# Perfect conductor and magnetic field

Inspired by this question. Can current be induced in a superconductor?

Magnetic flux of a magnet cannot enter a perfect conductor. Again moving electrons ,protons produce magnetic field(and thus magnetic flux). So what about the magnetic flux of the charged particles inside the perfect conductor(those protons and electrons which make the perfect conductor)? can magnetic field exist inside the conductor and just cannot enter from outside? If the question is not clear please inform me.

• Which moving electrons and protons ? – TZDZ Jan 15 '15 at 10:51
• Those that make the perfect conductor. – Paul Jan 15 '15 at 10:55
• Just want to point out that a perfect conductor is not a superconductor. Superconductivity is a state of matter while perfect conductivity is a property that superconductors show together with the Meissner-Ochsenfeld (field expulsion). – Ignacio Vergara Kausel Jan 15 '15 at 13:16
• @Ignacio Vergara Kause Thanks for pointing out. now is the question still making sense? – Paul Jan 15 '15 at 13:20
• To be clear, your point is : in a superconductor where current is flowing, you isolate a single electron and want to calculate the magnetic field induced by this charge inside the material ? – TZDZ Jan 16 '15 at 7:43

Edit: I realized I misunderstood the question - I'm used to dealing with superconducting coils, so my answer referred to the flux through the middle of a coil of superconductor.

No - whatever flux existed through the middle of a coil of superconductor when it became a superconductor (usually, when it was cooled below its $T_c$) is locked into the coil. Any additional magnetic flux changes around the superconductor are expelled by inducted EMFs.

In superconducting magnets, usually the superconducting coils are charged by induction while they are above $T_c$ (and therefore not yet superconducting), then they are cooled down; as long as they stay cool and in the superconducting state, the flux through the coil will not change, and the coil acts like a permanent magnet.

Also, it sounds like you think protons are moving around in superconductors, which is not the case - just the electrons.

• Actually i said protons because atoms are not stationary and atoms consist of protons. nice ans by the way. – Paul Jan 15 '15 at 15:22
• ""No - whatever flux existed in a superconductor when it became a superconductor (usually, when it was cooled below its Tc) is locked into the superconductor."" This is plainly wrong. Read about Meißner-Ochsenfeld-Effekt – Georg Jan 15 '15 at 19:45
• You're right, I didn't make it clear - I'm referring to the flux through the middle of a superconducting coil, rather than through the material of the superconductor. I'll edit my answer to make it clear what I mean. – Brionius Jan 15 '15 at 19:58
• And I also think I misunderstood the question - I guess the OP was actually asking about magnetic fields penetrating the superconducting material itself. – Brionius Jan 15 '15 at 20:16
• Your answer is very interesting even if it doesn't answer the question ! – TZDZ Jan 16 '15 at 7:37