Hysteresis is a phenomenon where the state of a system depends on its past history. The system’s response to a change in input depends on the system’s previous state.
A Classic Example: A Magnet
Imagine a magnet. If you apply a magnetic field, the magnet will become magnetized. When you remove the magnetic field, the magnet retains some magnetization.
This is hysteresis. The magnet’s current state (magnetized) depends on its past experience (exposure to a magnetic field).
Key Characteristics:
- Lagging Response: The output of the system lags behind the input.
- Energy Loss: Hysteresis often involves energy loss, such as the heat generated in a magnetic material due to hysteresis.
- Hysteresis Loop: A graph of the relationship between input and output often forms a loop, representing the system’s history-dependent behavior.
Other Examples of Hysteresis:
- Thermostats: Your home thermostat doesn’t immediately turn the heater on when the temperature drops below the set point. There’s a delay or “hysteresis” built in to prevent rapid on/off cycles.
- Rubber bands: A rubber band stretched to a certain length doesn’t return to its original shape immediately when released. There’s a slight delay due to hysteresis.
- Economics: Economic systems can exhibit hysteresis, where a recession can have long-lasting effects on unemployment rates even after the economy recovers.
Hysteresis is a concept that explains why many systems don’t behave in a perfectly predictable manner. It’s a reminder that the past can have a significant impact on the present.