UNTRANSLATED .. 6.3

Resonance of a driven pendulum

Objective

Demonstrate the resonance of a driven pendulum.

_images/driven-pendulum.svg _images/resonance-pendulum.jpg

Procedure

Make a pendulum using two button magnets and a piece of paper. Suspend it and place the 3000T coil near that, as shown in figure.

  • Connect the coil between SQ1 and ground
  • Calculate the resonant frequency from the length of the pendulum
  • Scan the frequency around the expected resonance frequency

Discussion

When SQ1 reaches the resonant frequency of the pendulum, the amplitude goes up due to resonance. A 4 cm (from the center of the magnet to the axis of oscillation) long pendulum resonated at around 2,5~Hz, almost tallying with its calculated natural frequency. The resonant frequency of the pendulum is given by f = 1/(2\pi\sqrt{g/l}), where l is the distance from the center of the magnet to the point of suspension and g is the acceleration due to gravity.

Repeat the experiment by changing the length of the pendulum.