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Potential due to a Group of Point Charges

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Estimated time: 6 minutes
CISCE: Class 12

Introduction

Electric potential at a point describes the work done per unit positive charge in bringing it from infinity to that point, without any acceleration. Since potential is a scalar quantity, the total potential due to several charges is found by simple algebraic addition — unlike the electric field, which requires vector addition.

CISCE: Class 12

Potential Due to a Group of Point Charges

Discrete System of Charges

For charges +q1, +q2, −q3, −q4​ at distances r1, r2, r3, r4​ from point P, the resultant potential is:

V = \[\frac{1}{4\pi\varepsilon_0}\left(\frac{q_1}{r_1}+\frac{q_2}{r_2}-\frac{q_3}{r_3}-\frac{q_4}{r_4}\right)\]

For n point charges, generalized as:

V = \[\frac{1}{4\pi\varepsilon_0}\sum_{i=1}^n\frac{q_i}{r_i}\]
where ri​ is the distance of the i-th charge from point P (NOT the distance between charges).
Sign Convention:
  • Potential due to a positive charge is positive.
  • Potential due to a negative charge is negative.
  • Net potential can be zero even when charges are non-zero, if positive and negative contributions cancel.
CISCE: Class 12

Continuous Charge Distributions

When charge is spread continuously, the sum becomes an integral over infinitesimal charge elements dq:

V = \[\frac{1}{4\pi\varepsilon_0}\int\frac{dq}{r}\]

Types of Continuous Distributions

Distribution Type Charge Element Formula
Surface Charge dq = σ dA V = \[\frac{1}{4\pi\varepsilon_0}\int_A\frac{\sigma dA}{r}\]
Volume Charge dq = ρ dV V = \[\frac{1}{4\pi\varepsilon_0}\int_V\frac{\rho dV}{r}\]

Here σ is surface charge density and ρ is volume charge density

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Electrostatic Potential part 9 (Potential Difference due to system of charge) [00:03:18]
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