field is:
- Directed perpendicularly away from the sheet if the charge is positive (+σ).
- Directed perpendicularly towards the sheet if the charge is negative (-σ).

3. Calculating the Net Electric Field and Force at Each Point:

At Point P1 (Left Region):
- The electric field due to the positive sheet (E+) points to the left (away from it).
- The electric field due to the negative sheet (E-) points to the right (towards it).
Since the magnitudes are equal:
E 1 = E + - E - = σ 2 ε 0 - σ 2 ε 0 = 0
Therefore, the force experienced by the charge q at P1 is:
F 1 = q E 1 = 0

At Point P2 (Middle Region):
- The electric field due to the positive sheet (E+) points to the right (away from it).
- The electric field due to the negative sheet (E-) also points to the right (towards it).
Since both fields point in the same direction, they reinforce each other:
E 2 = E + + E - = σ 2 ε 0 + σ 2 ε 0 = σ ε 0 0
Therefore, the force experienced by the charge q at P2 is non-zero:
F 2 = q E 2 = q σ ε 0 0

At Point P3 (Right Region):
- The electric field due to the positive sheet (E+) points to the right (away from it).
- The electric field due to the negative sheet (E-) points to the left (towards it).
Since the magnitudes are equal and opposite:
E 3 = E + - E - = σ 2 ε 0 - σ 2 ε 0 = 0
Therefore, the force experienced by the charge q at P3 is:
F 3 = q E 3 = 0

4. Summary of Results:
- At P1: F1=0
- At P2: F20
- At P3: F3=0
This perfectly matches the correct option.

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