Student experiments on parametric resonance

Some experiments on parametric effects, to be constructed by the students themselves, are described together with the discussion and questions given. Parametric oscillations were produced on a string, in a resonance circuit and a spring pendulum. The importance of phase relations for excitation of the oscillations and of nonlinearities in their stabilization was emphasized. The experiments were so organized that the students would meet unknown phenomena and problems; actually we discovered an unexpected recurrence effect in the spring pendulum.