The voltage between two points is defined as: Δ Δ V = − − ∫ ∫ E ⋅ ⋅ d ℓ ℓ with d ℓ ℓ the element of path along the integration of electric field vector E. If the applied E field is uniform and oriented along the length of the conductor as shown in the figure, then defining the voltage V in the usual convention of being opposite in direction to the field (see figure), and with the understanding that the voltage V is measured differentially across the length of the conductor allowing us to drop the Δ symbol, the above vector equation reduces to the scalar equation: