$18.1 Conductors in electric field 5E4= “::0+E+:0=E△S= E $18.1 Conductors in electric field 4. Point discharge--lightning rod For differently shaped conductors, or for all shapes of conductors in the presence of other conductors or point charges the surface charge density varies with position on the conductor 44444++4444 亠E /ryttt tttt ttt E∝o3 0 0 S S S 0 S d d d d d 1 d letera left right ε σ ε σ ε = ∆ ⋅ = ⋅ + ⋅ + ⋅ = ∆ = ⋅ = ∫ ∫ ∫ ∫ ∫ ∫ ∆ ∆ E S E S E S E S E S E S E S Q S Q r r r r r r r r r r S r ∆ S r ∆ §18.1 Conductors in electric field 4.Point discharge—lightning rod E r E r E r E ∝ σ For differently shaped conductors , or for all shapes of conductors in the presence of other conductors or point charges the surface charge density varies with position on the conductor. §18.1 Conductors in electric field