Two identical thin metal plates has charge q 1 and q 2 respectively such that q 1 > q 2 . The plates…

Two identical thin metal plates has charge q1 and q2 respectively such that q1>q2. The plates were brought close to each other to form a parallel plate capacitor of capacitance C. The potential difference between them is :
  1. q1+q2C
  2. q1-q2C
  3. q1-q22C
  4. 2q1-q2C

Solution

On bringing the charged metal plates closer, electric field E in the intervening space is E=E1+E2

Where

Intensity of field due plate charged by q1 is E1 =σ12ε0 = q12ε0A(directed rightwards)

And Intensity of field due to plate charged by q2 is 

E2 =σ22ε0 = q22ε0A (directed leftwards)
So, Net field is given by 

E=E1+E2  E = E1- E2

 E =q12ε0A-q22ε0A=q1-q22ε0A   ...1

For parallel plate capacitor C = ε0Ad   ...2

From above two equations 

E=q1-q22Cd   ...3 

 Relation between intensity of field E and potential difference V between the plates is 

E = Vd   ...4

From equation 3 and 4

V = q1-q22C

Asked in: JEE Main 2022 (29 Jul Shift 2)

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