Lenzs Law A conductor opposes any change in externally applied magnetic fields. N S N S N S = Induced current
Meissner Effect 1933 – Walther Meissner and Robert Ochsenfeld T
Superconductor: YBa2Cu3O7 Tc ~ 90 K (5.90 mV) Voltmeter: measure voltage across superconductor V = I R Demo 0 0
Superconducting State Superconducting state: T
Perfect diamagnetism Strength of diamagnetism increases linearly as the applied field increases When the applied field = Hc Field uniformly crosses sample QUENCH!! Type I Superconductors
Examples of Type I Mostly elements Highest Tc ~ 22 K (Phosphorus) Highest Hc ~ 800 G (lead) ElementTc (K) Mercury4.153 Lead7.193 Aluminum1.196 Tin3.722 Zinc0.85 Titanium0.39 Phosphoru s 14~22 (pressure)
The But... Tc too low (highest: 22K) Hc too low (highest: 800 G) Little potential for applications Discouraged!!!