Resonance

• The natural frequency of a system is the frequency at which it oscillates without any force applied.
• If a system is acted upon by a sinusoidally varying oscillating force, it will be forced to vibrate at the forcing frequency.
• If the forcing frequency is equal to the natural frequency of the system, the amplitude of vibration would increase.
• One example is pushing a child on a swing.
• When the frequency of the push is the same as the natural frequency of the swing, the amplitude increases.
• Other useful examples of resonance include microwave ovens and circuit tuning.
• In an AC circuit, the resistance of the circuit as a whole depends on the frequency of the supply voltage and there is a certain maximum current at a specific frequency.
• When radio waves are detected by an antenna, only the radio signals very close to the 'natural frequency' of the circuit cause resonance.
• This caused the amplitude of the oscillation to increase and caused the bridge to collapse.