Electrostatic Potential and Capacitance – Class 12 Physics Notes
๐งฒ Electrostatic Potential and Capacitance – Class 12 Physics Notes
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๐น Introduction
This chapter deals with electric potential, potential energy, equipotential surfaces, and capacitors.
It is a continuation of Chapter 1 (Electric Charges and Fields).
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⚡ Electrostatic Potential
Definition: Work done per unit charge in bringing a test charge from infinity to that point.
Formula:
V = W / q₀
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๐ Potential due to a Point Charge
Formula:
V = (1 / 4ฯฮต₀) × (q / r)
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๐ Potential due to System of Charges
Total Potential:
V_total = V₁ + V₂ + V₃ + ...
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๐งช Electrostatic Potential Energy
Energy stored due to interaction of charges:
U = (1 / 4ฯฮต₀) × (q₁q₂ / r)
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๐ Equipotential Surface
Surface where potential is constant.
Electric field is perpendicular to it.
No work is done in moving a charge on this surface.
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๐งฎ Relation Between E and V
Formula:
E = - dV / dr
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๐ Capacitors
Device used to store charge and energy.
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๐ Capacitance (C)
Defined as:
C = Q / V
Unit: Farad (F)
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๐ Parallel Plate Capacitor
Without dielectric:
C = ฮต₀A / d
With dielectric:
C = Kฮต₀A / d
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๐ Combination of Capacitors
Type Formula
Series 1/C = 1/C₁ + 1/C₂ + ...
Parallel C = C₁ + C₂ + C₃ + ...
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๐ก Energy Stored in a Capacitor
Formula:
U = ½ C V²
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๐ง Important Terms
Dielectric – Insulating material between plates
Polarization – Alignment of dipoles in dielectric
Electric Flux – Field lines through a surface
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๐ Quick Revision Table
Concept Formula
Potential (Point charge) V = (1 / 4ฯฮต₀)(q / r)
Potential Energy (2 charges) U = (1 / 4ฯฮต₀)(q₁q₂ / r)
Capacitance C = Q / V
Parallel Plate Capacitor C = ฮต₀A / d
With Dielectric C = Kฮต₀A / d
Energy Stored U = ½ C V²
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✅ Summary
Electric potential is scalar.
Equipotential surfaces show constant potential.
Capacitance depends on area, distance, and dielectric.
Capacitors store energy.
In series: capacitance decreases.
In parallel: capacitance increases.
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✍️ Written by Shahid – Founder of Shahid Notes
๐ Visit: https://shahidnotes12.blogspot.com
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