The amplitude of an oscillating body becomes maximum when the frequency of the driving force is equal to its natural resonant frequency. A driven pendulum is a very simple example of such a system.
Demonstrate the resonance of a driven pendulum. The pendulum is made by two button shaped magnets suspended on a piece of paper. A coil powered from SQ1 provides the driving force.
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.
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, 5Hz, almost tallying with its calculated natural frequency. The resonant frequency of the pendulum is given by f = 1 ⁄ (2π√(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.