Lenz's Law Physics Example 4
Follow the full solution, then compare it with the other examples linked below.
Example 4
hardA superconducting ring (zero resistance) is in a magnetic field of . The external field is suddenly turned off. What happens to the flux through the ring, and why?
Solution
- 1 In a superconductor, resistance is zero, so any induced EMF produces a current that exactly maintains the original flux.
- 2 When the external field is removed, the induced current creates a magnetic field that perfectly replaces the lost external flux.
- 3 The flux through the superconducting ring remains exactly ā it is 'frozen' at its original value. The current persists indefinitely because there is no resistance.
Answer
In a superconductor, Lenz's law is perfectly realized: the induced current completely prevents any change in flux. This is the basis of persistent currents in superconducting magnets and flux trapping.
About Lenz's Law
The direction of an induced current is always such that it opposes the change in magnetic flux that produced it.
Learn more about Lenz's Law āMore Lenz's Law Examples
Example 1 easy
A north pole of a magnet is pushed toward a coil. According to Lenz's law, what pole does the coil's
Example 2 mediumA circular loop is in a magnetic field pointing into the page. The field strength decreases. Accordi
Example 3 mediumA conducting ring is dropped through a region of magnetic field. As it enters the field, the induced