where E is the electric field vector with units of volts per meter (analogous to V of Ohm's law which has units of volts), J is the current density vector with units of amperes per unit area (analogous to I of Ohm's law which has units of amperes), and ρ " rho " is the resistivity with units of ohm·meters (analogous to R of Ohm's law which has units of ohms). The above equation is also written as J = σ E where σ " sigma " is the conductivity which is the reciprocal of ρ.