By replacing Z in the above circuit with a capacitor ( C ) or inductor ( L ), negative capacitances and inductances can also be synthesized. A negative capacitance will have an I–V relation and an impedance Z C ( j ω ω ) of i = − − C d v d t Z C = − − 1 / j ω ω C where C > 0 . Applying a positive current to a negative capacitance will cause it to discharge ; its voltage will decrease. Similarly, a negative inductance will have an I–V characteristic and impedance Z L ( j ω ω ) of v = − − L d i d t Z L = − − j ω ω L A circuit having negative capacitance or inductance can be used to cancel unwanted positive capacitance or inductance in another circuit. NIC circuits were used to cancel reactance on telephone cables.