Electric Charges & Fields
Class 12 · Electric Charges & Fields

E vs Conductor Shape

σ ∝ 1/R_curvature — sharp regions concentrate charge and produce strongest fields.

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Key Notes

01

On a conductor, σ ∝ 1/R_curvature — sharper regions accumulate more charge.

02

Surface field E_surface = σ/ε₀ — also largest where curvature is highest.

03

This is why corona discharge starts near sharp points.

Formulas

Surface charge density

Smaller radius → higher σ → higher E.

Important Points

Lightning rods are sharply pointed — high local field ionises air, draining charge gradually.

Corona discharge: electric breakdown that starts at sharp tips around 3 MV/m.

E vs Conductor Shape notes from sciphylab (also known as SciPhy, SciPhy Lab, SciPhy Labs, Physics Lab). Class 12 physics revision for JEE Mains, JEE Advanced, NEET UG, AP Physics 1/2/C, SAT, and CUET-UG.