What happens during this workshop?
Students learn to interpret the electrical resistance vs. temperature curve of different materials. They compare the Meissner-Ochsenfeld-Effect and the Flux-Pinning-Effect when using superconductors, and how to use these effects to build a track for a levitating superconductor train.
Before taking part in this workshop, students should already know about:
- electrical resistance in normal conductors and superconductors (qualitatively)
- magnetic fields, ferromagnets, diamagnets, electromagnetic induction and eddy currents
- Cooper pairs (optional)
- Electrical resistance: The electrical resistance is a measure of the difficulty to pass an electric current through a material. Materials with a low electrical resistance are called conductors, whereas materials with a high electrical resistance are called resistors. The electrical resistance of a conductor is lower at lower temperatures.
- Ohm’s law: Ohm's law states that the current (I) through a conductor is directly proportional to the voltage (U) applied to the conductor. The electrical resistance (R) is the constant of proportionality: U = R ⋅ I
- Induction and eddy currents: When a conductor moves into a magnetic field, or when the magnetic field surrounding a conductor changes, currents are induced in the conductor. Depending on the shape of the conductors these currents form loops – so called eddy currents. Eddy currents create a magnetic field.
Watch this video by Freesciencelessons about Understanding Resistance
Watch this video by Aaron MacRaighne, Matt Barr and Fiona Meade covering eddy currents, magnetic braking and Lenz's Law
Quiz: You can use the quiz questions below to find out if your students are well prepared for this experiment:
- How does the electrical resistance of copper change with increasing temperature?
a) The electrical resistance increases.
b) The electrical resistance decreases.
c) The electrical resistance does not change.
d) The electrical resistance changes direction.
- U = R⋅I means at a constant current and constant temperature: When the voltage increases….
a) the resistance drops.
b) the resistance increases.
c) the resistance remains unchanged.
What happens if a bar magnet approaches a conductor?
a) Eddy currents are induced in the conductor.
b) A magnetic field is induced in the conductor.
c) The electrical resistance in the conductor increases.
d) Nothing happens.
Summary and link to CERN physics:
Below a certain temperature, superconductors lose their electrical resistance. This can be used in high energy physics at CERN.
The LHC uses several thousand special superconducting electromagnets. Superconductive materials such as NbTi allow extremely high currents in these electromagnets, generating a magnetic field of several Tesla. CERN is also testing new material to build even stronger superconducting electromagnets for the next generation of particle accelerators.