# Resonance of a driven pendulum

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.

# Objective

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.

# 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
- Adjust 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, 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.