Large and heavy coils of enamel-clad copper wire, which allow for tight, dense windings, are useful for demonstrating induced currents caused by a changing magnetic field. Students can spin magnets on a rubber band to produce enough electrical energy to light an LED. Not much, sure, but it’s still borderline magical.
Note that these hold up for a long time. Acquired in April of 1966 – just shy of six decades ago – and it’s still in regular use.
That $115.00 price marked on there? $1,171.89 in today’s dollars. Do you think we’ve recouped our investment?