Similar equations follow for a surface charge with surface charge density σ σ ( r ′ ) on surface S E ( r ) = 1 4 π π ε ε 0 ∬ ∬ S σ σ ( r ′ ) r ′ | r ′ | 3 d a , and for line charges with linear charge density λ λ ( r ′ ) on line L E ( r ) = 1 4 π π ε ε 0 ∫ ∫ L λ λ ( r ′ ) r ′ | r ′ | 3 d ℓ ℓ .