2 Replace image with one that is known to be copyright kosher edited Sep 13 '14 at 21:19 dmckee♦ 76.4k66 gold badges140140 silver badges280280 bronze badges Are you talking about the famous derivation of the displacement current, where Ampère's law is both true and false depending on what surface you choose to integrate through, despite the same boundary, as below: http://www.physics.miami.edu/~zuo/class/fall_05/supplement/Figure29_21.jpg (Image from WikiMedia commons http://commons.wikimedia.org/wiki/File:Displacement_current_in_capacitor.svg) The solution of this was to add a term to Ampère's equation that depends on the time derivative of the electric field. And then, there is no paradox anymore. Are you talking about the famous derivation of the displacement current, where Ampère's law is both true and false depending on what surface you choose to integrate through, despite the same boundary, as below: http://www.physics.miami.edu/~zuo/class/fall_05/supplement/Figure29_21.jpg The solution of this was to add a term to Ampère's equation that depends on the time derivative of the electric field. And then, there is no paradox anymore. Are you talking about the famous derivation of the displacement current, where Ampère's law is both true and false depending on what surface you choose to integrate through, despite the same boundary, as below: (Image from WikiMedia commons http://commons.wikimedia.org/wiki/File:Displacement_current_in_capacitor.svg) The solution of this was to add a term to Ampère's equation that depends on the time derivative of the electric field. And then, there is no paradox anymore. 1 answered Sep 13 '14 at 20:57 Jerry Schirmer 32.2k22 gold badges5757 silver badges110110 bronze badges Are you talking about the famous derivation of the displacement current, where Ampère's law is both true and false depending on what surface you choose to integrate through, despite the same boundary, as below: http://www.physics.miami.edu/~zuo/class/fall_05/supplement/Figure29_21.jpg The solution of this was to add a term to Ampère's equation that depends on the time derivative of the electric field. And then, there is no paradox anymore.