2σε0\dfrac{2\sigma }{\varepsilon _0}ε02σ
σε0\dfrac{\sigma }{\varepsilon _0}ε0σ
σ2ε0\dfrac{\sigma }{2\varepsilon _0}2ε0σ
54σε05\dfrac{4\sigma }{\varepsilon _0}5ε04σ